Check for continuity between the ECM/PCM connector terminal A1 and body ground. ECM/PCM CONNECTOR A (31P) Wire side of female terminals Is there continuity? YES - Repair short in the wire between the ECM/PCM (A1) and the primary HO2S (Sensor 1). NO - Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM. Measure voltage between the primary HO2S (Sensor 1) 4P connector terminal No. 4 and body ground. PRIMARY HO2S (SENSOR 1) 4P CONNECTOR Terminal side of male terminals Is there battery voltage? YES - Go to step 13. NO - Check the No. 4 ACG (10A) fuse in the under-dash fuse/relay box. If the fuse is OK, repair open in the wire between the primary HO2S (Sensor 1) and No. 4 ACG (10A) fuse.

Turn the ignition switch OFF. Reconnect the primary HO2S (Sensor 1) 4P connector. Disconnect ECM/PCM connector A (31P). Turn the ignition switch ON (II). Measure voltage between the ECM/PCM connector terminal A1 and A5. ECM/PCM CONNECTOR A (31P) Wire side of female terminals Is there 0.1 V or less? YES - Repair open in the wire between the ECM/PCM (A1) and the primary HO2S (Sensor 1). NO - Substitute a known-good ECM/PCM and recheck. If symptom/indication goes away, replace the original ECM/PCM.