Without Speed Density Update

Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION:
The Electronic Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "E14" and "E15." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F ). An open sensor circuit or cold sensor causes "Open Loop" operation.

TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart.
1. Code 45 is set when the O2 sensor signal voltage on CKT 412.
- Remains above 0.7 volt for 30 seconds; and in "Closed Loop."
- Engine time after start is 1 minute or more.
- Throttle angle between 3% and 45%.

Diagnostic Aids:
Using the "Scan," observe the block learn values at different rpm and air flow conditions. The "Scan" also displays the block cells, so the block learn values can be checked in each of the cells to determine when the Code 45 may have been set. If the conditions for Code 45 exists, the block learn values will be around 115.

Check for short to voltage on CKT 412.

Fuel Pressure. System will go rich if pressure is too high. The ECM can compensate for some increase. However, if it gets too high, a Code 45 may be set. See "Fuel System Diagnosis," CHART A-7. Chart A-7 Fuel System Diagnosis

Rich injector. Perform injector balance test Chart C-2A. Chart C-2A Injector Balance Test

Leaking injector. See CHART A-7. Chart A-7 Fuel System Diagnosis

Check for fuel contaminated oil.

High Energy Ignition (HEI) Shielding. An open ground CKT 453 (ignition system low reference signal) may result in Electro Magnetic Interference (EMI), or induced electrical "noise." The ECM looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The ECM then delivers too much fuel, causing system to go rich. Engine tachometer will also show higher than actual engine speed, which can help in diagnosing this problem.

Canister purge. Check for fuel saturation. If full of fuel, check canister control and hoses. See Chart C-3. Chart C-3 Canister Purge Check

Mass Air Flow (MAF) Sensor. An output that causes the ECM to sense a higher than normal airflow can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAF sensor if the the rich condition is gone while the sensor is disconnected or use tool J-36101 and test MAF Sensor.

Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

Throttle Position Sensor (TPS). An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.

Exhaust Gas Recirculation (EGR). An EGR staying open (especially at idle) will cause the O2 Sensor to indicate a rich exhaust, and this could result in a Code 45.