Powertrain Control Module - PCM

Diagnostic Trouble Code 45:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
This DTC chart applies to heated and non-heated oxygen sensors, The PCM supplies a voltage of about 450 mV between terminals "A10" and "A12." (If measured with a 10 megohm digital voltmeter, this may read as low as 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 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.

DTC 45 WILL SET WHEN
^ Remains above 750 mV for 61-71 seconds, and in "Closed Loop."
^ Engine time after start is 1 minute or more.
^ Throttle angle is greater than 5%.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will enable the MIL.

DTC 45 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech I "clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and battery feed voltage is removed for 10 seconds.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Check operating temperature and HO2S voltage having a high reading.

2. Checks the PCM and refer to "Diagnostic Aids" to check other variables.

DIAGNOSTIC AIDS
Using the Tech 1, observe the block learn 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 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 DTC 45 may be set.
Refer to Fuel Delivery And AIR Induction / Testing And Inspection / Procedures / Fuel Pressure Test.
^ LEAKING INJECTOR.
^ Check for fuel contaminated oil.
^ HO2S SENSOR 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.
^ MAP SENSOR - An output that causes the PCM to sensor 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 chart for Code 15 Coolant Temperature Sensor (CTS) Circuit Powertrain Controls - ECM/PCM