PFI Chart A-11: Left O2 Sensor Rich: Description
The ECM provides a .45 volt reference signal to the oxygen sensor on CKT 412. When warm, a properly operating oxygen sensor will drive the .45 volt reference lower (below .45 volts) to indicate a lean mixture and higher (above .45 volts) to indicate a rich mixture.
The oxygen sensor signal voltage will toggle from rich to lean rapidly, at least one toggle every two seconds, if the ECM is in good control of the air fuel mixture. Fixed high oxygen sensor voltage readings are normally evidence that the air-fuel mixture is rich and the closed loop system is unable to compensate sufficiently due to a failure in some part of the engine emission or fuel system. 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 the O2 sensor is indicating rich.
- If code EO17 is stored do not use this chart, go to PFI CHART A-7: LEFT O2 SENSOR NOT READY .
- With the sensor disconnected, the oxygen sensor reference voltage (.38 to .63 volts) should appear. If the ED32 reading is greater than .64 volts then check for CKT 412 shorted to voltage or poor ground on CKT 412.
- Checking for oxygen sensor and ECM able to record lean readings.
- The ECM compares oxygen sensor signal voltage received on CKT 412 to the ground voltage on CKT 413. If the ECM doesn't have a good ground to the engine on CKT 413, the oxygen sensor can appear falsely high or low. With engine running, use a voltmeter to measure voltage from the oxygen sensor at the exhaust manifold to Pin B6 at the ECM. If the voltage is -.05 volts to +.05 volts then the ground is OK. If the voltage is less than -.05 volts or greater than +.05 volts; repair poor ground connection between ECM terminal B6 and oxygen sensor ground on the (right) rear cylinder head, front of engine.
- If the oxygen sensor circuit is OK, the rich exhaust is caused by fuel/emissions system not controlling.
- A restricted air cleaner could cause a rich fuel mixture. Inspect the 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 45 Psi at the injectors, by defective injectors, etc. Refer to PFI CHART A-4A: STATIC FUEL PRESSURE DIAGNOSIS for additional information. Also check for vacuum at the fuel pressure regulator. Fuel pressure should vary with engine load.
- Injector dripping or injector leaks can cause rich exhaust. To check injectors, see PFI CHART A-5: INJECTOR SYSTEM DIAGNOSIS .
- Carbon canister loaded with fuel can cause rich operation, see PFI CHART C-3: CANISTER PURGE CONTROL DIAGNOSIS .
- Vacuum leak to the MAP sensor can cause a false high MAP reading. High MAP readings cause the ECM to deliver too much fuel for current driving conditions. See Code EO34, "Notes On Intermittents " to diagnose.
- If the "Left Oxygen Sensor Diagnosis", (PFI CHART A-13: LEFT O2 SENSOR DIAGNOSIS ) indicates that the sensor is OK, then check all connectors, terminals, etc. for an intermittent condition.