DTC 1: Primary HO2S (Sensor 1) Circuit Malfunction Reset the ECM/PCM (see page 11-468). Start the engine. Hold the engine at 3,000 rpm (min-1) with no load (in Park or neutral) until the radiator fan comes on, then let it idle for at least one minute before test-driving. Test-drive under following conditions. in MT, A/T: 2nd position accelerate using wide open throttle for at least 5 seconds, then decelerate for at least 5 seconds with the throttle completely closed. Is the MIL on and does it indicate DTC 1? YES - Go to step 4. NO - Intermittent failure, system is OK at this time. Check for poor connections or loose wires at the primary HO2S (Sensor 1) and at the ECM/PCM. Inspect fuel pressure (see page 11-430). Is it normal? YES - Go to step 5. NO - Check for fuel supply system (see page 11-561). Let it idle for at least 1 minute before test-driving. Open the throttle wide open, then quickly release it. Measure voltage between ECM/PCM connector terminals A6 and A24. ECM/PCM CONNECTOR A (31P) Wire side of female terminals

Is the voltage above 0.6 V at wide open throttle to 4,500 rpm (min-1) and below 0.4 V when the throttle is quickly released from 4,500 rpm (min-1)? YES - Substitute a known-good ECM/PCM and recheck. If symptom/indication goes away, replace the original ECM/PCM. NO - Go to step 8. Turn the ignition switch OFF. Disconnect the primary HO2S (Sensor 1) 4P connector. At the Primary HO2S (Sensor 1) harness side, connect the battery positive terminal to terminal No. 4 and battery negative terminal to terminal No. 3). Start the engine. After 2 minutes, measure voltage between primary HO2S (Sensor 1) 4P connector terminals No. 1 and No. 2. ECM/PCM CONNECTOR A (31P) Wire side of female terminals Is the voltage above 0.6 V at wide open throttle to 4,500 rpm (min-1) and below 0.4 V when the throttle is quickly released from 4,500 rpm (min-1)? YES - Repair open or short in the wire between the ECM/PCM (A6) and the primary HO2S (Sensor 1). NO - Replace the primary HO2S (Sensor 1) (see page 11-554).