Powertrain Controls - ECM/PCM

DTC 45 Diagnostic Chart:

Heated Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volt (450 mV) between terminals "A10" and "A12". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt (320 mV). The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1 volt 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 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 or CKT 412:
^ Remains above 0.70 volt (700 mV) for 70 seconds, and in "Closed Loop."
^ Engine time after start is 1 minute or more.
^ Throttle angle less than 5% (about 0.2 volt above idle voltage).

DIAGNOSTIC AIDS:
Using the TECH 1 scan tool, observe the long term fuel trim values at different RPM and air flow conditions to determine when the DTC 45 may have been set. If the conditions for DTC 45 exist, the long term fuel trim 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 DTC 45 may be set.
Refer to Chart A-6 Fuel System Diagnosis
Related Tests, Information and Procedures
^ LEAKING INJECTOR.
^ Check for fuel contaminated oil.
^ HEATED OXYGEN SENSOR (HO2S) WIRE - An oxygen supply inside the HO2S is necessary for proper HO2S operation. This supply of oxygen is supplied through the HO2S wire. All HO2S wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the HO2S.
^ DI SHIELDING - An open ground CKT 453 (ignition system reference low) may result in 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.
^ CANISTER PURGE - Check for fuel saturation. If full of fuel, check canister control and hoses.
Refer to Emission Control Systems/Evaporative Emissions System/Testing and Inspection/Procedures/Evaporative Emission Control System Testing
Testing and Inspection
^ 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 presence of liquid fuel.
^ TP SENSOR - An intermittent TP signal output will cause the system to go rich, due to a false indication of the engine accelerating.
^ ECT SENSOR - Check for a shifted sensor that could cause a rich exhaust but set a DTC 15.
Refer to Code 15 Engine Coolant Temperature Sensor High
DTC 15