Powertrain Control Module PCM

DTC 44 Chart:

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 Oxygen Sensor (O2S) varies the voltage within a range of near 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.

DTC 44 Will Set When:
PART 1: The Oxygen Sensor (O2S) signal voltage on CKT 412:

^ Remains below 100 mV for 70 seconds.

^ And the system is operating in "Closed Loop."

PART 2:

^ "Open Loop" for 10 seconds.

^ Maximum air fuel ratio is 14.6.

Action Taken (PCM will default to): The PCM will enable the MIL. The sensor is like an open circuit and produces no voltage when it is below 315° C (600° F). An open sensor circuit or cold sensor causes "Open Loop" operation.

DTC 44 Will Clear When: Conditions for fault are no longer present and Tech 1 "clear DTCs" function is used or 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. Checks engine operating temperature and O2S voltage having a low reading.

2. Checks the wiring and PCM first and then to the "Diagnostic Aids" to check other variables and finally the sensor.

Diagnostic Aids: Using the Tech 1, observe the long term fuel trim values at different RPM and air flow conditions. The Tech 1 also displays the long term fuel trim cells, so the long term fuel trim values can be checked in each of the cells to determine when the DTC 44 may have been set. If the conditions for DTC 44 exist, the long term fuel trim values will be around 150.

^ 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.

^ Check for intermittent ground in wire between connector and sensor.

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

^ 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 FUEL DELIVERY AND AIR INDUCTION/ TESTING AND INSPECTION/ PROCEDURES/FUEL PRESSURE TEST. Testing and Inspection

^ EXHAUST LEAKS - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.

^ CKT 413 - If CKT 413 is open, the voltage at terminal "C14" will be about .45 volt. This may also cause DTC 13 to set.

^ If all check OK, the Heated Oxygen Sensor (HO2S) is faulty.