NOTE: Some models are equipped with 2 oxygen sensors. On these models, Code 44 will set if the left sensor circuit is lean. Code 64 will set if the right sensor circuit is lean. Use this chart for Code 64 also and perform tests for applicable sensor.

O2 sensor acts like an open sensor circuit and produces no voltage when exhaust temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation. On models with 2 oxygen sensors, Code 44 will reflect a lean left O2 sensor; Code 64 will indicate a lean right O2 sensor. Perform test procedures for right or left sensor as necessary.

Code is set when O2 sensor voltage signal at control module is low (less than 0.3 volt) for a precalibrated period and fuel system is operating in "closed loop" and attempting to richen mixture. Most likely causes for setting of code are: an actual lean condition, a short to ground on sensor signal circuit or a faulty PCM.

NOTE: Test number refers to number on diagnostic chart.

Checks to see if O2 sensor is registering a lean condition.

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

Code 44: Lean Exhaust Indication: Notes

Use the Manual With the Right Hardware

When to See a Mechanic

Rather have a pro handle this?