Applicable Systems
OBD-II
Symptoms
Fuel trim for bank 1 exceeds -25% (rich); ECM removing maximum fuel; possible leaking injector or high fuel pressure.
Possible Causes
- Fuel injector leaking/stacking open
- Fuel pressure regulator stuck high
- ECT sensor reading cold (stuck rich)
- MAF sensor over-reading
Troubleshooting Steps
- Step 1: Check STFT/LTFT (should be > -15%)
Trims within range after repair - Step 2: Check fuel pressure (should be within spec)
Pressure within spec - Step 3: Check ECT sensor reading (should match actual temp)
ECT reading accurate - Step 4: Perform injector balance test
All injectors flow equally - Step 5: Replace leaking injector or faulty regulator
Fuel trims return to normal
How to Reset
Clear with OBD-II scanner after repair; reset trims.
Common Replacement Parts
- Fuel Injector (OEM spec)
- Fuel Pressure Regulator
Frequently Asked Questions
- Q: How to test for leaking injector?
Pressurize fuel rail and monitor pressure drop. Leaking injector will cause pressure to drop faster than others. Can also inspect spark plugs for clean (washed) appearance.
Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II