Inspection Procedure 10
Inspection Procedure 10: Hunting (Repeated Acceleration and Deceleration) Occurs at the Set Vehicle Speed [TC-SST.]COMMENT
- The wheel speed sensor signal (vehicle speed signal) or the throttle body 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 throttle body.
- Malfunction of the ECM.
DIAGNOSIS PROCEDURE
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 diagnostic trouble code (DTC) may be set. Prior to this diagnosis, diagnose the CAN bus lines. (Refer to Trouble code diagnosis.) Testing and Inspection
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. Reading and Clearing Diagnostic Trouble Codes
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line. Reading and Clearing Diagnostic Trouble Codes
Q: Is the check result satisfactory?
YES : Go to Step 2
NO : Repair the CAN bus lines. 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. Reading and Clearing Diagnostic Trouble Codes
2. Turn the ignition switch to the "ON" position.
3. Check for ASC system DTC. (Refer to Diagnosis - Diagnostic Function.) Diagnostic Trouble Code Descriptions
Q: Is any DTC set?
YES : Repair the ASC system. 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. Reading and Clearing Diagnostic Trouble Codes
2. Turn the ignition switch to the "ON" position.
3. Check for MFI system DTC. (Refer to Diagnosis - Diagnostic Function.) Diagnostic Function
Q: Is any DTC set?
YES : Repair the MFI system. Then go to Step 6.
NO : Go to Step 4.
STEP 4. Using scan tool MB991958, check data list item 04: Vehicle speed.
1. Connect scan tool MB991958 to the data link connector. Reading and Clearing Diagnostic Trouble Codes
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to data reading mode for cruise control system. Reading and Clearing Diagnostic Trouble Codes
- Item 04: Vehicle speed.
Q: Is the check result satisfactory?
YES : Go to Step 5.
NO : Replace the ECM. When the ECM is replaced, register the encrypted code. Then go to Step 6.
STEP 5. Check the symptoms.
Q: Does hunting occur?
YES : Replace the ECM. When the ECM is replaced, register the encrypted code. Then go to Step 6.
NO : It can be assumed that this malfunction is intermittent.
STEP 6. Check the symptoms.
Q: Does hunting occur?
YES : Return to Step 1.
NO : The procedure is complete.