Inspection Procedure 6
INSPECTION PROCEDURE 6: Hunting (Repeated Acceleration and Deceleration) Occurs at the Set Vehicle Speed.COMMENT
The wheel speed sensor signal (vehicle speed signal) or the MFI system is suspected.
The wheel speed sensor signal (vehicle speed signal) is transmitted from the ASC-ECU to the ECM via CAN bus line.
TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CASE:)
- Malfunction of the CAN bus line system.
- Malfunction of the ASC system
- Malfunction of the MFI system
- Malfunction of the ECM.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
CAUTION:
- If there is any problem in the CAN bus lines, an incorrect DTC may be set. Prior to this diagnosis, diagnose the CAN bus lines.
- Whenever the ECM is replaced, ensure that the CAN bus lines are normal.
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
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. Scan Tool Connecting
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line. How to Diagnose the CAN Bus Line
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991958.
Q: Is the check result satisfactory?
YES : Go to Step 2
NO : Repair the CAN bus lines (Refer to Controller Area Network, Diagnosis-Can Bus Diagnostic Chart). Then go to Step 6.
STEP 2. Using scan tool MB991958, check for ASC system DTC.
1. Connect scan tool MB991958 to the data link connector. Scan Tool Connecting
2. Turn the ignition switch to the "ON" position.
3. Check for ASC system DTC (Refer to Active Skid Control System (ASC), Diagnosis-Diagnostic Function).
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991958.
Q: Is any DTC set?
YES : Diagnose the ASC system (Refer to Active Skid Control System (ASC), Diagnosis-Diagnostic Trouble Code Chart). Then go to Step 6.
NO : Go to Step 3.
STEP 3. Using scan tool MB991958, check for MFI system DTC.
1. Connect scan tool MB991958 to the data link connector. Scan Tool Connecting
2. Turn the ignition switch to the "ON" position.
3. Check for MFI system DTC (Refer to MFI, Diagnosis-Diagnostic Function). Diagnostic Function
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991958.
Q: Is any DTC set?
YES : Diagnose the MFI system (Refer to MFI, Diagnosis-Diagnostic Trouble Code Chart). Diagnostic Trouble Code Descriptions Then go to Step 6.
NO : Go to Step 4.
STEP 4. Using scan tool MB991958, check data list item 4: Vehicle speed.
1. Connect scan tool MB991958 to the data link connector. Scan Tool Connecting
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to data reading mode for cruise control system. Reading Diagnostic Trouble Codes
- Item 4: Vehicle speed.
4. Turn the ignition switch to the "LOCK" (OFF) position.
5. Disconnect scan tool MB991958.
Q: Is the check result satisfactory?
YES : Go to Step 5.
NO : Replace the ECM [Refer to MFI, Engine Control Module (ECM)]. When the ECM is replaced, register the encrypted code (Refer to wireless control Module, Diagnosis-ID Code Registration Judgment Table). Then go to Step 6.
STEP 5. Retest the system
Q: Does hunting occur?
YES : Replace the ECM [Refer to MFI, Engine Control Module (ECM)]. When the ECM is replaced, register the encrypted code (Refer to Wireless Control Module, Diagnosis-ID Code Registration Judgment Table). Then go to Step 6.
NO : It can be assumed that this malfunction is intermittent (Refer to General (Body and Chassis), How to Use Troubleshooting/Inspection Service Points-How to Cope with Intermittent Malfunction).
STEP 6. Retest the system
Q: Does hunting occur?
YES : Return to Step 1.
NO : The procedure is complete.