Powertrain Controls - ECM/PCM

Oxygen Sensor Circuit Code 44:

Oxygen Sensor Circuit:

Circuit Description:
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen (02) sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 44 is set when the Oxygen (02) sensor signal voltage on CKT 412:
^ Remains below .2 volt from 60 seconds to 4 minutes.
^ And the system is operating in "Closed Loop."

Diagnostic Aids:
Using the Tech 1, observe the block learn values at different rpm and air flow conditions. The Tech 1 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.

^ Oxygen (09) Sensor Wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.

^ Heated 02 Sensor Wire - An oxygen supply inside the 02 sensor operation. This supply of oxygen is supplied through the 02 sensor wires. All 02 sensor wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the 02 sensor.

^ Lean Injector Poppet Nozzles - Perform "poppet nozzle diagnosis" in "Computer Command Control," on 4.3L CPI engine.

^ Check for intermittent 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 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 vehicle at various road speeds and/or loads to confirm. Related Tests, Information and Procedures

^ 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.

^ AIR System - Be sure air is not being directed to the exhaust ports while in "Closed Loop." If the block learn value goes down while squeezing air hose to left side of exhaust ports, see Air Management Check. Initial Inspection and Diagnostic Overview

^ CKT 413 - If CKT 413 is open, the voltage at terminal "D7" will be about .45 volt. This may also cause Code 13 to set.

^ If all check OK, the Oxygen (02) sensor is faulty.