Computer Relearn Procedures: Introduction

Vehicles equipped with engine or transmission computers may require a relearn procedure after the vehicle battery is disconnected. Vehicle computers memorize and store vehicle operation patterns for optimum driveability and performance. When the vehicle battery is disconnected, this memory is lost. Default data is used until new data from each key start is stored. As the computer restores its memory from each new key start, driveability is restored.

Driveability problems may occur during the relearn stage. Depending on the vehicle and how it is equipped, the following driveability problems may exist:

• Rough or unstable idle.
• Hesitation or stumble.
• Rich or lean running.
• Poor fuel mileage.
• Harsh or poor transmission shift quality.

To accelerate relearn process after battery removal and installation, vehicle should be road tested in the following manner:

• Vehicle at normal operating temperature (cooling fan cycles).
• Accelerate at normal throttle position (20-50%).
• Cruise at light to medium throttle.
• Decelerate to a stop, downshifting and using brakes normally.

Manufacturers identify specific relearn procedures. See RELEARN PROCEDURES. Always complete the procedure before returning the vehicle to the owner.