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Fault Diagnosis Procedures Now troubleshooting. You will need this FAST CHECK instrument to make a thorough check of the cruise control operation. But before you connect it into the system, begin by carrying out a road test, preferably with the owner, to determine the exact nature of the fault. You never know, it may simply be that he has not understood the operation of the system. During the road test, you should check the operation of the modes. ON, OFF, SET, RES, accelerating using SET, disengaging etc. A recommended road test is described in your Repair Manual From the road test, you should have ascertained one of 3 failure conditions: the car will not maintain cruise speed, the car will not resume or it does not disengage.

Having completed the road test, there are two checks to carry out before you fit the FAST CHECK equipment. First of all, disconnect the vacuum pipe from the pump. Depress the actuator fully and seal the end of the pipe. Now release the actuator. It should remain in the retracted position. If it does not, then check the integrity of the vacuum system, that is the pipes for leaks and security, the actuator and the sealing of the vent valves. Next check that the stop light switch operates satisfactorily and is adjusted correctly. Now connect the FAST CHECK instrument. Start by disconnecting the coil positive connector and the coil lead multiplug. Connect the white lead of the FAST CHECK to the harness white/black lead. Then connect the multiplug to the electronic control unit connector.

Move the switch to SPEED and switch on the ignition. Lamps, numbers 2 and 3 should illuminate. If lamp number 2 fails to illuminate, check the wiring continuity and the electronic control unit earth connection. If these are satisfactory, renew the speed sensor. If lamp number 3 does not illuminate, check the vent valve adjustment and wiring continuity. If these are satisfactory, replace the switch and vent valve. Next check that lamp number 3 extinguishes when the brake pedal is depressed. Repeat the test this time depressing the clutch pedal, if fitted. If the lamp does not extinguish in either case, check the appropriate vent valve and its wiring.

When correctly adjusted, the clearance between the vent valve body and the contact button should be 0.3 - 0.9 mm (0.012 - 0.035 in.). When this test is satisfactory, check that lamp number 3 extinguishes when the control switch is moved to OFF and released. If it does not, then there is a fault in the switch or its wiring. Now move the control switch to RES. Lamp number 5 should illuminate. If it does not, the control switch or its wiring is faulty. Next move the switch to SET. This time lamp number 1 should glow. Again if it does not, the switch or its wiring is at fault.

For your next check, rotate the switch between SPEED and VALVE. You should be able to hear the vacuum control unit operate. If it does not, check the wiring continuity first. If this is satisfactory, replace the vacuum control unit. Now move the switch to PUMP. You should hear the vacuum pump operate. If it does not, first check the wiring for continuity, then replace the vacuum control unit. Finally move the switch to OVERSPEED. If the lamp number 2 flashes and the overspeed relay can be heard to chatter, then replace the electronic control unit. If the lamp does not flash and the relay does not chatter, then replace the relay, having first checked the wiring for continuity.