Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Diagnostic Test
- 1) 2/2 OXYGEN SENSOR HEATER CONTROL OPERATION NOTE: Allow the sensor to cool to ambient temperature before continuing. The voltage should stabilize between 4.6 and 5.0 volts.
Turn the ignition on.
With a scan tool, perform the 2/2 O2 Sensor Heater Test.
With the scan tool, monitor the 2/2 Oxygen Sensor voltage for at least 2 minutes.
Does the voltage stay above 4.5 volts?
Yes
- Go to 2).
No
- Refer to *CHECKING FOR AN INTERMITTENT DTC .
- 2) 2/2 OXYGEN SENSOR
Turn the ignition off.
NOTE: Allow the sensor to cool to ambient temperature before continuing. The voltage should stabilize between 4.6 and 5.0 volts.Disconnect the 2/2 Oxygen Sensor harness connector.
Measure the resistance of the O2 sensor heater element across the 2/2 Oxygen Sensor connector between the heater control terminal and the ground terminal.
NOTE: The resistance of the heater element will vary according to temperature and should be measured at 70° F (21.1° C).Is the resistance between 2.0 and 30.0 ohms?
Yes
- Go to 3).
No
- Replace the 2/2 Oxygen Sensor in accordance with the Service Information.
- Perform *PCM VERIFICATION TEST .
- 3) (K399) O2 2/2 HEATER CONTROL CIRCUIT OPEN OR HIGH RESISTANCE
Disconnect the Powertrain Control Module (PCM) harness connector.
CAUTION: 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 (K399) O2 2/2 Heater Control circuit between the 2/2 Oxygen Sensor harness connector and the appropriate terminal of special tool #8815.
Is the resistance below 0.5 ohms?
Yes
- Go to 4).
No
- Repair the (K399) O2 2/2 Heater Control circuit for an open circuit or high resistance.
- Perform *PCM VERIFICATION TEST .
- 4) (Z902) GROUND CIRCUIT OPEN OR HIGH RESISTANCE
Using a 12 volt test light connected to 12 volts, check the (Z902) Ground circuit in the 2/2 Oxygen Sensor harness connector.
NOTE: The test light should be illuminated and bright. Compare the brightness to that of a direct connection to the battery.Is the test light illuminated and bright?
Yes
- Go to 5).
No
- Repair the (Z902) Ground circuit for an open circuit or high resistance.
- Perform *PCM VERIFICATION TEST .
- 5) POWERTRAIN CONTROL MODULE (PCM)
Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the 2/2 Oxygen Sensor and the Powertrain Control Module (PCM).
Look for any chafed, pierced, pinched, or partially broken wires.
Look for broken, bent, pushed out or corroded terminals.
Refer to any Technical Service Bulletins that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform *PCM VERIFICATION TEST .
No
- Replace and program the Powertrain Control Module (PCM) in accordance with the Service Information.
- Perform *PCM VERIFICATION TEST .
Use the Manual With the Right Hardware
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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