P0137

P0137-O2 SENSOR 1/2 CIRCUIT LOW





For a complete wiring diagram, refer to the Wiring Information.

Theory of operation

The Oxygen Sensors (O2 Sensor) are used for fuel control and catalyst monitoring. Each O2 Sensor compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Powertrain Control Module (PCM) operates in an Open Loop mode, ignoring the O2 Sensor signal voltage while calculating the air-to-fuel ratio. The heating elements inside each O2 Sensor heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the PCM to calculate the air-to-fuel ratio sooner. While the engine runs, the O2 Sensor heats up and begins to generate a voltage within a range of 0-1,275 mV. Once sufficient O2 Sensor voltage fluctuation is observed by the PCM, Closed Loop is entered. The PCM uses the O2 sensor voltage to determine the air-to-fuel ratio. An O2 Sensor voltage that increases toward 1,000 mV indicates a rich fuel mixture. An O2 Sensor voltage that decreases toward 0 mV indicates a lean fuel mixture.

- 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 Powertrain Control Module (PCM) detects that the O2 Sensor 1/2 signal voltage is below minimum acceptable value. The DTC will set as Pending after one trip and Active after two trips. Three good trips to turn off the MIL.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)
1. Turn the ignition on.
2. With the scan tool, read DTCs. Record DTC and Freeze Frame information.
3. Start the engine and allow it to idle for at least 60 seconds.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

4. With the scan tool, read the active DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test

2. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT
1. Turn the ignition off.
2. Disconnect the O2 Sensor 1/2 harness connector.
3. Ignition on, engine not running.
4. With the scan tool, monitor the O2 Sensor 1/2 voltage.

Is the O2 Sensor 1/2 voltage between 4.1 and 5.0 Volts?

Yes

- Go To 3

No

- Go To 5

3. O2 SENSOR




1. Measure the voltage on the (K904) O2 Sensor 1/2 Return circuit in the O2 Sensor 1/2 harness connector.

Is the voltage at 2.5 Volts?

Yes

- Verify that there is good pin to terminal contact in the O2 Sensor 1/2 and Powertrain Control Module connectors. If OK, replace the O2 Sensor 1/2. Oxygen Sensor - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 4

4. (K904) O2 SENSOR 1/2 RETURN CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance between ground and the (K904) O2 Sensor 1/2 Return circuit in the O2 Sensor 1/2 harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short to ground in the (K904) O2 Sensor 1/2 Return circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

5. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the PCM C2 harness connector.
3. Measure the resistance between ground and the (K141) O2 Sensor 1/2 Signal circuit in the O2 Sensor 1/2 harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short to ground in the (K141) O2 Sensor 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 6

6. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT SHORTED TO THE (K904) O2 SENSOR 1/2 RETURN CIRCUIT




1. Measure the resistance between the (K141) O2 Sensor 1/2 Signal circuit and the (K904) O2 Sensor 1/2 Return circuit in the O2 Sensor 1/2 harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short between the (K904) O2 Sensor 1/2 Return circuit and the (K141) O2 Sensor 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 7

7. (K141) O2 SENSOR 1/2 SIGNAL CIRCUIT SHORTED TO THE O2 SENSOR 1/2 HEATER GROUND CIRCUIT




1. Measure the resistance between the (K141) O2 Sensor 1/2 Signal circuit and the O2 Sensor 1/2 Heater ground circuit in the O2 Sensor 1/2 harness connector.

Is the resistance below 100 Ohms?

Yes

- Repair the short between the O2 Sensor 1/2 Heater ground circuit and the (K141) O2 Sensor 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 8

8. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Oxygen Sensor 1/2 and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Oxygen Sensor 1/2 and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module. Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.