Powertrain Controls - ECM/PCM

DTC 45 Oxygen Sensor Circuit (Rich Exhaust):

Oxygen Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volt between terminals "D6" and "D7." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The Oxygen Sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.01 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.

DIAGNOSTIC TROUBLE CODE (DTC) 45 WILL SET WHEN
System is operating in "Closed Loop," O2S signal voltage is greater than 0.700 volt for 50 seconds, Throttle Position (TP) angle is between 0% and 99.6%.

ACTION TAKEN (PCM WILL DEFAULT TO)
Vehicle will operate in "Open Loop" and Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 45 WILL CLEAR WHEN
A current DTC 45 will clear when the O2S signal voltage falls below the calibrated rich exhaust voltage threshold. A history DTC 45 will clear after 50 consecutive ignition key cycles without a current DTC 45 being stored.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The engine must be operating in "Closed Loop" to store DTC 45.

DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the Long Term (L.T.) fuel trim values at different RPM conditions to determine when the DTC 45 may have been set. If the conditions for DTC 45 exist, the L.T. fuel trim values will be around 90.
^ 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 A Charts/Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures
^ Leaking injector - Refer to A Charts/Chart A-7 Fuel System Diagnosis.
^ Check for fuel contaminated oil.
^ Ignition shielding - An open ground CKT 453 (ignition system reference low) may result in Electro Magnetic Interference (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.
^ Evaporative canister purge - Check for fuel saturation. If full of fuel, check canister control and hoses. See Emission Control Systems/Evaporative Emissions System.
^ Manifold Absolute Pressure Sensor - A (MAP) output that causes the PCM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the MAP sensor will allow the PCM to set a fixed value for the sensor. Substitute a different MAP sensor if the the rich condition is gone while the sensor is disconnected.
^ TP Sensor - An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.