Troubleshooting by Diagnostic Trouble Code - DTC P1123/P1124/P1127/P1128

DESCRIPTION AND OPERATION

In addition to various sensors, the air-fuel ratio control system includes the following components and systems:

• Intake system.

• Exhaust system.

• Evaporative emission control system (including the EVAP canister purge solenoid valve).

• Fuel injectors.

• Fuel pressure regulator.

• Fuel pump.

In order for the air-fuel ratio to remain within the allowable range, all sensors, components, and systems that affect the air-fuel ratio must function normally.

DTC ENABLE CONDITIONS [FOR SHORT-TERM FUEL TRIM]

The ECM will store the DTC and illuminate the MIL if, during two driving cycles within 30 seconds, either the short-term fuel trim value is positive, within 10-15% (i.e., large correction to increase injector pulse width) [for P1123], or the short-term fuel trim additional value is less than 0.4 msec, or the short-term fuel trim value is negative, within 10-15% (i.e., large correction to decrease injector pulse width) [for P1124], under the following conditions:

1. The ECM performs closed-loop air-fuel ratio control.

2. Engine speed is less than 1000 rpm.

3. Engine coolant temperature is above 70°C.

4. Evaporative emission (EVAP) canister purge is not being performed.

5. Intake air flow is less than 7.5 g/s [for P1123] or 5.5 g/s [for P1124].

[FOR LONG-TERM FUEL TRIM]

The ECM will store the DTC and illuminate the MIL if, during two driving cycles within 30 seconds, either the long-term fuel trim multiplicative value is less than 77% (i.e., maximum allowable correction to compensate for constant positive deviation of short-term fuel trim) [for P1127], or the long-term fuel trim value is negative, within 10-15% (i.e., maximum allowable correction to compensate for constant negative deviation of short-term fuel trim) [for P1128], under the following conditions:

1. Engine load (fuel injection pulse width) exceeds 1.8 msec.

2. [For P1127] The ECM is performing air-fuel ratio feedback control (closed-loop).

3. Engine coolant temperature is above 70°C.

4. Evaporative emission (EVAP) canister purge is not being performed.

5. Intake air flow is less than 5.5 g/s.

6. [For P1128] Engine speed is less than 1000 rpm.

INSPECTION PROCEDURE

INSPECTION PROCEDURE