QuestionQUESTION: Need information on where to find info. Or repair manual for cruise
control. Have series III repair manual but cruise is not mentioned except
that it was an option. Have replaced bellows, engage switch, and
computer. All wiring checks and speed is in excess of 20 MPHwhen
engage is attempted. Please advise on any repair information available or
persons to contact. Can't seem to find German manfactures name.
Thank you.
ANSWER: Hi Dan,
You were correct that the factory manual left that out. I don't have a good test of the Cruise ECU but I do have a good wiring diagram of the system which I have used to diagnose problems with the Cruise system. I have not found many bad ECUs and have even been able to correct a few ECUs that have been off on engagement speed by opening the cover and adjusting the Pot while someone drives the car.
But if yours is not operating at all you need to test each component for it's connection to powers and grounds and that the speed generator signal is reaching the ECU. You also need to do all of your testing at a faster speed than 20 MPH. I do my testing with a Logic Probe as it will not interrupt the signals when testing.
It would be nice to have a test sequence to follow but I have been able to just test for powers and grounds and input signal and make repairs that way. Since you have already replaced the ECU and the actuator, all you need to do is test for powers, grounds and signals. Follow the diagram and test and you should find the problem.
The diagram is at http://mg-tri-jag.net/XJ-6Cruise1x1.jpg and the locate at http://mg-tri-jag.net/XJ-6Cruise21x1.jpg
Let me know,
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard because it is not a powered wire any ideas on what we should
read as far as a value to indicate that the connection is good between the
pulse generator and the ECU. We also need to check the yellow wire
under the brake pedal. Thank you
AnswerAs I said, I do all of my testing with a Logic Probe (LED) as it will not interrupt the signal. I have never tested the speedometer pulse generator with a volt meter so I don't know what kind of reading you will get. Since your speedometer is working all you need to do is put the car on a lift and have someone run it up to a speed and test the generator to see what the reading is. If it don't interrupt the signal then go to the ECU and test the Yellow wire at the ECU plug on the harness side to see if the signal is getting to the ECU. Or probe the wire on ECU side of the plug (green wire) to see that for sure the signal is going past the plug connector.
If your probe is not sharp enough to get through the insulation many mechanics push a straight pin through the wire and test at the straight pin. You do need to be careful not to let the pin contact a ground if you use that method.
If you will look at the diagram, you will see that the brake switch (not brake light switch) Is closed and when operated it opens. You can test the switch with the ohm meter section of your volt meter. You don't need to know what the voltage readings are. All you need to know is if the yellow and white wire at the ECU is getting connected to the actuator and pressing the brake pedal, breaks that connection.
All you need to do is follow the diagram and test each wire to see that it goes to where it is suppose to go and if there is a switch in between, see that the switch is connecting and disconnecting the circuit.
Howard
