For a complete wiring diagram Refer to Section 8W.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 2.5196 volts for 3 seconds after starting engine. Two Trip Fault. Three good trips to turn off the MIL.Possible Causes(K902) O2 RETURN UPSTREAM CIRCUIT SHORTED TO GROUND(K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO GROUND(K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO THE (K902) O2 RETURN UPSTREAM CIRCUIT(K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO THE (Z906) HEATER GROUND CIRCUITO2 SENSORPCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. O2 SENSOR BELOW 2.52 VOLTSStart 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 2.52 volts?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 2. (K43) O2 2/1 SIGNAL CIRCUITTurn 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?YesGo To 3NoGo To 53. O2 SENSOR

Measure the voltage on the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.Is the voltage at 2.5 volts?YesReplace the 2/1 O2 Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 44. (K902) O2 RETURN UPSTREAM CIRCUIT SHORTED TO GROUND

Turn the ignition off.Disconnect the C2 PCM harness connector.Measure the resistance between ground and the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.Is the resistance below 100 ohms?YesRepair the short to ground in the (K902) O2 Return Upstream circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 85. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO GROUND

Turn the ignition off.Disconnect the C2 PCM harness connector.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?YesRepair the short to ground in the (K43) O2 2/1 Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 66. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO THE (K902) O2 RETURN UPSTREAM CIRCUIT

Measure the resistance between the (K43) O2 2/1 Signal circuit and the (K902) O2 Return Upstream circuit in the O2 Sensor harness connector.Is the resistance below 100 ohms?YesRepair the short between the (K902) O2 Return Upstream circuit and the (K43) O2 2/1 Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 77. (K43) O2 2/1 SIGNAL CIRCUIT SHORTED TO THE (Z906) HEATER GROUND CIRCUIT

Measure the resistance between the (K43) O2 2/1 Signal circuit and the (Z906) O2 Heater ground circuit in the O2 Sensor harness connector.Is the resistance below 100 ohms?YesRepair the short between the (Z906) O2 Heater ground circuit and the (K43) O2 2/1 Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 88. PCMBefore 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?YesRepair as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoReplace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)