Powertrain Controls - ECM/PCM

DTC 45 Chart:

Oxygen Sensor (O2S) Schematic:

CIRCUIT DESCRIPTION
In order for the Powertrain Control Module (PCM) to maintain the proper air/fuel ratio an Oxygen Sensor (O2S) sensor is used to monitor combustion efficiency. The O2 sensor produces a voltage between 0.1V indicating lean exhaust - high oxygen content to 1.0V (rich exhaust - low oxygen content). When the O2 sensor voltage is low indicating lean exhaust the PCM will compensate by adding fuel (increasing injector pulse width) to maintain proper air/fuel ratio of 14.7 to 1. If the O2 sensor voltage does not decrease when the PCM commands less fuel a DTC will set.

DIAGNOSTIC TROUBLE CODE (DTC) 45 WILL SET WHEN
^ O2S voltage is greater than 0.75 volt.
^ DTC 33 or 34 is not set.
^ O2S system is in "Closed Loop."
^ Throttle Position (TP) sensor angle is between 5% and 93.8%.
OR
^ O2S voltage is above 1 volt for 5 seconds or more.
^ Above conditions are met for 30 seconds or more.

ACTION TAKEN (PCM WILL DEFAULT TO)
The Malfunction Indicator Lamp (MIL) will illuminate, and the cooling fan will enable.

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

1. This step determines if DTC 45 is the result of a hard failure or an intermittent condition.

DIAGNOSTIC AIDS
DTC 45 or rich exhaust is most likely caused by one of the following;

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 will be set. See "Fuel System Diagnosis," CHART A-7. Related Tests, Information and Procedures

Leaking injector
See CHART A-7. Related Tests, Information and Procedures

Exhaust Gas Recirculation (EGR) valve
A stuck open EGR valve will cause the O2 sensor to indicate a rich exhaust condition.

Evaporative Emissions (EVAP) canister purge
Check for fuel saturation. If full of fuel, check canister control and hoses. See Chart C-3. Chart C-3 EVAP Canister Purge Valve Check

Manifold Absolute Pressure (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 MAP sensor if the rich condition is gone while the sensor is disconnected.

Pressure regulator
Check for a leaking fuel pressure regulator diaphragm by checking for liquid fuel in the vacuum line to the regulator.

Throttle Position (TP) sensor
A TP sensor output will cause the system to go rich due to a false indication of the engine accelerating.

O2S contamination
Inspect O2S for silicone contamination from fuel or use of improper RTV sealant. The sensor may have a white powdery coating and result in a high but false signal voltage (rich exhaust indication). The PCM will then reduce the amount of fuel delivered to the engine causing a severe surge driveability problem.