DTC 44

Diagnostic Chart





Circuit Diagram

Circuit Description
The engine control module supplies a voltage of about 0.43 volts between terminals "B3" and "B2". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The heated oxygen sensor varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about 0.10 volts, if exhaust is lean. The sensor is like an open circuit and produces no voltage, when it is below about 360°C (600°F). An open sensor circuit, or cold sensor, cause "Open Loop" operation.

Test Description
The number(s) below refer to the circled number(s) on the diagnostic chart.
1. Diagnostic trouble code 44 is set, when the heated oxygen sensor signal voltage is fixed below 0.100 mV and the following:
- Throttle position sensor greater than 9.8%.
- No diagnostic trouble code 21 or 33.
- The engine has been running at least for 180 seconds.
- System is operating in "Closed Loop".
- Oxygen signal voltage is steady between 0.347 volt and 0.547 volts.
- Engine operation temperature is 69.5°C (155°F).
- All of the above conditions present for 25 seconds.
- Integrator not at 128.

Diagnostic Aids
Using the "Scan Tool", observe the block learn value at different revolutions per minute. The "Scan Tool" also displays the block cells, so the block learn values can be checked in each of the cells, to determine when the diagnostic trouble code 44 may have been set. If the conditions for diagnostic trouble code 44 exist, the block learn values will be around 15O.
- Check for ground in wire between connector sensor.
- Fuel contamination: Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean heated oxygen sensor signal and can set a diagnostic trouble code 44.
- Fuel pressure: System will be lean if pressure is too low. If may be necessary to monitor fuel pressure, while driving the car at various road speeds and/or loads to confirm.
- 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.
- Fuel injectors: The wrong fuel injector(s) could be the cause of a lean heated oxygen sensor signal condition. Verify that the correct fuel injector(s) are installed in the vehicle. Refer to the service parts manual for correct part and part number.