DTC 44

Oxygen Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The PCM applies a voltage of about 0.55 volt between circuits 412 and 413 (if measured with a 10 megohm digital voltmeter, this may read as low as 0.35 volt). The oxygen sensor varies this voltage within the range of 0.1 - 0.9 volt, depending on the oxygen content of the exhaust. The sensor is like an open circuit when cold (below approx. 315°C/600°F). An open sensor circuit or cold sensor causes the system to operate in "OPEN LOOP".

Code 44 will set when:
^ System is operating in closed loop.
^ Voltage in circuit 412 remains below 0.2 volt for 1 minute of more.
^ Codes 33 and 34 not present.
TEST DESCRIPTION

Code 44 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.
1. After running engine as described, system should be in "CLOSED LOOP" and oxygen sensor signal should be varying between 0.3 and 0.6 volt (300 - 600 millivolts.)

DIAGNOSTIC AIDS
Using a "SCAN" tool, check the "Block Learn" values at different engine speeds and air flow conditions.
"SCAN" tool that reads "Block Cells" should be used. "Block Learn" values for each cell can be checked to help determine when the Code 44 may have been set. If conditions for Code 44 exist, "Block Learn" values will be around 150.

Also check the following:

^ Oxygen Sensor Wire Pigtail - Make sure wires are not touching hot exhaust manifold or grounded against sharp metal edges. Check for intermittent ground in wire between sensor and connector.

^ Injectors - Plugged or restricted may cause lean condition in one or more cylinders. If one cylinder is too lean or not firing, the oxygen in the exhaust from that one cylinder may cause a lean exhaust indication. This may cause the system to go to full rich and set a Code 44, as the computer tries to compensate for the one bad cylinder. Perform injector ballance test. Chart C-2A Fuel Injector Balance Test

^ Fuel Pressure - System will be lean if fuel pressure is too low. It may be necessary to monitor fuel pressure while driving vehicle at different speeds and loads to confirm low pressure. Related Tests, Information and Procedures

^ Exhaust leaks - An exhaust leak can draw outside air into the exhaust and past the sensor under certain conditions, causing a false lean indication. Vacuum or crankcase leaks can also cause a lean indication.

^ If all checks out OK, replace oxygen sensor.