Symptoms

- Engine Light ON (or Service Engine Soon Warning Light) - Improper shifting timing

Possible Causes

- ECM Harness - ECM connectors - Automatic transmission control unit harness - Automatic transmission control unit connector - The circuit between ECM and A/T control unit is open or shorted - Low battery voltage - Faulty automatic transmission control unit - Faulty ECM

When Detected

ECM receives incorrect voltage from A/T control unit continuously

Description

These circuit lines are used to control the smooth shifting up and down of A/T during the and acceleration/deceleration. Voltage signal are exchanged between the Engine Control Module (ECM) and Automatic Transmission (A/T) control unit.