Powertrain Controls - ECM/PCM

Oxygen Sensor Circuit Diagram:

CIRCUIT DESCRIPTION:
The PCM supplies a voltage of about 0.45 volt (450 mV) between terminals "BD3" and "BD2". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The 02 sensor varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich, down through about 0.10 volt (100 mV) if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 316°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Code 45 is set when the following conditions exist:

^ 02 sensor signal voltage or CKT 412 remains above 0.75 volt for 2 minutes while operating in "Closed Loop"
^ Throttle position signal between 0.6 and 1.9 volts (indicating partial load condition - throttle angle between 6% & 40%.)

TEST DESCRIPTION

Code 45 Diagnostic Chart:

Numbers below refer to circled numbers on the diagnostic chart.

1. Determines if the PCM is reading conditions necessary to set a code 45.

DIAGNOSTIC AIDS:

Using the "Scan," observe the block learn values at different rpm 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 115.

^ 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 Code 45 may be set.Related Tests, Information and Procedures
^ Rich Injector - Perform injector balance test. Chart C-2A Fuel Injector Balance Test
^ Leaking Injectors - Related Tests, Information and Procedures
^ Check for fuel contaminated oil.
^ Canister Purge - Check for fuel saturation. If full of fuel, check canister control and hoses.
^ MAF Sensor - An output that causes the PCM to sense a higher than normal airflow can cause the system to go rich. Disconnecting the MAF sensor will allow the PCM to set a fixed value for the sensor. Substitute a different MAF sensor if the rich condition is gone while the sensor is disconnected.
^ Check for leaking fuel pressure regulator diaphragm by checking vacuum line to regulator for fuel.
^ TPS - An intermittent TPS output will cause the system to go rich due to a false indication of the engine accelerating.