Powertrain Controls - ECM/PCM

DTC 45 Diagnostic Chart:

Oxygen Sensor Circuit:

Circuit Description
The PCM supplies a voltage of about .45 volt between terminals "A10" and "A12". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen Sensor (O2S) varies the voltage within a ran e of about 1 volt if the exhaust is rich, down through about .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.

DTC 45 Will Set When
The oxygen sensor signal voltage or CKT 412:
^ Remains above .6 volt for 203 seconds, and in "Closed Loop."
^ Engine time after start is 1 minute or more.
^ Throttle an le less than 10%.

Action Taken (PCM will default to)
The PCM will turn "ON" the MIL (Malfunction Indicator Lamp).

DTC 45 Will Clear When
Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and fuse #9 (ECM B) fuse is removed for 10 seconds.

DTC Chart Test Description
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Check operating temperature and HO2S voltage having a high reading.

2. Checks the PCM and refer to "Diagnostic Aids" to check other variables.

Diagnostic Aids
Using the Tech 1, observe the bloc learn values at different RPM and air flow conditions to determine when the DTC 45 may have been set. If the conditions for DTC 45 exist, the block learn values will be around 115.

^ Fuel pressure - System will go rich if pressure is too high. The PCM can compensate for some increase. However, if it gets too high, a DTC 45 may be set.

Refer to "Fuel System Diagnosis" chart. Related Tests, Information and Procedures

^ Leaking injector.
^ Check or fuel contaminated oil.
^ Heated Oxygen (HO2S) sensor wire - An oxygen supply inside the 02S is necessary for proper O2S operation. This supply of oxygen is supplied through the 025 wire. All O2S wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the 02S.
^ DI shielding - An open ground CKT 453 (ignition system reference low) may result in EMI, or induced electrical "noise." The PCM looks at this "noise" as reference pulses. The additional pulses result in a higher than actual engine speed signal. The PCM 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.
^ MAP sensor - An output that causes the PCM to sensor a higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the PCM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.
^ Pressure regulator - Check for leaking fuel pressure regulator diaphragm by checking for presence of liquid fuel.
^ TP sensor - An intermittent TP signal Output will cause the system to go rich, due to a false indication of the engine accelerating.
^ ECT sensor - Check for a shifted sensor that could cause a rich exhaust but set a DTC 15, refer to chart for DTC 15.