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.
DTC P1172: A/F Sensor (Sensor 1) Circuit Out of Range High
- Turn the ignition switch to ON (II).
- Clear the DTC with the HDS.
- Start the engine. Hold the engine speed at 3,000 RPM without load (in neutral) until the radiator fan comes on, then let it idle.
- Monitor the OBD STATUS for DTC P1172 in the DTCs MENU with the HDS.
Does the screen indicate FAILED?
YES -Go to step 5.
NO -If the screen indicates PASSED, intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at the A/F sensor (Sensor 1) and the ECM. If the screen indicates EXECUTING, keep idling until a result comes on. If the screen indicates OUT OF CONDITION, go to step 3 and recheck.
- Turn the ignition switch to LOCK (0).
- Replace the A/F sensor (Sensor 1) (see A/F SENSOR REPLACEMENT ).
- Turn the ignition switch to ON (II).
- Reset the ECM with the HDS.
- Do the ECM idle learn procedure (see ECM IDLE LEARN PROCEDURE ).
- Start the engine. Hold the engine speed at 3,000 RPM without load (in neutral) until the radiator fan comes on, then let it idle.
- Check for Temporary DTCs or DTCs with the HDS.
Is DTC P1172 indicated?
YES -Check for poor connections or loose terminals at the A/F sensor (Sensor 1) and the ECM, then go to step 1.
NO -Go to step 12.
- Monitor the OBD STATUS for DTC P1172 in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES -Troubleshooting is complete. If any other Temporary DTCs or DTCs were indicated in step 11, go to the indicated DTC's troubleshooting.
NO -If the screen indicates FAILED, check for poor connections or loose terminals at the A/F sensor (Sensor 1) and the ECM, then go to step 1. If the screen indicates EXECUTING, keep idling until a result comes on. If the screen indicates OUT OF CONDITION, go to step 10.
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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.