Inspection Procedure 2

INSPECTION PROCEDURE 2: Communication between the Scan Tool and the ABS-ECU is not possible.









CIRCUIT OPERATION
^ The DTC is set by the ABS-ECU (terminal 2) 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 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 are:
^ Blown fuse
^ Damaged wiring harness or connector
^ Malfunction of the brake modulator hydraulic unit (Integrated with ABS-ECU)

DIAGNOSIS
Required Special Tool:
^ MB991223: Harness Set

STEP 1. Check the power supply circuit. Measure the voltage at ABS-ECU connector B-118.





1. Disconnect ABS-ECU connector B-118 and measure at the harness side.
2. Start the engine.
3. Measure the voltage between terminal 10 and ground. It should measure battery voltage (approximately 12 volts).
Q: Is battery positive voltage (approximately 12 volts) present?
YES: Go to Step 4.
NO: Go to Step 2.

STEP 2. Check the following connectors.





^ ABS-ECU connector B-118





^ Junction block connectors C-210, C-211





^ Intermediate connector C-124
Check the connectors for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Are the connectors and terminals in good condition?
YES: Go to Step 3.
NO: Repair it and then go to Step 9.

STEP 3. Check the following harness wire.








The wire between junction block connector C-211 (terminal 2) and ABS-ECU connector B-118 (terminal 10)
Q: Is the harness wire damaged?
YES: Repair or replace it and then go to Step 9.
NO: Go to Step 9.

STEP 4. Check the ground circuit. Measure the resistance at ABS-ECU connector B-118.





Measure the resistance between terminal 12 and ground, and terminal 34 and ground. It should measure less than 2 ohms.
Q: Is the resistance 2 ohms or less?
YES: Go to Step 7.
NO: Go to Step 5.

STEP 5. Check the following connector.





ABS-ECU connector B-118 Check the connector, for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Are the connector and terminals in good condition?
YES: Go to Step 6.
NO: Repair it and then go to Step 9.

STEP 6. Check the following harness wires.








^ The wire between ABS-ECU connector B-118 (terminal 12) and ground (No.14)
^ The wire between ABS-ECU connector B-118 (terminal 34) and ground (No.14)
Q: Is any harness wire damaged?
YES: Repair or replace it and then go to Step 9.
NO: Go to Step 9.

STEP 7. Check the following connectors.





^ Data link connector C-14





^ Joint connectors C-23, C-101, C-105
^ Intermediate connector C-124





^ ABS-ECU connector B-118
Check the connectors for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Are the connectors and terminals in good condition?
YES: Go to Step 8.
NO: Repair it and then go to Step 9.

STEP 8. Check the following harness wires.








^ The wire between ABS-ECU connector B-118 (terminal 2) and data link connector C-14 (terminal 7)
^ The wire between ABS-ECU connector B-118 (terminal 5) and data link connector C-14 (terminal 1)
Q: Is any harness wire damaged?
YES: Repair or replace it and then go to Step 9.
NO: Replace the brake modulator hydraulic unit (integrated with ABS-ECU). Then go to Step 9.

STEP 9. Retest the system.
Q: Does the scan tool communicate with the ABS system?
YES: The procedure is complete.
NO: Return to Step 1.