Diagnostic Aids

Using Scan tester, observe block learn value at different RPM. Scan tester also displays block cells, so block learn values can be checked in each of the cells, to determine when Code 44 set. If conditions for Code 44 exist, block learn values will be approximately 150.

• Ensure oxygen sensor pigtail is not contacting exhaust manifold.
• Check for ground in wire between connector and oxygen sensor.
• Water delivered to fuel injectors can cause a lean mixture. This can set a Code 44.
• Fuel system will be lean if pressure is too low. Monitor fuel pressure while driving at various road speeds and/or loads to confirm a problem (if necessary).
• If exhaust leak is present, outside air can be pulled into the exhaust and past the sensor. Vacuum or crankcase leaks can also cause a lean condition.
• If heater portion of oxygen sensor fails, this may set a Code 44 or 45. See SYSTEM/COMPONENT TESTS - EFI article.

For intermittent inspection procedures, refer to INTERMITTENTS in the H - TESTING W/O CODE - EFI article.

Fig 1: Code 44: O2 Sensor Lean Mix (Heated Only) Circuit Diagram

Courtesy of ISUZU MOTOR CO.

Fig 2: Code 44: O2 Sensor Lean Mix (Heated Only) Flow Chart

Courtesy of ISUZU MOTOR CO.