Chart A-9 Left Oxygen Sensor Lean Exhaust Signal

PFI Chart A-9:

PFI Oxygen Sensor Circuit:

DESCRIPTION:

The PCM/ECM provides a 0.45 volt reference signal to the oxygen sensor on CKT 412. When warm, a properly operating oxygen sensor will drive the 0.45 volt reference lower (below 0.45 volts) to indicate a lean mixture and higher (above 0.45 volts) to indicate a rich mixture. The oxygen sensor signal voltage will swing from rich to lean rapidly, at least one swing every two seconds, if the PCM/ECM is in good control of the air/fuel mixture. Fixed Low oxygen sensor voltage readings are evidence that the air/fuel mixture is lean and 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 low reading. However If this is the case, the closed loop fuel system will overcompensate and cause a rich operation while the 02 sensor is indicating lean.

NOTES ON FAULT TREE:

1. If code E017 is stored, DO NOT USE this chart. See Chart A-6.

2. With the sensor disconnected, the oxygen sensor reference voltage (.38 to .63 volts) should appear. If the ED32 reading is less than .38 volts then check for grounded signal CKT 912 or open ground CKT 413.

3. Checking for sensor circuitry able to record rich readings. The DVOM set on volts will provide a few billionths of an amp to drive CKT 912 to above .64 volts (rich). Similar results may be obtained by placing one finger on the battery positive terminal and another finger on the oxygen sensor CKT 912, harness terminal.

4. The PCM/ECM compares oxygen sensor signal voltage received on CKT 912 to the ground voltage on CKT 413. If the PCM/ECM doesn't have a good ground to the engine on CKT 413, the oxygen sensor can appear falsely high or low. With the engine running, use a voltmeter to measure voltage from the oxygen sensor at the exhaust manifold to pin B6 at the PCM/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 connection between PCM/ECM pin B6 and oxygen sensor ground eyelet on front of right or rear engine cylinder head.

5. If the oxygen sensor circuit is OK, then lean exhaust is caused by fuel emissions systems not controlling:

a. A fuel delivery system which is not functioning properly may cause a lean fuel mixture . This malfunction scan be caused by fuel pressure less than 40 psi at the injectors, by defective injectors, etc. refer to the Fuel System diagnosis Chart A-4, for additional information.

b. If the left oxygen sensor test Chart A-13 indicates that the sensor is OK, then check all connectors, terminals, etc., for an intermittent condition.

c. Check for vacuum leaks at hoses, intake manifold and throttle body gaskets.

d. Check for intermittent injector operation see Chart A-5.