Engine Control Module ECM

DTC 45:

DTC 44 O2S Circuit:

Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (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 range of about 1 volt if the exhaust is rich, to 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 (O2S) signal voltage or CKT 412:

^ Remains above .7 volt for 60 seconds, while in "Closed Loop."

^ Engine time after start is one minute or more.

^ Throttle angle greater than 5% (about .2 volt above idle voltage).

Action Taken (ECM will default to): The Malfunction Indicator Lamp (MIL) will illuminate.

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 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. Checks to see if DTC was set as result of a hard failure or intermittent condition. Also checks wiring and ECM.

Diagnostic Aids: Using the Tech 1 scan tool, observe the long term fuel trim 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 long term fuel trim values will be around 115. The MIL will remain "ON" until the ignition is turned "OFF," due to possible high fuel pressure.

An oxygen supply inside the O2S is necessary for proper O2S operation. This supply of oxygen is routed through the O2S wires. All O2S wires and connections should be inspected for breaks or contamination which could prevent reference oxygen from reaching the O2S.

^ 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 DTC 45 may be set.
Refer to A CHARTS/ CHART A-6 FUEL SYSTEM DIAGNOSIS Related Tests, Information and Procedures.

^ Check for fuel contaminated oil. Refer to "Fuel System Diagnosis" chart.

^ DI SHIELDING - An open ground CKT 453 (ignition system reference low) 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.

^ MAP SENSOR - An output which causes the ECM to read higher than normal manifold pressure (low vacuum) can cause the system to go rich. Disconnecting the MAP sensor will allow the ECM to set a fixed value for the MAP sensor. Substitute a different MAP sensor if the rich condition is gone.

^ PRESSURE REGULATOR - Check for leaking fuel pressure regulator diaphragm by checking for presence of liquid fuel.

^ TP SIGNAL - An intermittent TP signal output will cause the system to go rich, due to a false indication of the engine accelerating.

^ ECT - Check for a skewed sensor which could cause a rich exhaust and set a DTC 15. Refer to chart for CODE 15 COOLANT TEMPERATURE SENSOR (CTS) CIRCUIT" Powertrain Controls - ECM/PCM.