OBD-II · Engine and powertrain (P)
P0170
Fuel trim malfunction bank 1
What it means
The ECU cannot keep fuel correction within its normal range.
Symptoms
- engine warning light
- possible rough idle or hesitation
- higher fuel consumption
Likely causes, most likely first
| No. | Cause |
|---|---|
| 01 | vacuum leak |
| 02 | MAF error |
| 03 | fuel pressure issue |
| 04 | lambda sensor fault |
| 05 | exhaust leak |
What to check, step by step
- 01Read short- and long-term fuel trims to see whether bank 1 is running lean or rich
- 02If trims are strongly positive (lean), follow the P0171 checks: vacuum leaks, crankcase breather, MAF and fuel pressure
- 03If trims are strongly negative (rich), follow the P0172 checks: purge valve, injectors, fuel pressure
- 04Check the upstream lambda sensor signal and look for exhaust leaks before it
- 05On LPG-converted cars, compare trims on petrol and on gas