System Testing

The following diagnosis must be performed with tester 126-589-05-21-00 or equivalent or damage to cruise control system may result.
1. Disconnect 14 pin electrical connector from cruise control control unit. On 190D and E models, then control unit is attached to a plate located in the right hand front foot well. On all other models, the control unit is located under the left hand side of the instrument panel.
2. Connect tester 126-589-05-21-00 or equivalent to control unit 14 pin electrical connector.
3. Place ignition switch in the On position. If no faults are indicated, battery and ground LED symbols should be illuminated.
4. Depress LED test button on tester. All LED symbols except km/h should be illuminated. On 190D and E, 260E and 300CE, D, E and TE models with hall effect speed sensor installed on rear of speedometer, the km/h LED may be or may not be illuminated, depending upon position of speedometer magnet. If LEDs are not illuminated, check connection of tester to 14 pin connector. If tester is properly connected, proceed to next step.
5. If battery LED symbol is not illuminated, check for loose, damaged or improperly connected electrical connectors and wiring and correct as necessary. Also check control unit ground circuit and correct as necessary.
6. Check cruise control switch as follows:
a. Position cruise control switch in Accel, LED 1 and battery symbols should be illuminated.
b. Position cruise control switch in Decel, LED 2 and battery symbols should be illuminated.
c. Position cruise control switch in Off, LED 3 and battery symbols should be illuminated.
d. Position cruise control switch in Resume, LED 4 and battery symbols should be illuminated.
e. If LEDs is not illuminated for the indicated switch position, check for loose, damaged or improperly connected electrical connectors and wiring and correct as necessary. If electrical connectors and wiring are satisfactory, replace cruise control switch.
7. Depress tester M button. Accelerator pedal and linkage should move to the full throttle position and remain. If accelerator pedal does not move or if pedal cycles between full and closed throttle, check actuator and accelerator linkages for improper adjustment or binding. If linkages are satisfactory, check for loose, damaged or improperly connected electrical connectors and wiring and correct as necessary. If linkages and electrical connectors and wiring are satisfactory, replace actuator.
8. Depress and hold tester M button and allow accelerator pedal to move to the full throttle position, then depress brake pedal. Accelerator pedal should immediately return to the idle position. If accelerator pedal does not immediately move to the idle position, check actuator and accelerator linkages for improper adjustment or binding. If linkages are satisfactory, check for loose, damaged or improperly connected electrical connectors and wiring and correct as necessary. If linkages and electrical connectors and wiring are satisfactory, check stop lamp switch and replace as necessary. If linkages, electrical wiring and stop lamp switch are satisfactory, replace actuator.
9. On models with manual transmission, depress and hold tester M button and allow accelerator pedal to move to the full throttle position, then depress clutch pedal. Accelerator pedal should immediately return to the idle position. If accelerator pedal does not immediately move to the idle position, check actuator and accelerator linkages for improper adjustment or binding. If linkages are satisfactory, check for loose, damaged or improperly connected electrical connectors and wiring and correct as necessary. If linkages and electrical connectors and wiring are satisfactory, check clutch switch and replace as necessary.
10. Operate vehicle at speed below 30 MPH and note tester LEDs. Tester battery symbol should be illuminated and the km/h symbol should be illuminated or flashing. On model with electronic speedometer, if km/h LED symbol is not illuminated or flashing, replace speedometer. On models with hall effect speed sensor located at rear of speedometer, if km/h LED is not illuminated or flashing, replace hall effect speed sensor.
11. Disconnect tester.
12. Check wiring between actuator connector terminal 5 and control unit connector terminal 10 for ground. If wiring is grounded, repair or replace wiring as necessary. If wiring is satisfactory, check coding plug as described under ``Coding Plug Test,'' if equipped. If wiring and/or coding plug is satisfactory, replace control unit.
13. Reconnect control unit electrical connector and battery ground cable.