E044

Diagnostic Chart.:

PCM Wiring:

DESCRIPTION:

The PCM/ECM provides a .45 volt reference signal to the oxygen sensor on CKT 412. When the oxygen sensor is cold (below 200°C), the oxygen sensor signal voltage will be around 0.45 volts, and the PCM/ECM will keep the system in open loop operation. When the oxygen sensor is warm (above 200°C), 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.

When the PCM/ECM sees that the oxygen is varying from the cold voltage of 0.45 volt, it will send the system into closed loop operation. In closed loop operation, the PCM/ECM will adjust the fuel delivery rate to the engine based on the oxygen sensor readings. Code E044, is designed so that if the oxygen sensor stays at a lean voltage for more than 45 seconds during the test conditions, code E044 will set.

Code E044 will set when:

1. There is an oxygen sensor circuit fault giving a false lean indication.
2. When the air fuel ratio is actually lean due to a vacuum leak or fuel control system fault.

TEST CONDITIONS:

1. Codes E014, E015, E016, E021, E022, E026, E027, E031, E032 and E034 all MUST be clear.
2. Throttle switch open.
3. TPS between 6 and 30 degrees and steady.
4. Coolant temp 58°C or greater.
5. Oxygen sensor ready (closed loop).
6. Not accelerating or decelerating.
7. Engine speed greater than or equal to 800 RPM.
8. Canister purge has purged at full duty cycle for 10 minutes since the engine was running with coolant 80°C and TPS 10° or greater.

FAILURE CONDITIONS:

Oxygen sensor status stays lean for more than 50 seconds.

ACTION TAKEN:

1. PCM/ECM turns on "SERVICE ENGINE SOON" telltale.
2. PCM/ECM turns on canister purge.

NOTES ON FAULT TREE:

1. With the oxygen sensor disconnected, parameter ED33 should remain at reference voltage (.38 to .63 volts)

2. 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 412 to above .64 volts (rich). Similar results may be obtained by placing one finger on battery positive terminal and another finger on oxygen sensor CKT 412 harness terminal.

3. The PCM/ECM compares oxygen sensor signal voltage received on circuit 412 to the ground voltage on circuit 413. If the PCM/ECM doesn't have a good ground to the engine on circuit 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 the PCM/ECM terminal A1. 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 on CKT 413 between PCM/ECM terminal A1 and the ground at front of engine, right (rearmost) head.

NOTE ON INTERMITTENTS:

Engine running, manipulate the oxygen sensor and PCM/ECM wiring and connectors while observing PCM/ECM data ED33. If the fault is induced, ED33 will jump below .37 volts and the "ECON" status light will go off. Manipulate CKT 413 ground to the engine and look for a loose ground eyelet or ground eyelet installed at wrong location. If lean engine operation is suspected, perform the PFI SYSTEM CHECK under "C" CHARTS. "Excessive Exhaust Emissions" - NOx. An engine that is misfiring may have a lean oxygen sensor indication because of unburned oxygen in the exhaust stream. If the oxygen sensor circuit appears to be OK, go to OXYGEN SENSOR CIRCUIT CHECK under "C" CHARTS, to check for faulty or contaminated sensor.