P2177: System too lean off idle (bank 1)

What P2177 means

The ECU adjusts the amount of fuel so the mix with the air is just right. This code means that on bank 1, away from idle (while driving or with the engine revving), the mixture is lean, with too much air, and the correction has hit its limit. It is usually unmetered air getting in or not enough fuel arriving.

Most common causes

• An air leak between the airflow sensor and the engine (loose or split hose)
• A dirty or faulty airflow sensor reading less air than there really is
• A broken vacuum or crankcase breather hose
• A clogged fuel filter or weak fuel pump
• Dirty or partly blocked injectors
• An exhaust leak ahead of the oxygen sensor

Symptoms

• Engine warning light on
• Hesitation or lack of power when accelerating
• Slightly higher consumption or harder starting
• May fail the emissions test at inspection

Can you drive with P2177?

With care You can drive, but running lean for long can cause misfires and make the engine run hot. Have it looked at soon.

How to check it

Use a live data reader to watch bank 1 long term fuel trim at idle and at around 2,500 rpm: if it climbs much higher at the higher revs, suspect the airflow sensor or the fuel supply.

How to read and clear P2177 with Final OBD

Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P2177 with this same explanation and whether it’s confirmed, pending or permanent.

With Free you read this code with its short description for nothing, and clear it if the engine stores it over standard OBD. With Pro you get the full explanation, how the car was running when it was logged (revs, temperature, load) and clearing in every control unit.

Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before the ITV. It’s all in how to read and clear fault codes and in the ITV and OBD.

Similar codes

• P2128 Throttle or pedal position sensor E circuit high
• P2135 Throttle or pedal position sensors A and B voltage mismatch
• P2138 Throttle or pedal position sensors D and E voltage mismatch
• P2146 Fuel injector group A supply voltage circuit or open
• P2178 Mixture too rich away from idle (bank 1)
• P2179 Mixture too lean away from idle (bank 2)
• P2187 Mixture too lean at idle (bank 1)
• P2188 Mixture too rich at idle (bank 1)
• P2100 Throttle actuator A control motor circuit open
• P2101 Throttle actuator A control motor circuit range or performance
• P2102 Throttle actuator A control motor circuit low
• P2104 Throttle control system: forced idle

P2177 is a generic code, so it means the same on any make, for example on Citroën, Ford, Hyundai, Mercedes-Benz, Renault, Volvo. See what Final OBD does on your car in makes and models.