Powertrain, generic (extended)

P2178 System Too Rich Off Idle (Bank 1)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

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.

Likely causes

Air mass sensor reading too high
Fuel pressure too high or injectors over-delivering
Calibration error fixed by a software update
Fuel vapour from purge or boiling fuel in the low-pressure system

Symptoms

  • Check engine lamp on after two trips
  • Higher fuel consumption, fuel smell

Repair estimate

DifficultyMediumDIY possible
Parts and labour€0–700
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

mass air flow sensorfuel pressure regulatorfuel injectorevap purge valve

Related codes

P2177P2180P2188P0172P0101

References: saabwisonline.com, gsi.ext.gm.com, gsi.ext.gm.com, static.nhtsa.gov.