Inspection Procedure 8
INSPECTION PROCEDURE 8: Tachometer does not WorkCIRCUIT OPERATION
The powertrain control module sends ignition signal to the combination meter via CAN bus line
TECHNICAL DESCRIPTION (COMMENT)
If only the tachometer does not operate, the power-train control module system may not be sending ignition signal, or the combination meter, the wiring harness or its connector may be defective
TROUBLESHOOTING HINTS
- Malfunction of the combination meter
- The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: Vehicle Communication Interface (VCI)
- MB991827: MUT-III USB Cable
- MB991910: MUT-III Main Harness A (Vehicles with CAN communication system)
STEP 1 Using scan tool MB991958, diagnose the CAN bus line
1. Connect scan tool MB991958 to the data link connector
2. Turn the ignition switch to "ON" position
3. Diagnose the CAN bus line
Q: Is the check result satisfactory?
YES: Go to Step 2
NO: Repair the CAN bus lines (Refer to Diagnosis in Information Bus,, Can Bus Diagnostic Chart) On completion, go to Step 3
STEP 2 Using scan tool MB991958, read MFI system diagnostic trouble code
Check if the MFI system DTC is set
Q: Is the DTC set?
YES: Diagnose the MFI system (Refer to MFI Diagnosis - Diagnostic Trouble Code Chart <28L ENGINE> or MFI Diagnosis - Diagnostic Trouble Code Chart <38L ENGINE>) On completion, in Computer and control Systems. go to Step 5
NO: Go to Step 3
STEP 3 Using scan tool MB991958, check data list
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958
1. Connect scan tool MB991958 to the data link connector
2. Turn the ignition switch to the "ON" position
3. Set scan tool MB991958 to the data reading mode
- Item 87: Tachometer
- The voltage should equal battery positive voltage
4. Turn the ignition switch to the "LOCK" (OFF) position
Q: Is the check result normally?
YES: It can be assumed that this malfunction is intermittent Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction
NO: Go to Step 4
STEP 4 Using scan tool MB991958, check actuator test
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958
1. Connect scan tool MB991958 to the data link connector
2. Turn the ignition switch to the "ON" position
3. Set scan tool MB991958 to the actuator test mode
- Item 84: Tachometer: 0 r/min
- The tachometer displays 0 r/min
- Item 85: Tachometer: 2000 r/min
- The tachometer displays 2,000 r/min
- Item 86: Tachometer: 5000 r/min
- The tachometer displays 5,000 r/min
4. Turn the ignition switch to the "LOCK" (OFF) position
Q: Is the check result normally?
YES: Go to Step 5
NO: Replace the combination meter
STEP 5 Retest the system
Check that the tachometer works normally
Q: Is the check result satisfactory?
YES: The procedure is complete (If no malfunctions are found in all steps, an intermittent malfunction is suspected Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction)
NO: Replace the combination meter