Powertrain Controls - ECM/PCM

DTC 44 Diagnostic Chart:

Heated Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volt between terminals "A10" and "A12". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt) The Heated Oxygen Sensor (HO2S) varies the voltage within a range of near 1 volt if the exhaust is rich, down through about 0.1 volt if exhaust is lean.

CHART TEST DESCRIPTION:
Numbers below refer to circled numbers on the diagnostic chart.
1. DTC 44 is set when the Oxygen Sensor (O2S) signal voltage on CKT 412:
^ Remains below 0.1 volt (100 mV) for 70 seconds.
^ Maximum air fuel ratio is 14.6.
^ And the system is operating in "Closed Loop."

DIAGNOSTIC AIDS:
Using the TECH 1 scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The TECH 1 scan tool 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.
^ OXYGEN SENSOR (O2S) WIRE - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ HEATED OXYGEN SENSOR (HO2S) 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 Chart A-6 Fuel System Diagnosis
Related Tests, Information and Procedures
^ 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 0.45 volt. This may also cause DTC 13 to set.
^ If all check OK, the O2S is faulty.