Powertrain Controls - ECM/PCM

DTC 44 Chart:

Left (Bank 2) Oxygen Sensor Circuit:

Circuit Description:
The Powertrain Control Module (PCM) supplies a voltage of about .45 volt between terminals "B21" and "B20." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.)

When the O2S reaches operating temperature, it varies this voltage from about 100 millivolts (exhaust is lean) to about 900 millivolts (exhaust is rich).

The sensor is like an open circuit and produces no voltage when it is below 316°C (600°F). An open sensor circuit, or cold sensor, causes "Open Loop" operation.

DTC 44 Will Set When:
Vehicle is operating in "Closed Loop" and CKT 1665 is below 280 millivolts for greater than 60 seconds.

Action Taken (PCM will default to):
Vehicle will operate in "Open Loop" and MIL will become illuminated.

DTC 44 Will Clear When:
A current DTC 44 will clear when the O2S voltage rises above the calibrated lean exhaust voltage threshold. A history DTC 44 will clear after 50 consecutive ignition key cycles without a current DTC 44 being stored.

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

1. The engine must be operating in "Closed Loop" to store DTC 44.

Diagnostic Aids:
Using the Tech 1 scan tool, observe the long term fuel trim at different RPM and air flow conditions. The Tech 1 scan tool also displays the 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.

- 02S wire. Sensor pigtail may be mispositioned and contacting the exhaust manifold.
- Check for intermittent ground in wire between connector and sensor.
- Lean injector(s). Perform "Injector/Coil Balance Test," CHART C-2A. Testing and Inspection
- 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 02S signal 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 correct fuel pressures. Refer to "Fuel System Diagnosis," CHART A-7. 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.
- If the above are OK, it is a faulty Oxygen Sensor (02S).