Inspection Procedure 1: Communication Between Scan Tool and the ABS-ECU Is Not Possible

INSPECTION PROCEDURE 1: Communication between Scan Tool and the ABS-ECU is not possible.









CIRCUIT OPERATION
^ The diagnostic output is made from the ABS-ECU (terminal 13) to the diagnostic output terminal (terminal 7) of the data link connector.
^ When the data link connector's diagnostic test mode control terminal (terminal 1) is grounded, the ABS-ECU (terminal 4) will go into diagnostic mode.

TECHNICAL DESCRIPTION (COMMENT)
When communication with the scan tool is not possible, the cause is probably an open circuit in the ABS-ECU power circuit or an open circuit in the diagnostic output circuit.

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)
^ Blown fuse
^ Damaged wiring harness or connector
^ Malfunction of the hydraulic unit (Integrated with ABS-ECU)

DIAGNOSIS

Required Special Tool:
^ MB991223: Harness Set

STEP 1. Check the power supply circuit at ABS-ECU connector B-03.





1. Disconnect ABS-ECU connector B-03 and measure at the harness side.
2. Start the engine.
3. Measure the voltage between terminal 20 and ground. It should be approximately 12 volts (battery positive voltage).
Q: Is the voltage approximately 12 volts (battery positive voltage)?
YES: Go to Step 3.
NO: Go to Step 2.

STEP 2. Check the harness wire between the ignition switch (IG2) connector C-303 terminal 4 and ABS-ECU connector B-03 terminal 20.











NOTE: After inspecting the intermediate connector C-106, C-202, and C-203, inspect the wire. If the intermediate connector C-106, C-202 or C-203 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 3.





Q: Is the harness wire between the ignition switch (IG2) connector C-303 terminal 4 and ABS-ECU connector B-03 terminal 20 damaged?
YES: Repair it go to Step 5.
NO: Go to Step 5.

STEP 3. Check the harness wires between ABS-ECU connector B-03 terminal 4 and data link connector C-23 terminal 1, or ABS-ECU connector B-03 terminal 13 and data link connector C-23 terminal 7.











NOTE: After inspecting intermediate connectors C-02, C-104 and C-105, inspect the wires. If the intermediate connector C-02, C-104 or C-105 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 5.

Q: Is any of the harness wires between ABS-ECU connector B-03 terminal 4 and data link connector C-23 terminal 1, or ABS-ECU connector B-03 terminal 13 and data link connector C-23 terminal 7 damaged?
YES: Repair it go to Step 5.
NO: Go to Step 4.

STEP 4. Check the harness wires between ABS-ECU connector B-03 terminal 2 and ground, or ABS-ECU connector B-03 terminal 18 and ground.

Q: Is any of the harness wires between ABS-ECU connector B-03 terminal 2 and ground, or ABS-ECU connector B-03 terminal 18 and ground damaged?
YES: Repair it and then go to Step 5.
NO: Retest the system. If the malfunction persists, replace the hydraulic unit (integrated with ABS-ECU). Then go to Step 5.If the malfunction is not reproduced, then a transient malfunction is suspected.

STEP 5. Retest the system.
Q: Does the scan tool communicate with the ABS system?
YES: The procedure is complete.
NO: Return to Step 1.