For a complete wiring diagram Refer to Section 8W.This diagnostic provides a continuous check of the O2 heater circuit during operation. The heater circuit is momentarily disabled to allow a resistance measurement to be taken to infer heater temperature. The current delivery to the heater is duty cycled to maintain a specific target temperature. The error from the target temperature is continuously monitored to assess heater performance.When Monitored:Engine running and heater duty cycle greater than 0%. Battery voltage greater than 11.0 volts.Set Condition:No sensor output is received when the PCM powers up the sensor heater. Two trip fault. Three good trips to turn off the MIL.Possible Causes(K99) O2 1/1 HEATER CONTROL CIRCUIT OPEN(Z906) O2 1/1 HEATER GROUND CIRCUIT OPENO2 SENSORPCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. O2 SENSOR HEATER OPERATIONTurn the ignition off.Wait a minimum of 8 minutes to allow the O2 Sensor to cool down before continuing the test. Allow the O2 Sensor voltage to stabilize between 4.6 and 5.0 volts.Ignition on, engine not running.With a scan tool, actuate the O2 Heater Test.With the scan tool, monitor 1/1 O2 Sensor voltage for at least 2 minutes.Does the voltage stay above 4.5 volts?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 2. O2 SENSOR HEATER ELEMENTTurn the ignition off.Allow the O2 sensor to cool down to room temperature.Disconnect the O2 Sensor harness connector.Measure the resistance of the O2 Heater Element across the 1/1 O2 Sensor connector between the O2 Heater Control terminal and the Heater ground terminal.O2 Heater Element resistance values should be measured at 70°F (21.1°C). The resistance value will vary with different temperature values.Is the resistance of the O2 Sensor Heater Element between 2.0 and 30.0 ohms?YesGo To 3NoReplace the O2 Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 3. (K99) O2 1/1 HEATER CONTROL CIRCUIT OPEN

Disconnect the C2 PCM harness connector.Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.Measure the resistance of the (K99) O2 1/1 Heater Control circuit from the O2 harness connector to the appropriate terminal of special tool #8815.Is the resistance below 0.5 of an ohm?YesGo To 4NoRepair the excessive resistance in the (K99) O2 1/1 Heater Control circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 4. (Z906) O2 1/1 HEATER GROUND CIRCUIT OPEN

Measure the resistance between ground and the (Z906) O2 1/1 Heater ground circuit in the O2 Sensor harness connector.Is the resistance below 0.5 of an ohm?YesGo To 5NoRepair the excessive resistance in the (Z906) O2 1/1 Heater ground circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 5. 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)