P1128

Test 1-4:

Test 5-8:

Test 9-11:

Test 12-14:

SYMPTOM
P1128-CLOSED LOOP FUELING NOT ACHIEVED - BANK 1

TEST NOTE
This symptom is diagnosed using the test P0171-FUEL SYSTEM 1/1 LEAN.

WHEN MONITORED
After engine running.

SET CONDITION
The enable conditions are met and the upstream bank 1 O2 sensors have not been in closed loop control at least once on each of two consecutive trips, the MIL illuminates and a DTC is set. Two Trip Fault. Three good trips to turn off the MIL.

POSSIBLE CAUSES
- Good trip equal to zero
- Restricted fuel supply line
- Fuel pump inlet strainer plugged
- Fuel pump module
- O2 sensor
- O2 signal circuit
- O2 return circuit
- O2 sensor heater operation
- Throttle position sensor sweep
- MAP sensor operation
- ECT sensor operation
- Engine mechanical problem
- Fuel contamination/exhaust leak