Action Taken
- ECM turns on "ENGINE CONTROL SYSTEM FAULT" light.
- ECM commands BCM to display. "SERVICE SOON" message on DIC.
- ECM uses the left O2 sensor signal to control the amount of fuel delivered unless code EO17, EO42 or EO43 is set. If any codes are set, closed loop will be disabled.
The ECM provides a .45-volt reference to oxygen sensor on circuit No. 412. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (below .45 volts) to indicate lean mixtures and higher (above .45 volts) to indicate a rich mixture. If under the above test conditions the oxygen sensor does not vary, the ECM assumes that the sensor can not respond to air/fuel mixtures whether they are rich or lean. Code EO13 is then set.
NOTE:
The following step numbers refer to circled numbers on diagnostic chart. See Fig 1
. For circuit identification, see Fig 2
.
- At key on with oxygen sensor disconnected, the parameter ED33 should read .38-.57 volts Lower or higher voltage indicates circuit problems.
- The ECM compares voltage on circuit No. 412 to ground voltage on circuit No. 413. It is essential that the oxygen sensor ground and ECM ground on pin "E15" show good continuity (no voltage difference) with engine running.