Powertrain Controls - ECM/PCM

DTC 44 Chart:

Oxygen Sensor (O2S) Schematic:

CIRCUIT DESCRIPTION
In order for the Powertrain Control Module (PCM) to maintain the proper air/fuel ratio an Oxygen (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 increase when the PCM commands more fuel a DTC will set.

DIAGNOSTIC TROUBLE CODE (DTC) 44 WILL SET WHEN
^ DTC 33 or 34 is not set.
^ The system is operating in "Closed Loop."
^ O2S signal voltage remains less then 0.3 volt for 50 seconds or more.
^ Throttle Position (TP) sensor angle 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
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.

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 Manifold Absolute Pressure (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.

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

Engine misfire
A cylinder misfire will result in oxygen in the exhaust. Refer to CHART C4-M and / or Diagnosis by Symptom. Chart C-4M Electronic Ignition System Misfire Diagnosis

Cracked Oxygen Sensor
Refer to Diagnosis by Symptom. Testing and Inspection

Plugged fuel filter
A plugged fuel filter can cause a lean condition.

Plugged Oxygen Sensor
A plugged reference port on the Oxygen Sensor will indicate a lower than normal voltage output.

Other Possible Causes
- A short to ground in oxygen sensor CKT 412.
- Exhaust leak.
- Vacuum leak.
- Crankcase leak.