Code 44 - Oxygen Sensor Circuit

(Lean exhaust indicated)

Circuit Description

The ECM supplies a voltage of about 0.45 volt to CKT 412. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The O2 sensor 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 360 C (600 F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Problem Description:

Code 44 is set when the O2 sensor signal voltage or CKT 412:

• Remains below 0.2 volt for 20 seconds

• And the system is operating in "Closed Loop".

Diagnostic Aids:

Using the scantool, observe the block learn values at different RPM and air flow conditions to determine when the Code 44 may have been set. If the conditions for Code 44 exist the block learn values will be around 150.

Check:

• O2 Sensor wire. Sensor pigtail may be mispositioned and contacting the exhaust manifold.

• For intermittent ground in wire between connector and sensor.

• MAP Sensor. A MAP Sensor output that causes the ECM to sense a higher than normal vacuum will cause the system to go lean. Disconnect the MAP sensor and if the lean condition is gone, replace the sensor.

• For lean injector(s). Perform injector balance test CHART C-2A

• For 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 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. See Service Manual Fuel System Diagnosis CHART A-7.

• 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.

• EGR. In normal operation the ECM delivers less fuel and advances spark when EGR comes in. If the EGR does not open, the system will go lean and may have a slight spark knock.

"Scan" Diagnostics:

Run warm engine (75 C to 95 C) at 1200 rpm. Does scantool indicate O2 voltage fixed below 0.35 volts (350mV)?

YES NO