Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / P0172 — Fuel trim -Åtoo rich

P0172 — Fuel trim -Åtoo rich

Detailed page for trouble code P0172.

35,619codes
59brands
11,925generic
23,694specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

P0172

MITSUBISHI P — Powertrain

Fuel trim -Åtoo rich

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

Causes

  • Faulty or slow oxygen (O2/HO2S) sensor(s) on bank 1
  • Contaminated or faulty mass air flow (MAF) sensor
  • High fuel pressure (stuck/regulator failure or blocked fuel return)
  • Leaking or stuck-open fuel injector(s) on bank 1
  • Excessive fuel vapor purge (stuck open EVAP purge valve)
  • Intake air restriction (clogged air filter or collapsed intake duct)

Symptoms

  • Poor fuel economy (noticeably higher fuel consumption)
  • Black exhaust smoke or strong fuel smell from tailpipe
  • Rough idle, hesitation or reduced engine performance
  • Failed emissions test (high HC/CO/CO2)
  • Illuminated check engine light (CEL) with P0172 set

What to check

  • Retrieve freeze frame and full scan for related/side codes (O2, MAF, fuel system)
  • Monitor Live Data: short-term (STFT) and long-term fuel trim (LTFT) for bank 1, oxygen sensor voltage/waveform, and MAF readings
  • Measure fuel rail pressure at idle and under load; compare to spec
  • Inspect air intake path: air filter, snorkel, intake for restrictions or collapsed tubing
  • Inspect injectors on bank 1 for leaks or stuck-open condition (visual/drip test or fuel pressure decay)
  • Check EVAP purge valve operation (stuck open will add fuel vapors)

Signal parameters

  • LTFT (Bank 1): significantly negative or large negative numbers indicate rich condition (typical +/-10% range)
  • STFT (Bank 1): negative values when system trimming rich
  • O2 (Bank 1 HO2S narrowband): low voltage (~0.1–0.3 V) or no switching indicates rich/failed sensor
  • MAF: g/s or voltage lower-than-expected for given RPM/load can cause overfueling
  • Fuel rail pressure: compare measured psi/bar to manufacturer spec (should not be above spec)
  • Intake air temperature (IAT) and coolant temp: unusually low coolant temp may command extra fuel

Diagnostic algorithm

  1. Read and record codes and freeze-frame; check for related codes (O2 heater faults, MAF codes, fuel pressure codes).
  2. With engine warm and at idle, record STFT/LTFT for bank 1 and O2 sensor waveform. Look for constant low O2 voltage or stuck rich fuel trims.
  3. Inspect air intake & filter for restrictions; clean/replace if clogged. Visually check intake tubing for collapse or blockage.
  4. Clean MAF sensor with approved cleaner and re-test; swap with known-good unit if available to confirm.
  5. Measure fuel rail/static pressure and pressure under running conditions; compare to spec. If high, isolate fuel pressure regulator and return line.
  6. Perform injector inspection: conduct a balance/flow test or remove rail and check for dripping injectors with engine off and pressurized rail.
  7. Test EVAP purge valve operation for proper open/close; replace if stuck open.
  8. Verify coolant temperature sensor reading against ambient and block temp; replace if it falsely indicates cold.
  9. If sensors/wiring suspect, inspect and back-probe connectors, and check reference voltages/grounds. Repair any faults.
  10. After corrective action, clear codes and perform a test drive/road cycle while monitoring fuel trims and O2 response to confirm the condition is resolved.

Likely causes

  • O2 sensor on bank 1 reporting low voltage (always rich) or not switching
  • High fuel rail pressure caused by a bad regulator or blocked return
  • MAF sensor contamination causing under-reported air flow
  • Leaking injector(s) saturating cylinder(s) with excess fuel
  • Stuck-open EVAP purge valve introducing excess fuel vapor

Fault status

⚠️ Status
P0172 — System Too Rich (Bank 1). ECU measured mixture richer than expected on bank 1; investigate sensors, fuel pressure, injectors, and intake.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3 hours (varies by vehicle and parts access)

Similar codes

P0171 P0175 P0100 P0135 P2195
406

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

MITSUBISHI

Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email

Report

Harassment or bullying behavior
Contains mature or sensitive content
Contains misleading or false information
Contains abusive or derogatory content
Contains spam, fake content or potential malware

Block Member?

Please confirm you want to block this member.

You will no longer be able to:

  • See blocked member's posts
  • Mention this member in posts
  • Invite this member to groups
  • Message this member
  • Add this member as a connection

Please note: This action will also remove this member from your connections and send a report to the site admin. Please allow a few minutes for this process to complete.

Report

You have already reported this .