Inspection Procedure 7: Hunting (Repeated Acceleration and Deceleration) Occurs at the Set Vehicle Speed.

COMMENTS ON TROUBLE SYMPTOM

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 ABS-ECU <vehicles without TCL/ASC> or TCL/ASC-ECU <vehicle with TCL/ASC> to the engine-ECU <M/T> or engine-A-M/T-ECU <Automated manual transmission> via the CAN bus line.

PROBABLE CAUSES

Malfunction of CAN bus system.
Malfunction of the ABS system <vehicles without TCL/ASC>.
Malfunction of the TCL/ASC system <vehicles with TCL/ASC>
Malfunction of the throttle body.
Malfunction of the MPI system.
Malfunction of the engine-ECU <M/T>.
Malfunction of the engine-A-M/T-ECU <Automated manual transmission>.

DIAGNOSIS PROCEDURE

caution

If there is any problem in the CAN bus lines, an incorrect diagnosis code may be set. Prior to this diagnosis, diagnose the CAN bus lines.
Before replacing the ECU, ensure that the CAN bus lines is normal.

STEP 1. Check the CAN bus system diagnosis.

Using M.U.T.-III, perform CAN bus diagnosis (Refer to GROUP 54C - Explanation About The M.U.T-III Can Bus Diagnostics

Q. Is the check result satisfactory?

	Go to Step 2 <vehicles without TCL/ASC>.

	Go to Step 3 <vehicles with TCL/ASC>.

	Repair the CAN bus lines (Refer to GROUP 54C - Troubleshooting, Can Bus Diagnostic Table ). Then go to Step 7.

STEP 2. Check the ABS system diagnosis code <vehicles without TCL/ASC>.

Using M.U.T.-III, perform ABS system diagnosis code (GROUP 35B - Troubleshooting, Diagnostic Function

Q. Is any diagnosis code set?

	Repair the ABS system (Refer to GROUP 35B - Troubleshooting, Diagnosis Code Chart ). Then go to Step 7.

	Go to Step 4.

STEP 3. Check the TCL/ASC system diagnosis code <vehicles with TCL/ASC>.

Using M.U.T.-III, perform TCL/ASC system diagnosis code (GROUP 35C - Troubleshooting, Diagnostic Function

Q. Is any diagnosis code set?

	Repair the ASC system (Refer to GROUP 35C - Troubleshooting, Diagnosis Code Chart ). Then go to Step 7.

	Go to Step 4.

STEP 4. Check the MPI system diagnosis code.

Using M.U.T.-III, perform MPI system diagnosis code (Refer to GROUP 13B - Troubleshooting, Diagnosis Function

) <135, 4A9> or (Refer to GROUP 13C - Troubleshooting, Diagnosis Function

) <4G1>.

Q. Is any diagnosis code set?

	Repair the MPI system (Refer to GROUP 13B - Troubleshooting, Inspection Chart for Diagnosis Trouble Code ) <135, 4A9> or (Refer to GROUP 13C - Troubleshooting, Inspection Chart for Diagnosis Trouble Code ) <4G1>. Then go to Step 7.

	Go to Step 5.

STEP 5. Check the data list.

Using M.U.T.-III, check the data list (Refer to

- data list reference table).

Item 04: Vehicle speed signal

Q. Is the check result normal?

	Go to Step 6.

Replace the engine-ECU <M/T> or engine-A-M/T-ECU <Automated manual transmission> (Refer to GROUP 13B - Engine-ECU, engine-A-M/T-ECU

) <135, 4A9> or (Refer to GROUP 13C - Engine-ECU

) <4G1>. When the engine-ECU <M/T> or engine-A-M/T-ECU <Automated manual transmission> is replaced, register the encrypted code (Refer to GROUP 54A - Ignition Switch, Encrypted Code Registration Criteria Table

). Then go to Step 7.

STEP 6. Retest the system

Q. Does a hunting occur?

Replace the engine-ECU <M/T> or engine-A-M/T-ECU <Automated manual transmission> (Refer to GROUP 13B - Engine-ECU, engine-A-M/T-ECU

) <135, 4A9> or (Refer to GROUP 13C - Engine-ECU

). Then go to Step 7.

	It can be assumed that this malfunction is intermittent (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points, How to Cope with Intermittent Malfunction ).

STEP 7. Retest the system

Q. Does a hunting occur?

	Return to Step 1.

	The procedure is complete.