1: Communication Between Scan Tool & ABS-ECU Is Not Possible

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





Part 1 of 2





Part 2 of 2

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-118.
1) Disconnect ABS-ECU connector B-118 and measure at the harness side.
2) Start the engine.
3) Measure the voltage between terminal 20 and ground.
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) and ABS-ECU connector B-118

NOTE: After inspecting the intermediate connector C-122, C-210 and C-211, inspect the wire. If the intermediate connector C-122, C-210 or C-211 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) and ABS-ECU connector B-118 damaged?
YES: Repair it and go to Step 5.
NO: Go to Step 3.








STEP 3. Check the harness wires between ABS-ECU connector B-118 and data link connector C-14.

NOTE: After inspecting intermediate connectors C-19, C-105, C-122 and C-124, inspect the wires. If the intermediate connector C-19, C-105, C-122 or C-124 is damaged, repair or replace it. If the connector has been repaired or replaced, go to Step 4.

Q: Is any of the harness wires between ABS-ECU connector B-118 and data link connector C-14 damaged?
YES: Repair it and go to Step 5.
NO: Go to Step 4.





STEP 4. Check the harness wires between ABS-ECU connector B-118 and ground.
Q: Is any of the harness wires between ABS-ECU connector B-118 and ground damaged?
YES: Repair it and then go to Step 5.
NO: Go to Step 5.

STEP 5. Check symptoms.
Q: Does the scan tool communicate with the ABS system?
YES: This diagnosis is complete.
NO: Return to Step 1.