Oxygen (O2) Sensor Circuit Check
WARNING: This page is about a different car, the 1989 Cadillac Fleetwood and 1989 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
When the ECM sees that the oxygen sensor voltage is varying from the normal cold reading of .45 volt and the coolant sensor value is greater than 185°F (85°C), ECM will place system in closed loop. In closed loop, ECM will adjust fuel delivery rate based upon oxygen sensor readings.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- The ECM compares voltage on circuit No. 412 to the ground voltage on circuit No. 413. It is essential that the oxygen sensor ground and ECM ground on terminal A1 show good continuity.
- At key on with oxygen sensor disconnected, the parameter P.0.7 should read .45 volt. Lower or higher voltage indicates circuit problems.
- At this point, the oxygen sensor circuit between the 2-way connector and the ECM, all of the oxygen sensor grounds, and the ECM are all functioning correctly and have good contact.
- This series of tests will determine if a faulty reading is due to poor ground connections, circuit fault or problem with the ECM connection of ECM.