Diagnostic Test

O2 SENSOR BELOW 2.52 VOLTS
1. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. With a scan tool, read the 1/2 O2 Sensor voltage.
Q: Is the voltage below 2.52 volts?

Yes :
- Go To 2
No :
- Refer to the INTERMITTENT CONDITION DIAGNOSTIC PROCEDURE .
- Perform the POWERTRAIN VERIFICATION TEST .
(K141) O2 1/2 SIGNAL CIRCUIT
1. Turn the ignition off.
2. Disconnect the 1/2 O2 Sensor harness connector.
3. Ignition on, engine not running.
4. With a scan tool, monitor the 1/2 O2 Sensor voltage.
Q: Is the O2 Sensor voltage above 4.8 volts?

Yes :
- Go To 3
No :
- Go To 5
O2 SENSOR

Fig 1: Checking O2 Sensor
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
1. Measure the voltage on the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Q: Is the voltage at 2.5 volts?

Yes :
- Replace the O2 Sensor.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Go To 4
(K904) O2 RETURN DOWNSTREAM CIRCUIT SHORTED TO GROUND

Fig 2: Checking O2 Return Upstream Circuit Shorted To Ground
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
1. Turn the ignition off.
2. Disconnect the C2 PCM harness connector.
3. Measure the resistance between ground and the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Q: Is the resistance below 100 ohms?

Yes :
- Repair the short to ground in the (K904) O2 Return Downstream circuit.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Go To 8
(K141) O2 1/2 SIGNAL CIRCUIT SHORTED TO GROUND

Fig 3: Checking O2 Sensor 1/1 Signal Circuit Shorted To Ground
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
1. Turn the ignition off.
2. Disconnect the C1 and C2 PCM harness connectors.
3. Measure the resistance between ground and the (K141) O2 1/2 Signal circuit in the O2 Sensor harness connector.
Q: Is the resistance below 100 ohms?

Yes :
- Repair the short to ground in the (K141) O2 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Go To 6
(K141) O2 1/2 SIGNAL CIRCUIT SHORTED TO THE (K904) O2 RETURN DOWNSTREAM CIRCUIT

Fig 4: Checking O2 Sensor 1/1 Signal Circuit Shorted To (K902) O2 Return Upstream Circuit
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
1. Measure the resistance between the (K141) O2 1/2 Signal circuit and the (K904) O2 Return Downstream circuit in the O2 Sensor harness connector.
Q: Is the resistance below 100 ohms?

Yes :
- Repair the short between the (K904) O2 Return Downstream circuit and the (K141) O2 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Go To 7
(K141) O2 1/2 SIGNAL CIRCUIT SHORTED TO THE (Z42) O2 1/2 HEATER GROUND CIRCUIT

Fig 5: Checking O2 Sensor 1/1 Signal Circuit Shorted To (Z43) O2 1/1 Heater Ground Circuit
Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
1. Measure the resistance between the (K141) O2 1/2 Signal circuit and the (Z42) O2 1/2 Heater ground circuit in the O2 Sensor harness connector.
Q: Is the resistance below 100 ohms?

Yes :
- Repair the short between the (Z42) O2 1/2 Heater ground circuit and the (K141) O2 1/2 Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Go To 8
PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
1. Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Q: Were there any problems found?

Yes :
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST .
No :
- Replace and program the Powertrain Control Module per Service Information.
- Perform the POWERTRAIN VERIFICATION TEST .