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.
DIAGNOSTIC 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 Initial Inspection and Diagnostic Overview.)
STEP 1. Using scan tool MB991958, diagnose the CAN bus line.
(1)
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.
Connect scan tool MB991958 to the data link connector (Refer to Reading and Clearing Diagnostic Trouble Codes.)
(2)Turn the ignition switch to the "ON" position.
(3)Diagnose the CAN bus line (Refer to Scan Tool Testing and Procedures.)
Q. Is the check result satisfactory?
YES Go to Step 2
NO Repair the CAN bus lines CAN Bus Diagnostics 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 (Refer to Reading and Clearing Diagnostic Trouble Codes.)
(2)Turn the ignition switch to the "ON" position.
(3)Check for ASC system DTC Reading and Clearing Diagnostic Trouble Codes.)
Q. Is any DTC set?
YES Repair the ASC system Active Stability Control System (ASC).) 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 (Refer to Reading and Clearing Diagnostic Trouble Codes.)
(2)Turn the ignition switch to the "ON" position.
(3)Check for MFI system DTC Reading and Clearing Diagnostic Trouble Codes.)
Q. Is any DTC set?
YES Repair the MFI system Multiport Fuel Injection (MFI).) 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 (Refer to 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 (Refer to Scan Tool Testing and Procedures.)
- Item 04: Vehicle speed.
Q. Is the check result satisfactory?
YES Go to Step 5.
NO Replace the ECM [ Removal and Replacement.] Then go to Step 6.
STEP 5. Check the symptom.
Q. Does hunting occur?
YES Replace the ECM [ Removal and Replacement.] Then go to Step 6.
NO It can be assumed that this malfunction is intermittent How to Cope With Intermittent Malfunctions.)
STEP 6. Check the symptom.
Q. Does hunting occur?
YES Return to Step 1.
NO The procedure is complete.