Chart A-11 Left Oxygen Sensor Rich Exhaust Signal

PFI Chart A-11:

PFI Oxygen Sensor Circuit:

DESCRIPTION:

The PCM/ECM provides a 0.45 volt reference signal to the oxygen sensor on CKT 912. 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 High oxygen sensor voltage readings are 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 engine emission or fuel system.

Less likely is the possibility that the oxygen sensor has failed and is giving an incorrect high reading. However If this is the case, the closed loop fuel system will overcompensate and cause a lean operation while the 02 sensor is indicating rich.

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 lean readings.

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 restricted air cleaner could cause a rich fuel mixture. Inspect the cleaner and replace if necessary.

b. 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. Also check for vacuum not present at fuel pressure regulator. Fuel pressure should vary with engine load.

c. 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.

d. Carbon canister loaded with fuel can cause rich operation, see Chart C-3.

e. Vacuum leak to the MAP sensor can cause a false high MAP reading. High MAP readings cause the PCM/ECM to deliver too much fuel for current driving conditions. See code E034, NOTE ON INTERMITTENTS, to diagnose.

f. Injector dripping or injector leaks can cause rich exhaust. To check injectors, see Chart A-5.