Powertrain Controls - ECM/PCM

DTC 44 Chart:

Heated Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The PCM provides a 0.45 volt reference signal to the HO2S on CKT 412. When the HO2S is cold, below 200°C (392°F), the HO2S signal voltage will be around 0.45 volt and the PCM will keep the system in "Open Loop" operation. When the HO2S is warm, above 200°C (392°F), the HO2S will swing from rich to lean rapidly, at least one swing every two seconds, if the PCM is in good control of the air fuel mixture, DTC 44 is designed so that the HO2S stays at a lean voltage for more than 50.3 seconds during the test conditions, DTC 44 will set.

DTC 44 WILL SET WHEN
- DTCs 14, 15, 16, 21, 22, 26, 27, 31, 32, 34 and 119 are not set.
- HO2S remains lean (356 mV) or less for more than 50 seconds.
- Throttle switch open.
- TP angle between 5.4° and 25°.
- Coolant temperature above 82.5°C.
- HO2Sready.
- Engine speed 800 RPM or greater.
- Low coolant level and engine overheat not present.
- Traction control not active.
- MAP greater than 20.2 kPa.

DTC 44 WILL CLEAR WHEN
The fault no longer exists and ignition is cycled "OFF" and "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If DTC 13 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.
2. If the oxygen sensor is operating correctly, voltage will fluctuate above 0.3 volt. A lean sensor/condition will cause the voltage to remain below 0.3 volt.
3. If greater than 0.15 volt is measured, the PCM and CKT 412 are OK.

DIAGNOSTIC AIDS
Using the Tech 1 tool 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 conditions for DTC 44 exist the long term fuel trim values will be around 150.

HO2S 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 Balance Test," Chart C-2A. Chart C-2A Injector Coil Balance Test Procedure

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 HO2S 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 car at various road speeds and/or loads to confirm. Refer to "Fuel System Diagnosis," Chart A-7. Chart A-7 Fuel System Pressure Test

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 Heated Oxygen Sensor (HO2S).