Chart A9 - Oxygen (O2) Sensor Diagnosis
NOTE:
The following step numbers refer to the numbers in the accompanying flow chart(s).
- With engine running warm (coolant temperature 185°F/85°C or greater) and at fast idle, observe engine data parameter ED07.
- While running engine at fast idle, observe open/closed loop status light, and auto annunciator in CCDIC. If ECM switches system to closed loop operation, the oxygen sensor is okay. If ECM remains in open loop operation, coolant temperature ("ED04") is above 185°F (85°C), and ECM and harness have previously been verified in CHART A6, replace oxygen sensor.
- If voltage remains between .30 .60 volts for a minimum of one minute, check for the possibility of leaded or contaminated fuel. Check before checking for a faulty oxygen sensor connection or a faulty oxygen sensor, as leaded fuel can damage catalytic converter and oxygen sensor.
- If there is no voltage variation and if ECM and harness are operating properly as previously verified by CHART A6 - OPEN LOOP DIAGNOSIS, check for faulty oxygen sensor.
NOTE:
This chart assumes that "DFI System Check" and Chart A-6 "Open Loop Diagnosis" have both been performed to verify that the ECM and oxygen sensor wiring are operating properly.