PFI Chart A9 - Left O2 Sensor Lean Exhaust Signal
ECM provides a .45 volt reference to oxygen sensor on circuit No. 912. 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 signal voltage will toggle from rich to lean rapidly, at least one toggle every 2 seconds if ECM is in good control of air fuel mixture.
Fixed low oxygen sensor voltage readings are normally evidence that air/fuel mixture is lean and 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 oxygen sensor has failed and is giving an incorrectly low reading. However, if this is the case, closed loop fuel system will be overcompensating and causing rich operation (i.e, Black smoke, fouled spark plugs, poor fuel economy, high HC and CO, etc.) while the oxygen sensor is indicating lean.
Test Number 1) If Code EO17 is stored, DO NOT use this chart. See chart A7.
Test Number 2) With sensor disconnected, oxygen sensor reference voltage (.38-.63 volt) should appear. If ED32 reading is less than .38 volt then check for grounded signal circuit No. 912 or open ground circuit No. 413.
Test Number 3) Checks for sensor circuitry able to record rich readings. DVOM set on volts scale will provide a few billionths of an amp to drive circuit No. 912 greater than .64 volt (rich). Similar results may be obtained by placing one finger on battery positive terminal and another finger on oxygen sensor circuit No. 912 harness connector.
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, sensor can 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 volt to +.05 volt then ground is okay. If voltage is less than -.05 volt or greater than +.05 volt, repair poor connection between ECM pin B6 and oxygen sensor ground eyelet on front of right or rear engine cylinder head.
Test Number 5) If oxygen sensor circuit is okay, lean exhaust is caused by fuel/emissions system not controlling.
- Fuel delivery system not functioning properly may cause lean fuel mixture.
- If LEFT OXYGEN SENSOR TEST (chart A13) indicates sensor is okay, then check all connectors, terminals, etc., for an intermittent condition.
- Check for vacuum leaks at hoses, intake manifold and throttle body gaskets.
- Check for intermittent injector operation. See CHART A5.