Powertrain Controls - ECM/PCM

DTC 44 Chart:

Oxygen Sensor (O2S) Circuit:

CIRCUIT DESCRIPTION
In order for the Powertrain Control module (PCM) to maintain the proper air/fuel ratio an Oxygen Sensor (O2S) is used to monitor combustion efficiency. The O2S produces a voltage between 0.1V (indicating lean exhaust - high oxygen content) to 1v (rich exhaust - low oxygen content). When the O2S 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 O2S voltage does not increase when the PCM commands more fuel a DTC will set.

DTC 44 WILL SET WHEN
- O2S signal voltage remains less then 0.3 volt for 50 seconds or more.
- The system is operating in "Closed Loop."
- DTC 33 or 34 is not set.
- The Throttle Position (TP) sensor is between 5% and 93.8%.

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 44 is the result of a hard failure or an intermittent condition.

DIAGNOSTIC AIDS
- DTC 44 or lean exhaust is most likely caused by one of the following:

Fuel Pressure
System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

Manifold Absolute Pressure (MAP) sensor
An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (default) value for the MAP sensor. If the rich condition is gone when the sensor is disconnected, substitute a known good sensor and recheck.

Fuel contamination
Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set a DTC 44.

Sensor harness
Sensor pigtail may be mispositioned and contacting the exhaust manifold.

Engine misfire
A cylinder misfire will result in unburned oxygen in the exhaust, which could cause DTC 44. Refer to Chart C-4M Electronic Ignition System Misfire Diagnosis. Chart C-4M Electronic Ignition System Misfire Diagnosis

Cracked O2S
A cracked 02S or poor ground at the sensor, could cause DTC 44.

- Plugged fuel filter.
- Plugged O2S.
- Exhaust leak.
- Vacuum leak.
- Crankcase leak.