PFI Chart A11 - Left O2 Sensor Rich Exhaust Signal
ECM provides a .45 volt reference to oxygen sensor on circuit No. 412. When warm, a properly operating oxygen sensor will drive .45 volt reference lower (less than .45 volt) to indicate lean mixture and higher (greater than .45 volt) to indicate rich mixture.
Oxygen sensor voltage readings which remain either high or low are normally evidence that the closed loop system is unable to compensate sufficiently due to a failure in some part of engine emission or fuel system.
Less likely is the possibility that the oxygen sensor has failed and is giving an incorrect high or low voltage reading. However, if this is the case, closed loop fuel system will be overcompensating and causing rich operation while oxygen sensor is indicating lean readings. Likewise, 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.
Test Number 1) If Code EO17 is stored, DO NOT use this chart, see PFI CHART A7.
Test Number 2) With sensor disconnected, oxygen sensor reference voltage (.38-.63 volt) should appear. If ED33 reading is greater than .64 volt check circuit No. 912 for short to voltage or poor ground on circuit No. 912.
Test Number 3) Checks for oxygen sensor and ECM ability to record lean readings.
Test Number 4) ECM compares oxygen sensor signal voltage received on circuit No. 912 to ground voltage on circuit No. 413. If ECM doesn't have a good ground to engine on circuit No. 413, oxygen sensor may appear falsely high or low. With engine running, use voltmeter to measure voltage from oxygen sensor at exhaust manifold to pin E15 at ECM. If voltage is -.05 to +.05 volt then ground is okay. If voltage is less than -.05 volt or greater than +.05 volt, repair poor ground connection between ECM terminal B6 and oxygen sensor ground on (right) rear cylinder head, front of engine.
Test Number 5) If oxygen sensor circuits are okay, rich exhaust is caused by fuel/emissions system not controlling.
- Restricted air cleaner could cause rich fuel mixture. Inspect air cleaner and replace if necessary.
- Fuel delivery system which is not functioning properly may cause rich fuel mixture. This can be caused by fuel pressure which is greater than 45 psi at injectors, by defective injectors, etc. Also check for vacuum not present at fuel pressure regulator. Fuel pressure should vary with engine load.
- Injector dripping or injector leaks and cause rich exhaust.
- Carbon canister loaded with fuel can cause rich operation.
- Vacuum leak to MAP sensor can cause false high MAP sensor readings. High MAP sensor readings cause ECM to deliver to much fuel for current driving conditions.
- If LEFT OXYGEN SENSOR DIAGNOSIS CHART A13 indicates that sensor is okay, then check all connections, terminals, etc., for intermittent condition.