P0151

P0151-O2 SENSOR 2/1 CIRCUIT LOW






For a complete wiring diagram refer to: Electrical Diagrams

When Monitored
Engine running for less than 30 seconds and the O2 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 1.5 volts for 3 seconds after starting engine. One Trip Fault. Three good trips to turn off the MIL.

Possible Causes
- (K902) O2 UPSTREAM RETURN CIRCUIT SHORTED TO GROUND
- (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO GROUND
- (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO (K902) O2 UPSTREAM RETURN CIRCUIT
- (K43) O2 2/1 SIGNAL SHORTED TO THE (Z904) HEATER GROUND CIRCUIT
- O2 SENSOR
- PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.

Diagnostic Test
1. O2 SENSOR BELOW 1.5 VOLTS





Start the engine.
Allow the engine to reach normal operating temperature.
With a scan tool, read the 2/1 O2 Sensor voltage.

Is the voltage below 1.5 volts?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
2. (K43) O2 2/1 SIGNAL CIRCUIT
Turn the ignition off.
Disconnect the 2/1 O2 Sensor harness connector.
Ignition on, engine not running.
With a scan tool, monitor the 2/1 O2 Sensor voltage.

Is the O2 Sensor voltage above 4.8 volts?
Yes >> Go To 3
No >> Go To 5
3. O2 SENSOR





Measure the voltage on the (K902) O2 Upstream Return circuit in the O2 Sensor harness connector.

Is the voltage at 2.5 volts?
Yes >> Replace the 2/1 O2 Sensor.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 4
4. (K902) O2 UPSTREAM RETURN CIRCUIT SHORTED TO GROUND





Turn the ignition off.
Disconnect the PCM harness connectors.
Measure the resistance between ground and the (K902) O2 Upstream Return circuit in the O2 Sensor harness connector.

Is the resistance below 100 ohms?
Yes >> Repair the short to ground in the (K902) O2 Upstream Return circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 8
5. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO GROUND





Turn the ignition off.
Disconnect the PCM harness connectors.
Measure the resistance between ground and the (K43) O2 2/1 Signal circuit in the O2 Sensor harness connector.

Is the resistance below 100 ohms?
Yes >> Repair the short to ground in the (K43) O2 2/1 Signal circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 6
6. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO (K902) O2 UPSTREAM RETURN CIRCUIT





Measure the resistance between the (K43) O2 2/1 Signal circuit and the (K902) O2 Upstream Return circuit in the O2 Sensor harness connector.

Is the resistance below 100 ohms?
Yes >> Repair the short between the (K902) O2 Upstream Return circuit and the (K43) O2 2/1 Signal circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Go To 7
7. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO (Z904) HEATER GROUND CIRCUIT





Measure the resistance between the (K43) O2 2/1 Signal circuit and the (Z904) O2 Heater ground circuit in the O2 Sensor harness connector.

Is the resistance below 100 ohms?
Yes >> Repair the short between the (Z904) O2 Heater ground circuit and the (K43) O2 2/1 Signal circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test