DTC 44

Oxygen Sensor Circuit:

DTC 44 Oxygen Sensor Circuit - Lean Exhaust Indicated:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volt between terminals "D6" and "D7" of the ECM (If measured with a 10 Meg ohm digital voltmeter, this may read as low as 0.32 volt.) The O2 sensor varies the voltage within a range of about 1 volt, if the exhaust is rich, down to about 0.10 volt, if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F). An open sensor circuit, or cold sensor, causes "OPEN LOOP" operation.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 44 will set when the sensor voltage is fixed below .5 (50 mV) and the following occurs:

^ TPS is above 3.5% and less than 13.3% at less than 3000 rpm.
^ No Code 21 or Code 22.
^ System is in "CLOSED LOOP."
^ Coolant temperature above 70° C.
^ Integrator not at 128.

DIAGNOSTIC AIDS:

Using the Scan tool, observe the block learn value at different rpms. The Scan also displays the block cells, so the block learn values can be checked in each of the cells, to determine when the Code 44 may have been set. If the conditions for Code 44 exists, the block learn values will be around 150.

^ 02 Sensor Wire - Sensor pigtail may be mis-positioned and contacting the exhaust manifold. Check for 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 injector. The water causes a lean exhaust and can set a Code 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.
^ Exhaust Leaks - If there is an exhaust leak, outside air can be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can cause a lean condition.
^ If Code 44 is intermittent,
Intermittant Check Procedure