Diagnostic Aids
Using scan tester, observe block learn values at different RPM and airflow conditions to determine when Code 44 may have been set.
If conditions for Code 44 are present, block learn values will be approximately 150.
- Oxygen sensor pigtail may be mispositioned and contacting exhaust manifold.
- Check for intermittent ground in wire between connector and sensor.
- A MAP sensor output causing ECM to sense a higher than normal vacuum will cause system to go lean. Disconnect MAP sensor. If lean condition is gone, replace sensor.
- Water near the in-tank fuel pump inlet can be delivered to the injectors, causing a lean exhaust. This can set a Code 44.
- Fuel system will be lean if pressure is too low. Monitor fuel pressure while driving vehicle at various speeds and/or loads to confirm a problem (if necessary).
- 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, see INTERMITTENTS under TESTS W/O CODES article in the ENGINE PERFORMANCE Section.