Powertrain Controls - ECM/PCM

DTC 44 (PCM):

O2S Circuit (PCM):

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 Oxygen Sensor (02S) varies the voltage within a range of about 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 about 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 44 is set when the Oxygen Sensor (02S) signal (02S) voltage on CKT 412:
- Remains below 0.1 volt from 70 seconds.
- The system is operating in "Closed Loop."
- Maximum air fuel ratio 14.6.

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 exists, the block learn 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 02S is necessary for proper O2S operation. This supply of oxygen is supplied through the 02S wire. All 02S wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the 02S.

- 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.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,

- 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 (O2S) is faulty.