Inspection Procedure 32

INSPECTION PROCEDURE 32
Anti-lock Brake Signal System
Anti-lock Brake Signal Circuit




WIRING DIAGRAM and CONNECTOR VIEW

CIRCUIT OPERATION
- The battery positive voltage is applied on the ABS-ECU from the ECM (terminal 44) via the resistor in the ECM.
- The ABS-ECU turns the power transistor in the ABS-ECU unit "ON" when the motor relay is driven and grounds the terminal to which the battery positive voltage is applied. With this, the voltage in the ECM changes from high to low and the ECM detects that the ABS-ECU is driving the motor relay.

TROUBLESHOOTING HINTS
The most likely causes for this case:
- Improper connector contact, open circuit or short-circuited harness wire.
- Malfunction of the ABS-ECU.
- Malfunction of the ECM.

DIAGNOSIS




STEP 1. Check the circuit at the ABS-ECU connector A-85.
(1 Disconnect connector A-85 and measure at the harness side.
(2) Turn the ignition switch "ON."
(3) Measure the voltage between terminal 6 and ground.
- Voltage should be approximately 12 volts (battery positive voltage)
(4) Turn the ignition switch "OFF."
If not within specifications, go to Step 2.
If within specifications, go to Step 4.







STEP 2. Check the harness wire between the ECM connector C-53 and the ABS-ECU connector A-85.
If the wire between the ECM connector C-53 and the ABS connector A-85 is not damaged, go to Step 3.
If the wire between the ECM connector C-53 and the ABS connector A-85 is damaged, repair it. Then confirm that the malfunction symptom is eliminated.




STEP 3. Check harness connector C-53 at the ECM for damage.
If harness connector C-53 is damaged, repair or replace it. Refer to Harness Connector Inspection.
If harness connector C-53 is in good condition, replace the ECM.
Then confirm that the malfunction symptom is eliminated.




STEP 4. Check the circuit at the ECM connector C-53.
(1) Start the engine.
(2) With the connector connected, measure the voltage between the terminal 44 and the ground.
(3) Slowly accelerate the vehicle and inspect the section where the vehicle speed changes from 0 km/h (0 mph) to 10 km/h (0.6 mph). The ABS-ECU performs a self check one time only after engine start and above 10 km/h (6 mph).
- The voltage should temporarily drop from 12 volts (battery positive voltage) to 0 - 3 volts.
(4) Turn the ignition switch "OFF."
If not within specifications, check the ABS-ECU connector A-85 and repair or replace as needed Refer to Harness Connector Inspection. If the ABS-ECU connector A-85 is correct, replace the ABS-ECU.
If within specifications, replace the ECM.
Then confirm that the malfunction symptom is eliminated.