- Check for continuity between ECM connector terminal A1 and body ground.
ECM CONNECTOR A (31P)
Wire side of female terminals
Is there continuity?
YES - Repair short in the wire between the ECM (A1) and the primary HO2S (Sensor 1). 
NO - Substitute a known-good ECM and recheck (see page 11-5). If symptom/indication goes away, replace the original ECM.
- Measure voltage between the primary HO2S (Sensor 1) 4P connector terminal No. 3 and body ground.
PRIMARY HO2S (SENSOR 1) 4P CONNECTOR
Wire side of female 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 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 connector A (31P).
- Turn the ignition switch ON (II).
- Measure voltage between ECM connector terminal A1 and A5.
ECM CONNECTOR A (31P)
Wire side of female terminals
Is there 0.1 V or less?
YES - Repair open in the wire between the ECM (A1) and the primary HO2S (Sensor 1).
NO - Substitute a known-good ECM and recheck (see page 11-5). If symptom/indication goes away, replace the original ECM.