Powertrain Controls - ECM/PCM

DTC 44 Lean Exhaust:

Heated Oxygen Sensor (HO2S) Schematic:

CIRCUIT DESCRIPTION
The 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 0.10 volt if exhaust is lean.

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 SET WHEN
When the Heated Oxygen Sensor (HO2S) signal voltage on CKT 412:
^ Remains below 300 mV for 100 seconds.
^ Maximum air fuel ratio 14.6.
^ And the system is operating in "Closed Loop."

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will turn "ON" the MIL (Malfunction Indicator Lamp).

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 fuse #9 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 HO2S 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.
^ Oxygen Sensor (O2S) wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ 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 H02S.
^ 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.
^ AIR system - Be sure air is not being directed to the exhaust ports while in "Closed Loop." If the block learn value goes down while squeezing air hose to left side of exhaust ports, refer to Air Injection. Emission Control Systems
^ 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 Oxygen Sensor (HO2S) is faulty.