P0157-O2 SENSOR 2/2 CIRCUIT LOW
For a complete wiring diagram Refer to Section 8W.
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When Monitored:
Engine running for less than 30 seconds and the O2 Sensor Heater Temperature is less than 251 degrees C (484 degrees F) with battery voltage greater 10.99 volts.
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Set Condition:
The oxygen sensor signal voltage is below 2.5196 volts for 3 seconds after starting engine. Two Trip Fault. Three good trips to turn off the MIL.
Possible Causes
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(K904) O2 RETURN DOWNSTREAM CIRCUIT SHORTED TO GROUND
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(K243) O2 2/2 SIGNAL CIRCUIT SHORTED TO GROUND
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(K243) O2 SIGNAL CIRCUIT SHORTED TO THE (K904) O2 RETURN DOWNSTREAM CIRCUIT
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(K243) O2 SIGNAL CIRCUIT SHORTED TO THE (Z906) O2 2/2 HEATER GROUND CIRCUIT
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O2 SENSOR
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PCM
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Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
(Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).
Diagnostic Test
1.
O2 SENSOR BELOW 2.52 VOLTS
Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, read the 2/2 O2 Sensor voltage.
Is the voltage below 2.52 volts?
Yes
No
2.
(K243) O2 2/2 SIGNAL CIRCUIT
Turn the ignition off.
Disconnect the 2/2 O2 Sensor harness connector.
Ignition on, engine not running.
With a scan tool, monitor the 2/2 O2 Sensor voltage.
Is the O2 Sensor voltage above 4.8 volts?
Yes
No
3.
O2 SENSOR
Measure the voltage on the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Is the voltage at 2.5 volts?
Yes
No
4.
(K904) O2 RETURN DOWNSTREAM CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C1 PCM harness connector.
Measure the resistance between ground and the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Is the resistance below 100 ohms?
Yes
No
5.
(K243) O2 2/2 SIGNAL CIRCUIT SHORTED TO GROUND
Turn the ignition off.
Disconnect the C1 PCM harness connector.
Measure the resistance between ground and the (K243) O2 2/2 Signal circuit in the O2 Sensor harness connector.
Is the resistance below 100 ohms?
Yes
No
6.
(K243) O2 2/2 SIGNAL CIRCUIT SHORTED TO THE (K904) O2 RETURN DOWNSTREAM CIRCUIT
Measure the resistance between the (K243) O2 2/2 Signal circuit and the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Is the resistance below 100 ohms?
Yes
No
7.
(K243) O2 2/2 SIGNAL CIRCUIT SHORTED TO THE (Z906) O2 2/2 HEATER GROUND CIRCUIT
Measure the resistance between the (K243) O2 2/2 Signal circuit and the (Z906) O2 2/2 Heater ground circuit in the O2 Sensor harness connector.
Is the resistance below 100 ohms?
Yes
No
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
No