Action Taken
- ECM turns on "ENGINE CONTROL SYSTEM FAULT" light.
- ECM commands BCM to display "SERVICE NOW" message on DIC.
- ECM turns off canister purge and air management solenoids.
- ECM uses right O2 sensor information for air/fuel computations.
The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold (below 392°F/200°C), output voltage will be about .45 volts and ECM will keep system in open loop operation. When warm, a properly operating oxygen sensor will drive the .45 volt reference lower (below .45 volts) to indicate a rich mixture. Oxygen sensor signal voltage will swing from rich to lean rapidly. This will occur at least one swing every 2 seconds if ECM is in good control of air-fuel mixture.
When ECM sees that oxygen sensor signal is not at cold voltage of .45 volts, it will send system into closed loop operation. In closed loop operation, ECM will meter fuel into engine based on oxygen sensor readings.
Code EO43 is set when right oxygen sensor stays at rich voltage for more than 50 seconds during test conditions. Code EO43 will also set when:
- Oxygen sensor circuitry has faults.
- When air-fuel ratio is actually rich due to fuel control or emissions system fault.
- With oxygen sensor disconnected, parameter ED32 should remain at reference voltage (.38-.63 volts).
- Checks for ECM ability to recognize lean oxygen sensor input.
- The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413. If ECM does not have a good ground to engine on circuit No. 413, oxygen sensor can appear falsely high or low.
With engine running, use a voltmeter to measure voltage from oxygen sensor pin "A" at exhaust manifold to ECM terminal "136". If the voltage less than -.05 volts or greater than +.05 volts, repair the ground on circuit No. 413 between ECM terminal "B6" and ground.