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
- DTC IS ACTIVE
- Start the engine and allow it to reach normal operating temperature.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.
- With the scan tool, select View DTCs.
Is the status Active for this DTC?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Refer to INTERMITTENT CONDITION .
- Start the engine and allow it to reach normal operating temperature.
- (K99) O2 SENSOR 1/1 HEATER CONTROL CIRCUIT OPEN OR HIGH RESISTANCE
- Turn the ignition off.
- Disconnect the Oxygen Sensor 1/1 harness connector.
- Disconnect the Powertrain Control Module (PCM) C2 harness connector.
- Measure the resistance of the (K99) O2 Sensor 1/1 Heater Control circuit between the Oxygen Sensor 1/1 harness connector and the Powertrain Control Module (PCM) C2 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 3
No
- Repair the (K99) O2 Sensor 1/1 Heater Control circuit for an open circuit or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
- (Z904) GROUND CIRCUIT OPEN OR HIGH RESISTANCE
- Measure the resistance between battery (-) and the (Z904) Ground circuit in the O2 Sensor harness connector.NOTE:
A good chassis ground can also be used in place of the battery (-).
Is the resistance below 5.0 Ohms?
Yes
- Go To 4
No
- Repair the excessive resistance in the (Z904) Ground circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
- Measure the resistance between battery (-) and the (Z904) Ground circuit in the O2 Sensor harness connector.
- OXYGEN SENSOR 1/1
- Connect the Powertrain Control Module (PCM) C2 harness connector.
- Turn the ignition on.
- With the scan tool, actuate the Oxygen Sensor 1/1 control to the maximum allowable percentage.
- Using a 12-volt test light connected to ground, check the (K99) O2 Sensor 1/1 Heater Control circuit in the Oxygen Sensor 1/1 harness connector.NOTE:
The test light should flash dimly.
- With the scan tool, actuate the Oxygen Sensor 1/1 control to the OFF (0%) position.
- Using a 12-volt test light connected to ground, check the (K99) O2 Sensor 1/1 Heater Control circuit in the Oxygen Sensor 1/1 harness connector.NOTE:
The test light should not be illuminated.
Does the test light flash dimly with the actuator ON (25%) and not illuminated with the actuator OFF (0%)?
Yes
- Replace the Oxygen Sensor 1/1 in accordance with the Service Information. Refer to SENSOR, OXYGEN, REMOVAL .
- Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
No
- Go To 5
- POWERTRAIN CONTROL MODULE (PCM)
- Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Oxygen Sensor 1/1 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.
- Perform any Technical Service Bulletins (TSBs) that may apply.
Were any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
No
- Replace and program the Powertrain Control Module (PCM) in accordance with the Service Information. Refer to MODULE, POWERTRAIN CONTROL, REMOVAL .
- Perform the POWERTRAIN VERIFICATION TEST. Refer to POWERTRAIN VERIFICATION TEST .
NO RELATED
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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.