Chart A8 - Rich Exhaust Signal
The ECM provides a .45-volt reference signal to oxygen sensor on circuit No. 412. When oxygen sensor is cold (less than 200°C), output voltage will be about 0.5 volt, the ECM will keep system in open loop operation. When warm, a properly operating oxygen sensor will drive the .45-volt reference lower (less than .45 volt) to indicate a lean mixture and higher (greater than .45 volt) to indicate a rich mixture.
The oxygen sensor signal voltage will swing from rich to lean rapidly (one swing every 2 seconds), if ECM is in control of air/fuel mixture. Fixed high oxygen sensor voltage readings are normally evidence that air/fuel mixture is rich and closed loop system is unable to compensate sufficiently due to a failure in some part of engine emission or fuel systems.
Less likely is the possibility that the oxygen sensor has failed and is giving an incorrectly high reading. If the oxygen sensor is giving false rich readings, the closed loop fuel system will be overcompensating and causing lean operation while oxygen sensor is indicating rich.
- If Code EO13 is stored, DO NOT use this chart. See CHART A6 - OXYGEN SENSOR NOT READY.
- With sensor disconnected, oxygen sensor reference voltage (.38-.63 volt) should appear. If parameter ED07 reading is greater than .64 volt, check for circuit No. 412 shorted to voltage or poor ground on circuit No. 413B.
- Check for oxygen sensor and ECM's ability to record lean readings. The ECM compares oxygen sensor signal voltage received on circuit No. 412 to ground voltage on circuit No. 413B. If ECM does not have a good ground to engine on circuit No. 413B, oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from oxygen sensor at exhaust manifold to terminal A1 at ECM. If voltage is -.05 volt to +.05 volt, the ground circuit is okay. If voltage is less than -.05 volt or more than +.05 volt, repair poor ground circuit connection between ECM terminal A1 and oxygen sensor ground eyelet on engine, at rear bank of cylinders, with a ground eyelet on power steering line retainer clip.
- If oxygen sensor circuit is okay, rich exhaust is caused by fuel or emission systems not controlling the following:
- A restricted air cleaner could cause a rich fuel mixture. Inspect air cleaner and replace if necessary.
- A fuel delivery system which is not functioning properly may cause a rich fuel mixture. This malfunction can be caused by fuel pressure which is greater than 12 psi at injectors or by defective injectors. See CHART A4A - FUEL SYSTEM DIAGNOSIS.
- Excessive EGR flow displaces oxygen and causes a rich exhaust indication. See CHART A5 - INJECTION SYSTEM DIAGNOSIS.
- Injector dripping or injector leaks can cause rich exhaust. See CHART A5 - INJECTION SYSTEM DIAGNOSIS to check injectors.
- Fuel evaporation (carbon) canister loaded with fuel can cause rich operation. See CHART C3 - CANISTER PURGE DIAGNOSIS.
- Vacuum leak to MAP hose can cause a false high MAP reading. High MAP readings cause ECM to deliver too much fuel for current driving conditions. See Code EO34 chart to diagnose.
- If CHART A9 - OXYGEN SENSOR DIAGNOSIS indicates that sensor is okay, check all connectors and terminals for an intermittent code.