Test Procedures

Turn ignition on and connect scan tool to data link connector. Verify DTC P0133 or P0134 is set. If DTC P0135 is also set, repair DTC P0135 first. See DTC P0135 OR P0141: HO2S HEATER CIRCUIT MALFUNCTION .
Start engine and allow to idle at normal operating temperature. Increase engine speed to 4000 RPM. Using scan tool, monitor HO2S voltage. If voltage is zero volts, go to next step. If voltage is constant and approximately 450 mV, go to step 4 . If voltage varies, but stays less than 500 mV (lean), go to step 6 . If voltage varies, but stays more than 500 mV (rich), go to step 7 . If voltage varies between 100 and 900 mV, go to step 8 . If voltage is constant and approximately 5.0 volts or 12.0 volts, repair short to voltage in wiring harness. When repairs are completed, clear DTCs and verify HO2S operation.
Disconnect front HO2S 4-pin connector. If DTC P0133 is set, voltage displayed on scan tool should be approximately 450 mV. If DTC P0134 is set, voltage displayed on scan tool should be approximately 50 mV. If voltage is as specified, replace HO2S. If voltage is not as specified, repair short to ground in Orange/Black wire between HO2S connector terminal No. 1 and ECM 81-pin connector terminal No. 36. When repairs are completed, clear DTCs and verify HO2S operation.
While engine is operating, backprobe between front HO2S 4-pin connector terminals No. 1 and No. 2, and measure voltage. If voltage changes from less than 500 mV to more than 500 mV, go to next step. If voltage does not change, replace HO2S. When repairs are completed, clear DTCs and verify HO2S operation.
Turn ignition off. Disconnect front HO2S 4-pin connector and ECM 81-pin connector. Using a jumper wire, connect HO2S connector terminal No. 1 to ground. Measure resistance between ground and ECM connector terminal No. 36 (Orange/Black wire). If resistance is one ohm or less, ensure ECM connector terminals are clean and tight. Clear DTCs and verify HO2S operation. If problem persists, replace ECM. If resistance is more than one ohm, repair open or cause of high resistance in circuit between HO2S and ECM. When repairs are completed, clear DTCs and verify HO2S operation.
If voltage varies and is always less than 500 mV (lean), check air inlet downstream of Mass Airflow (MAF) sensor for leaks or damage. Check exhaust manifold for cracks or leaks. If any leaks or damage are found perform repairs as necessary. Replace exhaust manifold if necessary. If no leaks or damage are found, go to next step.
Perform fuel pressure inspection. See FUEL PRESSURE TEST under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pressure is within specification and no pressure leak-down is detected, go to next step. If fuel pressure is not as specified, repair fuel system as necessary. When repairs are completed, clear DTCs and verify HO2S operation.
Turn ignition off. Disconnect ignition coil connector. Connect voltmeter between negative battery cable and cable attachment located on engine. Measure voltage drop across negative battery cable while cranking engine. If voltage drop is less than 0.5 volt, go to next step. If voltage drop is more than 0.5 volt, replace negative battery cable. When repairs are completed, clear DTCs and verify HO2S operation.
Disconnect negative battery cable and measure resistance between generator housing and engine ground point. If resistance is one ohm or less, go to next step. If resistance is more than one ohm, clean mating surfaces of generator housing and engine. When repairs are completed, clear DTCs and verify HO2S operation.
If MIL is illuminating intermittently and DTC P0133 is set, problem is most likely a poor ground circuit. Clean negative battery terminal and engine ground. In addition, clean mating surfaces of generator housing and engine. If MIL was illuminated and DTC P0133 or P0134 is set, replace front HO2S. When repairs are completed, clear DTCs and verify HO2S operation.