Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 45:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "C13" and "C14." (If measured with a 10 megohm digital voltmeter, this may display as low as 0.32 volt). The Oxygen Sensor (O2S) voltage reads about 1 volt if a rich 02S signal is indicated, down through about 0.10 volt if a lean O2S signal is indicated.

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. DTC 45 is set when the Oxygen Sensor signal voltage on CKT 412.

^ Remains above 0.75 volt for 30 seconds; and in "Closed Loop."
^ Throttle angle greater than 20% (about 0.2 volt above idle voltage) or less than 2%.

DIAGNOSTIC AIDS
Using the scan tool observe the long term fuel trim values at different RPM conditions to determine when the Diagnostic Trouble Code (DTC) 45 may have been set. If the conditions for DTC 45 exists, the long term fuel trim 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 DTC 45 may be set. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Leaking Injector. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Check for fuel contaminated oil.

^ Ignition Shielding - An open ground CKT 453 (distributor ground, reference low) may result in Electromagnetic Interference (EMI), or induced electrical "noise." The ECM looks at this "noise" as reference pulses.

^ EVAP Canister Purge - Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Chart C-3 EVAP Purge Solenoid Valve Check. Chart C-3 EVAP Canister Purge Valve Check

^ MAP Sensor - An output that causes the ECM to sense a lower than normal vacuum can cause the system to go rich. Disconnecting the Manifold Absolute Pressure (MAP) sensor will allow the ECM to set a fixed value for the sensor. Substitute a different MAP sensor if the rich condition is gone while the sensor is disconnected.

^ Throttle Position (TP) Sensor - An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.