Using Scan tester, observe block learn values at different RPM. Scan tester also reads block cells, so block learn values can be checked in each of the cells 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.
An 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 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). Verify correct fuel injectors are installed in vehicle.
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 in TESTS W/O CODES article in the ENGINE PERFORMANCE Section.

Fig 1: Code 44 Schematic - O2 Sensor (Lean Fuel Mixture)

Courtesy of ISUZU MOTOR CO.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Diagnostic Aids

Use the Manual With the Right Hardware

When to See a Mechanic

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