Powertrain Controls - ECM/PCM

Code 45 Chart:

Wiring Diagram For Oxygen Sensor:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volts between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts). The oxygen sensor varies the voltage within a range of about 1.0 volt if the exhaust is rich, down through about 0.10 volts if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 315°C (680°F). An open sensor circuit or cold sensor causes "Open Loop" operation.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. A Code 45 is set when the oxygen sensor signal voltage on circuit 412:
^ Remains above 0.7 volts for 50 seconds, system in "Closed Loop," engine run time is longer than one minute, and throttle angle is between 2-20%.

DIAGNOSTIC AIDS:

Using the "Scan", observe the block learn values at different engine speeds and air flow conditions "Scan" also displays the block cells, so the block learn values can be checked in each of the cells to determine when the Code 45 may have been set. If the conditions for Code 45 exists, the block learn values will be around 110.

^ 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 Code 45 may be set. Related Tests, Information and Procedures
^ Leaking Injector - See Related Tests, Information and Procedures
^ HEI Shielding - An open ground circuit 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. Chart C-3 Canister Purge Check
^ MAP Sensor - An output that causes the ECM to sense a 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 while the sensor is disconnected.
^ TPS - An intermittent TPS output will cause the system to go rich, due to a false indication of the engine accelerating.
^ CTS - A coolant temperature sensor that indicates a temperature much less than the actual temperature will command a rich mixture from the ECM.
^ Check for fuel contaminated oil.