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Home / DTC / P0172 — System Too Rich Bank 1

P0172 — System Too Rich Bank 1

Detailed page for trouble code P0172.

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23,694specific
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P0172

Generic P — Powertrain

System Too Rich Bank 1

Brand: Generic
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

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P0171 P0174 P0175 P2195 P2197
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Code

P0172

GWM P — Powertrain

- A mixture of rich (bank 1)

Brand: GWM
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
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Code

P0172

HUMMER P — Powertrain

Fuel Trim System Rich Bank 1

Brand: HUMMER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
Repair manuals

Manual library for HUMMER

138

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Code

P0172

HYUNDAI P — Powertrain

Fuel Trim System Too Rich (Bank 1)

Brand: HYUNDAI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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Code

P0172

LAND ROVER P — Powertrain

System too rich (bank 1)

Brand: LAND ROVER
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
413

Browse 413 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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Code

P0172

MITSUBISHI P — Powertrain

Fuel trim -Åtoo rich

Brand: MITSUBISHI
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

MITSUBISHI

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+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P0172

VOLKSWAGEN P — Powertrain

System Too Rich (Bank 1)

Brand: VOLKSWAGEN
Type: P — Powertrain
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Leaking or stuck-open fuel injector(s) on bank 1
  • High fuel pressure (faulty fuel pressure regulator or return restriction)
  • Contaminated or faulty mass airflow (MAF) sensor
  • Faulty intake air temperature (IAT) or engine coolant temperature (ECT) sensor reporting cold
  • Faulty upstream oxygen sensor (HO2S) or sensor wiring shorted to voltage
  • Incorrect fuel trim due to ECU or software faults (rare)

Symptoms

  • Check Engine Light illuminated
  • Poor fuel economy
  • Black smoke from exhaust or strong fuel smell
  • Rough idle or hesitation on acceleration
  • Fouled or blackened spark plugs on bank 1
  • Possible drivability problems (misfire, stumble)

What to check

  • Read stored freeze-frame and live data (LTFT/STFT for bank 1, O2 voltages, MAF grams/sec or volts, fuel trims)
  • Inspect for obvious fuel leaks and sniff for fuel smell around injectors and rail
  • Visually inspect air intake, air filter, and MAF sensor for contamination or damage
  • Measure fuel rail pressure with a gauge at key-on/run and during idle and load
  • Check upstream O2 sensor behavior (voltage should switch; a constant high voltage ~0.8–1.0 V may indicate rich or a bad sensor)
  • Inspect wiring and connectors for injectors, MAF, O2, ECT/IAT and fuel pressure regulator

Signal parameters

  • Long Term Fuel Trim (LTFT) Bank 1: significantly negative (example:
  • Short Term Fuel Trim (STFT) Bank 1: sustained negative values (example: -10% or lower under steady conditions)
  • Upstream O2 (HO2S) Bank 1 voltage: steady high (~0.7–1.0 V) or non-switching when it should oscillate
  • MAF sensor: unexpected low airflow reading for given RPM/load (g/s or V out of expected range) or intermittent signal
  • Fuel rail pressure: above factory spec (varies by system; consult vehicle spec — e.g., > nominal by ~10% can cause richness)
  • Engine coolant temp or IAT: sensor reporting higher than actual cold reading (ECU sees colder than actual => enrichment)

Diagnostic algorithm

  1. Retrieve freeze-frame data and live PID values: note LTFT/STFT bank 1, MAF, fuel pressure, O2 voltages, ECT/IAT.
  2. Visually inspect intake and MAF; clean MAF with recommended cleaner if contaminated, then retest.
  3. Check for vacuum leaks (while leaks usually cause lean codes, verify none are causing incorrect sensor readings).
  4. Test fuel pressure at the rail at idle and during snap throttle; compare to spec. If high, inspect fuel pressure regulator and return line.
  5. Perform an injector leak test or fuel injector balance test on bank 1; look for leaking or over-delivering injector(s).
  6. Monitor upstream O2 sensor: command a rich/lean response (if vehicle supports) or watch voltage with throttle changes. Replace if sensor is stuck high and other causes ruled out.
  7. Inspect and test IAT and ECT sensors for correct resistance/voltage vs temperature. Replace if reading incorrectly cold.
  8. Disconnect MAF (or substitute with known-good) and observe fuel trims: if trims normalize when MAF disconnected, suspect MAF sensor or intake metering issue.
  9. Check injector wiring and driver outputs with a scope or meter for proper pulse and no leakage to ground.
  10. Clear codes and test drive to verify repair. If code returns, follow targeted tests based on final suspicious component(s).

Likely causes

  • Stuck-open or leaking injector(s) on bank 1 (most common)
  • Excessive fuel rail pressure from a bad regulator or clogged return
  • MAF under-reporting airflow because of contamination or failure
  • Faulty coolant or intake air temp sensor commanding enrichment
  • Upstream O2 sensor stuck high (falsely indicating rich)
  • Fuel system return line restriction or collapsed hose

Fault status

⚠️ Status
ECM detects bank 1 running richer than calibrated threshold (excess fuel / insufficient air) — corrective action required to prevent catalyst damage and poor fuel economy.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

P0171 P0174 P0175 P2195 P2197
626

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