Code No.P0578: Abnormal Voltage at Cruise Control Switches.



PROBABLE CAUSES



OPERATION


This circuit judges the signals of each switches (speed limiter ON/OFF, cruise control ON/OFF, CANCEL, SET - and RES +) of the cruise control switches. The engine-ECU detects the state of the cruise control switch by sensing the voltages shown below.


DIAGNOSIS CODE SET CONDITIONS




PROBABLE CAUSES




DIAGNOSIS PROCEDURE


STEP 1. Check the data list.


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

  • Item 75: CANCEL switch
  • Item 86: Cruise control ON/OFF switch
  • Item 91: RES - switch
  • Item 92: SET + switch
  • Item 174: Speed limiter main switch

Q. Is the check result normal?

Go to Step 19.
Go to Step 2.

STEP 2. Measure the terminal voltage at cruise control switch connector.


(1)Remove the cruise control switch from the steering wheel with the cruise control switch connector connected (Refer to ).
(2)Connect the negative battery terminal that was disconnected when the driver’s air bag module was removed.
(3)Turn the ignition switch to the "ON" position.
(4)Do not operate the cruise control switch.
(5)Measure the terminal voltage between cruise control switch connector terminal engine-ECU CNTS line and earth with cruise control switch connector connected.
OK: 4.7 - 5.0 V

Q. Is the check result normal?

Go to Step 11.
Go to Step 3.

STEP 3. Measure the terminal voltage at engine-ECU connector.



(1)Connect special tool power plant ECU check harness (MB992110) between the engine-ECU and the body-side harness connector.
(2)Turn the ignition switch to the "ON" position.
(3)Do not operate the cruise control switch.
(4)Measure the terminal voltage between special tool 48-pin connector terminal No.107 (engine-ECU connector terminal CNTS) and earth.
OK: 4.7 - 5.0 V

Q. Is the check result normal?

Go to Step 8.

Go to Step 4.

STEP 4. Check the harness wire for short circuit to earth between engine-ECU connector terminal CNTS and cruise control switch connector.


(1)Check the engine-ECU connector.
(2)Disconnect engine-ECU connector and measure at the harness connector side.
(3)Turn the ignition switch to the "LOCK" (OFF) position.
(4)Measure the continuity between engine-ECU connector terminal CNTS and earth.
OK: open circuit

Q. Is the check result normal?

Go to Step 18.
Go to Step 5.

STEP 5. Check the harness wire between engine-ECU connector terminal CNTS and clock spring connector, and between clock spring connector terminal and cruise control switch connector.



  • Check connector or harness wire for short circuit and damage.

Q. Is the check result normal?

Go to Step 6.
Repair connector or damaged harness wire. Then go to Step 20.

STEP 6. Check the clock spring.


Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring Inspection .

Q. Is the check result normal?

Go to Step 7.
Replace the clock spring, and install the driver’s air bag module [Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring ]. Then go to Step 20.

STEP 7. Check the cruise control switches.


Refer to .

Q. Is the check result normal?

Go to Step 10.
Replace the cruise control switches (Refer to ). Then go to Step 20.

STEP 8. Check the harness wire between engine-ECU connector terminal CNTS and clock spring connector, and between clock spring connector and cruise control switch connector.



  • Check connector or harness wire for open circuit and damage.

Q. Is the check result normal?

Go to Step 9.
Repair connector or damaged harness wire. Then go to Step 20.

STEP 9. Check the clock spring.


Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring Inspection .

Q. Is the check result normal?

Go to Step 10.
Replace the clock spring, and install the driver’s air bag module [Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring ]. Then go to Step 20.

STEP 10. Check the data list.


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

  • Item 75: CANCEL switch
  • Item 86: Cruise control ON/OFF switch
  • Item 91: RES - switch
  • Item 92: SET + switch
  • Item 174: Speed limiter main switch

Q. Is the check result normal?

Go to Step 19.
Go to Step 11.

STEP 11. Measure the terminal voltage at cruise control switch connector.


(1)Remove the cruise control switch from the steering wheel with the cruise control switch connector connected (Refer to ).
(2)Turn the ignition switch to the "ON" position.
(3)Press the cruise control ON/OFF switch with cruise control switch connector connected, and measure the terminal voltage between cruise control switch connector terminal engine-ECU SW- line and earth.
OK: 0.9 - 1.7 V

Q. Is the check result normal?

Go to Step 15.
Go to Step 12.

STEP 12. Measure the terminal voltage at engine-ECU connector.



(1)Connect special tool power plant ECU check harness (MB992110) between the engine-ECU and the body-side harness connector.
(2)Turn the ignition switch to the "ON" position.
(3)Press the cruise control ON/OFF switch, and measure the terminal voltage between special tool 48-pin connector terminal No.95 (engine-ECU connector terminal SW-) and earth.
OK: 0.9 - 1.7 V

Q. Is the check result normal?

Go to Step 13.

Go to Step 18.

STEP 13. Check the harness wire between engine-ECU connector terminal SW- and clock spring connector, and between clock spring connector and cruise control switch connector.



  • Check connector or harness wire for open circuit and damage.

Q. Is the check result normal?

Go to Step 14.
Repair connector or damaged harness wire. Then go to Step 20.

STEP 14. Check the clock spring.


Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring Inspection .

Q. Is the check result normal?

Go to Step 18.
Replace the clock spring, and install the driver’s air bag module [Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring ]. Then go to Step 20.

STEP 15. Check the harness wire between engine-ECU connector terminal SW- and clock spring connector, and between clock spring connector and cruise control switch connector.



  • Check connector or harness wire for short circuit and damage.

Q. Is the check result normal?

Go to Step 16.
Repair connector or damaged harness wire. Then go to Step 20.

STEP 16. Check the clock spring.


Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring Inspection .

Q. Is the check result normal?

Go to Step 17.
Replace the clock spring, and install the driver’s air bag module [Refer to GROUP 52B - Driver’s Air Bag Module and Clock Spring ]. Then go to Step 20.

STEP 17. Check the cruise control switches.


Refer to .

Q. Is the check result normal?

Go to Step 18.
Replace the cruise control switches (Refer to ). Then go to Step 20.

STEP 18. Check the data list.


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

  • Item 75: CANCEL switch
  • Item 86: Cruise control ON/OFF switch
  • Item 91: RES - switch
  • Item 92: SET + switch
  • Item 174: Speed limiter main switch

Q. Is the check result normal?

Go to Step 19.
Replace the engine-ECU (Refer to GROUP 13A - Engine-ECU <4B1>, GROUP 13C - Engine-ECU <4J1>). Then go to Step 20.

STEP 19. Read the diagnosis code.


(1)Use the M.U.T.-III, erase the diagnosis code of the cruise control system.
(2)Turn the ignition switch to the "ON" position, and press the cruise control ON/OFF switch to turn the cruise control system to ON (the cruise control indicator lamp <standard meter> or the cruise control display screen <high contrast meter> is turned on).
(3)After turning the cruise control system to ON, when 2 minutes or more has elapsed without operating the cruise control switches, read the diagnosis code of the cruise control system (Refer to ).

Q. Is diagnosis code No. P0578 set?

Replace the engine-ECU (Refer to GROUP 13A - Engine-ECU <4B1>, GROUP 13C - Engine-ECU <4J1>). Then go to Step 20.
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 20. Check the data list.


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

  • Item 75: CANCEL switch
  • Item 86: Cruise control ON/OFF switch
  • Item 91: RES - switch
  • Item 92: SET + switch
  • Item 174: Speed limiter main switch

Q. Is the check result normal?

Go to Step 21.
Return to Step 2.

STEP 21. Read the diagnosis code.


(1)Use the M.U.T.-III, erase the diagnosis code of the cruise control system.
(2)Turn the ignition switch to the "ON" position, and press the cruise control ON/OFF switch to turn the cruise control system to ON (turn ON the cruise control indicator lamp).
(3)After turning the cruise control system to ON, when 2 minutes or more has elapsed without operating the cruise control switches, read the diagnosis code of the cruise control system (Refer to ).

Q. Is diagnosis code No. P0578 set?

Return to Step 1.
The procedure is complete.