Diagnostic Procedures

Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.

NOTE: If any DTCs are set, except HO2S DTCs, refer to those DTCs before proceeding with this diagnostic procedure. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

Verify that the engine is at the operating temperature. Operate engine above 1200 RPM for 2 minutes. With a scan tool, observe the HO2S voltage parameter. Does scan tool indicate HO2S voltage varying outside 400-500 mV? If yes, go to next step. If no, go to step 4.
Operate the vehicle within Failure Records conditions. Does the scan tool indicate this DTC failed this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
Inspect and test for the following conditions:
- Exhaust leak.
- Correctly installed HO2S.
- Damaged wiring.
Did you find and correct the condition? If yes, go to step 15. If no, go to next step.
Turn ON the ignition, with the engine OFF. Disconnect the HO2S. Jumper the HO2S high signal circuit, PCM side, to a good ground. With a scan tool, observe HO2S voltage parameter. Does the scan tool indicate HO2S voltage more than 400 mV? If yes, go to next step. If no, go to step 10.
Remove the jumper wire. Measure the voltage on the HO2S high signal circuit, PCM side, using a DMM connected to a ground. Does the voltage measure near 4.5 V? If yes, go to next step. If no, go to step 9.
Measure the voltage on the HO2S low signal circuit, PCM side, using a DMM connected to a ground. Does the voltage measure near 5 V? If yes, go to step 11. If no, go to next step.
Test the HO2S low signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 15. If no, go to step 13.
Test the HO2S high signal circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 15. If no, go to step 13.
Inspect the low signal circuit for a short to ground. Did you find and correct the condition? If yes, go to step 15. If no, go to step 14.
Test for poor connections at the HO2S. Did you find and correct the condition? If yes, go to step 15. If no, go to next step.

NOTE: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a White powdery coating. Silicone contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor. Determine the cause of contamination before replacing the sensor.

Inspect and test for the following:
- Fuel contamination.
- Excess engine oil or coolant consumption.
Replace the affected HO2S sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step 15.
Inspect for poor connections at the PCM. Did you find and correct the condition? If yes, go to step 15. If no, go to next step.
Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step 2.
Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.