Powertrain Controls - ECM/PCM

DTC 45 Chart:

Oxygen Sensor Circuit:

*** Procedure Modified per TSB #41-65-28 **

CIRCUIT DESCRIPTION
This Diagnostic Trouble Code (DTC) chart applies to heated and non-heated oxygen sensors. The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between terminals "A10" and "A12". (If measured with a 10 mega-ohm digital voltmeter, this may read as low as 320 mV.) The Oxygen Sensor (O2S) 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 to 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 Malfunction Indicator Lamp (MIL).

DTC 45 WILL CLEAR WHEN
Conditions for fault are no longer present and Tech 1 scan tool "clear DTCs" function is used, 50 ignition switch keycycles have passed with no further faults, or ignition switch is turned "OFF" and ECM "B" fuse 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 scan tool, 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 A-Charts / Chart A-6 Fuel System Diagnosis. Related Tests, Information and Procedures

Leaking Injector

Contaminated Fuel
Check fuel for contaminated oil.

Heated Oxygen (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.

Distributor 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.

Manifold Absolute Pressure (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.

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

Engine Coolant Sensor (ECT)
Check for a shifted sensor that could cause a rich exhaust but set a DTC 15, refer to Diagnostic Trouble Code Charts / DTC 15 Coolant Sensor Circuit. DTC 15