Powertrain Controls - ECM/PCM

DTC 45 - Oxygen Sensor Circuit (Rich Exhaust Indicated):

Oxygen Sensor Wiring Circuit:

Circuit Description:
The Powertrain Control Module (PCM) supplies a voltage of about .45 volt between terminals "PA12" and "PB6". (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, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor will cause "Open Loop" operation.

DTC 45 Will Set When:
^ O2S voltage is greater than .75 volt.
^ DTC 33 or 34 is not set.
^ Fuel system is in "Closed Loop."
^ TP sensor is between 5% and 93.8%.
^ Above conditions are met for 5 seconds or more.
OR
^ O2S voltage is above 1 volt. for 5 seconds or more.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate, and the cooling fan will enable.

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

1. This step determines if DTC 45 is the result of a hard failure or an intermittent condition.

Diagnostic Aids: DTC 45 or rich exhaust is most likely caused by one of the following:

^ 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 will set. See "Fuel System Diagnosis," CHART A-7. Related Tests, Information and Procedures
^ Leaking injector - See CHART A-7. Related Tests, Information and Procedures
^ Electronic Ignition (El) shielding - An open ground CKT 574 may result in EMI or induced electrical noise. The PCM looks at this noise as Crankshaft Position (CKP) sensor 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.
^ EVAP canister purge - Check for fuel saturation. If full of fuel, check canister control and hoses. See "Evaporative Emission (EVAP) Control System." Evaporative Emissions System
^ MAP sensor - An output that causes the PCM to sense 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 the presence of liquid fuel in the vacuum line to the regulator.
^ TP sensor An intermittent TP sensor output will cause the system to go rich due to a false indication of the engine accelerating.
^ O2S contamination - Inspect O2S for silicone contamination from fuel or use of improper RTV sealant. The sensor may have a white powdery coating and result in a high but false signal voltage (rich exhaust indication). The PM will then reduce the amount of fuel delivered to the engine causing a severe surge driveability problem.