Diagnostic Aids
Using "Scan" tester, observe the block learn values at different RPM and airflow conditions to determine when Code 44 may have been set. If the conditions for Code 44 exist, block learn values will be around 150.
- Oxygen sensor pigtail may be mispositioned and contacting the exhaust manifold.
- Check for intermittent ground in wire between connector and 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. If the lean condition is gone, replace sensor.
- 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 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 a problem.
- If there is an exhaust leak, outside air can be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can also cause a lean condition.
- If the above are okay, problem is a faulty oxygen sensor.
For intermittent inspection procedures, refer to INTERMITTENTS in the TESTS W/O CODES - EFI article.