Toggle Side Panel

Shopping Cart

No products in the basket.

Shopping Cart

No products in the basket.

Close search
Home / DTC / P2271 — O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2

P2271 — O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2

Detailed page for trouble code P2271.

34,405codes
59brands
11,914generic
22,491specific
All codes P-codes (Powertrain) B-codes (Body) C-codes (Chassis) U-codes (Network/User) Tesla Alerts
Reset
Code

P2271

Generic P — Powertrain

O2 Sensor Signal Biased/Stuck Rich Bank 1 Sensor 2

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

Causes

  • Faulty Bank 1 Sensor 2 (HO2S, downstream O2 sensor) — contamination or internal damage
  • Signal circuit shorted to battery voltage or poor/shorted connector
  • Open or poor ground on sensor circuit or PCM ground
  • Fuel system over‑fueling (high fuel pressure, leaking injector, stuck open injector)
  • Faulty upstream sensor (Bank 1 Sensor 1) or fuel trim control causing rich running
  • Faulty MAF/MAF contamination or CTS reading incorrect (engine running rich)

Symptoms

  • Check Engine Light (MIL) illuminated with P2271 stored
  • Reduced fuel economy
  • Black exhaust smoke or strong fuel smell (if running very rich)
  • Rough idle or hesitation under some conditions (if rich enough to affect drivability)
  • Failed emissions test or elevated tailpipe HC/CO

What to check

  • Retrieve freeze frame and live data — record Bank 1 Sensor 1 and Sensor 2 voltages, short‑term and long‑term fuel trims, fuel pressure, engine coolant temp, MAF voltage/counts and any misfire counters
  • Visually inspect wiring and connector for Bank 1 Sensor 2 for damage, corrosion, or pin pushed out
  • Backprobe O2 sensor signal with a DMM/scan tool and compare to Bank 1 Sensor 1
  • Check for shorts to 12V on the sensor signal circuit and for open/poor ground
  • Measure heater circuit resistance and supply voltage for the downstream sensor (if equipped)
  • Check fuel pressure and compare to spec (static and under load)

Signal parameters

  • Narrowband O2 sensor typical voltage range: ~0.1–0.9 V; upstream sensor toggles rapidly, downstream sensor is steadier
  • Downstream (post‑cat) sensor normally near ~0.4–0.6 V at steady stoichiometry with small variation — prolonged >~0.7–0.8 V indicates rich bias
  • If sensor signal is held near battery voltage (close to 12 V) it indicates a short to battery or signal reference problem
  • Heater resistance (typical range): ~3–30 Ω depending on sensor; consult vehicle spec — open heater or no heater current indicates heater fault
  • Fuel trim expectation: LTFT should be near 0% (±10%). Large negative LTFT indicates over‑fueling (rich).

Diagnostic algorithm

  1. Read and record DTCs, freeze frame, and live data (Bank1 S1 & S2 voltages, STFT/LTFT, fuel pressure, MAF, CTS).
  2. Visually inspect Bank 1 Sensor 2 connector and wiring for damage, corrosion, melted insulation, or frame/chassis contact.
  3. With key on engine off, backprobe the sensor connector: verify reference, ground and heater supply voltages per vehicle spec.
  4. Start engine and monitor sensor voltages: compare Bank1 Sensor1 (upstream) vs Bank1 Sensor2 (downstream). Upstream should switch; downstream should be steady. If both are high, suspect rich condition; if only S2 high, suspect S2/wiring/PCM.
  5. Check for short to 12V on the S2 signal circuit (disconnect sensor and measure voltage at harness). If harness reads 12V with sensor disconnected, trace wiring for short or damaged insulation.
  6. Measure heater resistance and verify heater circuit operation (power/ground present when commanded). Replace sensor if heater open or not functioning.
  7. Check fuel system: measure fuel pressure and inspect for leaking injectors (fuel smell, wetness, injector balance test) and check for stuck purge valve.
  8. Inspect MAF and CTS inputs for erroneous readings that could cause a rich condition; clean/replace MAF if contaminated and verify engine coolant temp sensor operation.
  9. If sensor and wiring test normal but rich condition persists, investigate fuel control (injectors, pressure regulator, ECU control) and catalytic converter condition (backpressure test, visual inspection, catalyst efficiency codes).
  10. If wiring and fuel system verify OK, replace Bank 1 Sensor 2, clear codes and perform a full drive cycle to confirm code does not return.
  11. Safety note: exhaust and sensors are hot — allow cooling or use appropriate protection when working near exhaust components. Disconnect battery when replacing sensors on vehicles that require it.

Likely causes

  • Contaminated or failed Bank 1 Sensor 2
  • Short to 12V on the sensor signal circuit or poor connector
  • Fuel pressure regulator or fuel pump causing high fuel pressure
  • Leaking/faulty injector(s) on bank 1
  • Bad upstream O2 sensor or MAF/CTS causing closed-loop fuel control to run rich

Fault status

⚠️ Status
PCM detected Bank 1 Sensor 2 signal biased/stuck rich: downstream oxygen sensor voltage remains higher than expected or does not follow expected pattern. Possible causes include a bad downstream sensor, short to 12V, over‑fueling (high fuel pressure or leaking injector), upstream fuel trim control issues, or catalyst contamination. Further diagnosis required to isolate sensor, wiring, fuel system, or PCM fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours

Similar codes

P2191 P0138 P0135 P0172 P0420 P2270
8,460

The library contains 8,460 repair and diagnostic manuals. Choose a brand to open the full manual tree by year, model and trim.

ALFA ROMEO
89
AUDI
1,160
BMW
479
CHEVROLET
456
DAEWOO
75
FIAT
26
GENESIS
207
HUMMER
138
HYUNDAI
371
ISUZU
86
LAND ROVER
320
LEXUS
280
LINCOLN
166
MERCEDES-BENZ
856
MERCURY
296
MITSUBISHI
406
PORSCHE
136
TESLA
58
TOYOTA
2,042
TRIUMPH
131
VOLKSWAGEN
461
VOLVO
221
Your experience will help others
+100 karma for a short comment :)
Keep it short and practical. Up to 500 characters.
Send to email
Code

P2271

LAND ROVER P — Powertrain

The oxygen sensor signal became rich. Bank 1 - sensor 2

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

Causes

  • Faulty Bank 1 Sensor 2 (HO2S, downstream O2 sensor) — contamination or internal damage
  • Signal circuit shorted to battery voltage or poor/shorted connector
  • Open or poor ground on sensor circuit or PCM ground
  • Fuel system over‑fueling (high fuel pressure, leaking injector, stuck open injector)
  • Faulty upstream sensor (Bank 1 Sensor 1) or fuel trim control causing rich running
  • Faulty MAF/MAF contamination or CTS reading incorrect (engine running rich)

Symptoms

  • Check Engine Light (MIL) illuminated with P2271 stored
  • Reduced fuel economy
  • Black exhaust smoke or strong fuel smell (if running very rich)
  • Rough idle or hesitation under some conditions (if rich enough to affect drivability)
  • Failed emissions test or elevated tailpipe HC/CO

What to check

  • Retrieve freeze frame and live data — record Bank 1 Sensor 1 and Sensor 2 voltages, short‑term and long‑term fuel trims, fuel pressure, engine coolant temp, MAF voltage/counts and any misfire counters
  • Visually inspect wiring and connector for Bank 1 Sensor 2 for damage, corrosion, or pin pushed out
  • Backprobe O2 sensor signal with a DMM/scan tool and compare to Bank 1 Sensor 1
  • Check for shorts to 12V on the sensor signal circuit and for open/poor ground
  • Measure heater circuit resistance and supply voltage for the downstream sensor (if equipped)
  • Check fuel pressure and compare to spec (static and under load)

Signal parameters

  • Narrowband O2 sensor typical voltage range: ~0.1–0.9 V; upstream sensor toggles rapidly, downstream sensor is steadier
  • Downstream (post‑cat) sensor normally near ~0.4–0.6 V at steady stoichiometry with small variation — prolonged >~0.7–0.8 V indicates rich bias
  • If sensor signal is held near battery voltage (close to 12 V) it indicates a short to battery or signal reference problem
  • Heater resistance (typical range): ~3–30 Ω depending on sensor; consult vehicle spec — open heater or no heater current indicates heater fault
  • Fuel trim expectation: LTFT should be near 0% (±10%). Large negative LTFT indicates over‑fueling (rich).

Diagnostic algorithm

  1. Read and record DTCs, freeze frame, and live data (Bank1 S1 & S2 voltages, STFT/LTFT, fuel pressure, MAF, CTS).
  2. Visually inspect Bank 1 Sensor 2 connector and wiring for damage, corrosion, melted insulation, or frame/chassis contact.
  3. With key on engine off, backprobe the sensor connector: verify reference, ground and heater supply voltages per vehicle spec.
  4. Start engine and monitor sensor voltages: compare Bank1 Sensor1 (upstream) vs Bank1 Sensor2 (downstream). Upstream should switch; downstream should be steady. If both are high, suspect rich condition; if only S2 high, suspect S2/wiring/PCM.
  5. Check for short to 12V on the S2 signal circuit (disconnect sensor and measure voltage at harness). If harness reads 12V with sensor disconnected, trace wiring for short or damaged insulation.
  6. Measure heater resistance and verify heater circuit operation (power/ground present when commanded). Replace sensor if heater open or not functioning.
  7. Check fuel system: measure fuel pressure and inspect for leaking injectors (fuel smell, wetness, injector balance test) and check for stuck purge valve.
  8. Inspect MAF and CTS inputs for erroneous readings that could cause a rich condition; clean/replace MAF if contaminated and verify engine coolant temp sensor operation.
  9. If sensor and wiring test normal but rich condition persists, investigate fuel control (injectors, pressure regulator, ECU control) and catalytic converter condition (backpressure test, visual inspection, catalyst efficiency codes).
  10. If wiring and fuel system verify OK, replace Bank 1 Sensor 2, clear codes and perform a full drive cycle to confirm code does not return.
  11. Safety note: exhaust and sensors are hot — allow cooling or use appropriate protection when working near exhaust components. Disconnect battery when replacing sensors on vehicles that require it.

Likely causes

  • Contaminated or failed Bank 1 Sensor 2
  • Short to 12V on the sensor signal circuit or poor connector
  • Fuel pressure regulator or fuel pump causing high fuel pressure
  • Leaking/faulty injector(s) on bank 1
  • Bad upstream O2 sensor or MAF/CTS causing closed-loop fuel control to run rich

Fault status

⚠️ Status
PCM detected Bank 1 Sensor 2 signal biased/stuck rich: downstream oxygen sensor voltage remains higher than expected or does not follow expected pattern. Possible causes include a bad downstream sensor, short to 12V, over‑fueling (high fuel pressure or leaking injector), upstream fuel trim control issues, or catalyst contamination. Further diagnosis required to isolate sensor, wiring, fuel system, or PCM fault.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1-3 hours

Similar codes

P2191 P0138 P0135 P0172 P0420 P2270
320

Browse 320 LAND ROVER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

LAND ROVER

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 .