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With Speed Density Update

O2 Sensor Diagnosis Chart, Rich Indicated:




Wiring Diagram:





CIRCUIT DESCRIPTION:
The Engine 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 Oxygen Sensor (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 315°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 or CKT412:

- 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 value 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.

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, see 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.
- Check for short to voltage on CKT 412.
- Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.

High Energy Ignition (HEI) Shielding
An open ground CKT 453 (ignition system reflow) may result in 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 Canister Purge Valve Check, Chart C-3. Chart C-3 Canister Purge Check

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)
EGR Valve staying open (especially at idle) will cause the O2 sensor to indicate a rich exhaust.