P0157

SYMPTOM
P0157-02 SENSOR 2/2 CIRCUIT LOW

WHEN MONITORED
Engine running for less than 30 seconds and the 02 Sensor Heater Temperature is less than 251 °C (484 °F) with battery voltage greater 10.99 volts.

SET CONDITION
The oxygen sensor signal voltage is below 2.5196 volts for 3 seconds after starting engine. One Trip Fault. Three good trips to turn off the MIL.

POSSIBLE CAUSES
- (K904) 02 DOWNSTREAM RETURN CIRCUIT SHORTED TO GROUND
- (K243) 02 2/2 SIGNAL CIRCUIT SHORTED TO GROUND
- (K243) 02 SIGNAL CIRCUIT SHORTED TO (K904) 02 DOWNSTREAM RETURN CIRCUIT
- (K243) 02 SIGNAL CIRCUIT SHORTED TO THE (Z992) 02 2/2 HEATER GROUND CIRCUIT
- 02 SENSOR
- PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Scan Tool Testing and Procedures

DIAGNOSTIC TEST
1. 02 SENSOR BELOW 2.52 VOLTS





Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, read the 2/2 02 Sensor voltage.
Is the voltage below 2.52 volts?
Yes>> Go To 2
No>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5. Powertrain Verification Test - Ver 5

2. (K243) 02 2/2 SIGNAL CIRCUIT





Turn the ignition off.
Disconnect the 2/2 02 Sensor harness connector.
Ignition on, engine not running.
With a scan tool, monitor the 2/2 02 Sensor voltage.
Is the 02 Sensor voltage above 4.8 volts?
Yes>> Go To 3
No>> Go To 5

3. 02 SENSOR





Measure the voltage on the (K904) 02 Downstream Return circuit in the 02 Sensor harness connector.
Is the voltage at 2.5 volts?
Yes>> Replace the 02 Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 4

4. (K904) 02 DOWNSTREAM RETURN CIRCUIT SHORTED TO GROUND





Turn the ignition off. Disconnect the PCM harness connectors.
Measure the resistance between ground and the (K904) 02 Downstream Return circuit in the 02 Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short to ground in the (K904) 02 Downstream Return circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 8

5. (K243) 02 2/2 SIGNAL CIRCUIT SHORTED TO GROUND





Turn the ignition off. Disconnect the PCM harness connectors.
Measure the resistance between ground and the (K243) 02 2/2 Signal circuit in the 02 Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short to ground in the (K243) 02 2/2 Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 6

6. (K243) 02 2/2 SIGNAL CIRCUIT SHORTED TO THE (K904) 02 DOWNSTREAM RETURN CIRCUIT





Measure the resistance between the (K243) 02 2/2 Signal circuit and the (K904) 02 Downstream Return circuit in the 02 Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short between the (K904) 02 Downstream Return circuit and the (K243) 02 2/2 Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 7

7. (K243) 02 2/2 SIGNAL CIRCUIT SHORTED TO (Z992) 02 2/2 HEATER GROUND CIRCUIT





Measure the resistance between the (K243) 02 2/2 Signal circuit and the (Z992) 02 2/2 Heater ground circuit in the 02 Sensor harness connector.
Is the resistance below 100 ohms?
Yes>> Repair the short between the (Z992) 02 2/2 Heater ground circuit and the (K243) 02 2/2 Signal circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Go To 8

8. PCM

Note: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes>> Repair as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.
No>> Replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-5.