Inspection Procedure 4: Brake warning light does not illuminate when the ignition switch is turned to ON position (engine stopped): Diagnosis

Required Special Tools: 

• MB991958: Scan Tool (M.U.T.-III Sub Assembly)
  • MB991824: Vehicle Communication Interface (V.C.I.)
  • MB991827: M.U.T.-III USB Cable
  • MB991910: M.U.T.-III Main Harness A

1. STEP 1. Using scan tool MB991958, diagnose the CAN bus line. 

   Use scan tool to diagnose the CAN bus lines.

   Q: Is the check result normal? 

   1. YES:  Go to Step 2.
   2. NO:  Repair the CAN bus lines (Refer to CAN BUS DIAGNOSTICS TABLE ).
2. STEP 2. Scan tool DTC 

   Use scan tool to check the DTC for the ABS system.

   Q: Is the DTC stored? 

   1. YES:  Carry out the diagnosis for the DTC (Refer to DIAGNOSTIC TROUBLE CODE CHART  ).
   2. NO:  Go to Step 3.
3. STEP 3. Scan tool other system DTC 

   Using scan tool, check that DTC U0141 is not stored by the combination meter system.

   Q: Is the DTC stored? 

   1. YES:  Troubleshoot the combination meter (Refer to Combination Meter - TROUBLE SYMPTOM CHART ), and then go to  Step 5.
   2. NO:  Go to Step 4.
4. STEP 4. Scan tool other system DTC 

   Using scan tool, check that DTC U0121 is not stored in the ETACS system.

   Q: Is the DTC stored? 

   1. YES:  Troubleshoot the ETACS (Refer to ETACS - DTC U0121: ASC-ECU CAN TIMEOUT ), and then go to Step 5.
   2. NO:  Replace the hydraulic unit (integrated with ABS-ECU) (Refer to HYDRAULIC UNIT  ), and then go to Step 5.
5. STEP 5. Retest the system. 

   Q: Does the brake warning light turn ON and OFF normally? 

   1. YES:  The procedure is complete.
   2. NO:  Return to  Step 1.