Computer Relearn Procedures: Introduction

Vehicles equipped with engine or transmission computers may require a relearn procedure after the vehicle battery is disconnected. Many vehicle computers memorize and store vehicle operation patterns for optimum driveability and performance. When the vehicle battery is disconnected, this memory is lost. The computer will use default data until new data from each key start is stored. As the computer memorizes vehicle operation for each new key start, driveability is restored. Vehicle computers may memorize vehicles operation patterns for 40 or more key starts.

Customers often complain of driveability problems during the relearn stage because the vehicle acts differently then before being serviced. Depending on the type and make of vehicle and how it is equipped, the following complaints (driveability problems) may exist:

• Harsh Or Poor Shift Quality
• Rough Or Unstable Idle
• Hesitation Or Stumble
• Rich Or Lean Running
• Poor Fuel Mileage

These symptoms and complaints should disappear after a number of drive cycles have been memorized. To reduce the possibility of complaints, after any service which requires battery power to be disconnected, vehicle should be road tested. These procedures are especially important if the vehicle is equipped with an electronically controlled automatic transmission or transaxle. Always complete the procedure before returning the vehicle to the customer.