Circuit Description

WARNING: This page is about a different car, the 2002 Toyota Avalon. However, it is still accessible from the selected car via links, so may be relevant.

CAUTION: If Engine Control Module (ECM) replacement is instructed in following test, always ensure ECM electrical connectors and ground circuits are okay. If either are defective, repair and repeat testing to confirm ECM malfunction. On models equipped with engine immobilizer, if ECM is replaced, ECM must be programmed with proper ignition key code for engine immobilizer system. For programming procedures, see COMPUTER RELEARN PROCEDURES article in GENERAL INFORMATION, or appropriate ENGINE IMMOBILIZER SYSTEMS article in ACCESSORIES & EQUIPMENT.

Wheel speed sensors on each wheel deliver an input signal to Anti-Lock Brake System (ABS) Electronic Control Unit (ECU). ABS ECU converts input signals from wheel speed sensors to a 4-pulse input signal to the instrument cluster. Instrument cluster then converts 4-pulse input signal to a rectangular waveform and then sends input signal to Engine Control Module (ECM). ECM determines vehicle speed by using input signal. ECM may use input signal for controlling fuel injection system, electronically controlled automatic transaxle and various other systems. On models with traction control, ABS ECU may also be referred to as ABS & BA (Brake Assist) & TRAC & Vehicle Skid Control (VSC) ECU. On models without traction control, ABS ECU may also be referred to as ABS actuator and ECU. DTC is set if there is no vehicle speed signal to ECM while vehicle is being driven. Possible causes are:

Vehicle speed circuit is open or shorted between instrument cluster and ECM.
Defective instrument cluster.
Defective ECM.