P2178System Too Rich Off Idle (Bank 1)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- P2178 is the rich-side limit of the bank 1 load adaptation: above idle the long-term trim has to take away more fuel than allowed. GM's Bosch-based V6 engines of 2005 and 2008 set it below a factor of 0.78, the 2023 and 2024 tables below 0.77, each after two trips. Saab's 9-5 2.0T uses the same window as for the lean code, 6.9 to 41.7 g/s, 18 to 80 % load and 1280 to 4000 rpm, and wants 4 s without break or 50 s in total. VW's 2014 CC 2.0 TSI accepts down to -21 %. A rich error that grows with load usually means an air mass sensor reading too high, excessive fuel pressure or injectors delivering too much. Mercedes saw it on the M254 with fuel boiling in the low-pressure side; Jaguar Land Rover lists P2178 with P0191 on Ingenium petrol engines and cured it with new PCM calibration.
- What you may notice
- Check engine lamp on after two trips
- Higher fuel consumption, fuel smell
- Likely causes
- PossibleAir mass sensor reading too high
- PossibleFuel pressure too high or injectors over-delivering
- PossibleCalibration error fixed by a software update
- RareFuel vapour from purge or boiling fuel in the low-pressure system
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €0 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.