That didn't fix it. Back to square one. The only thing left is the power switch and to test the plug going to the ECU. This sucks.

 

here is a process of elimination test for the D1 cruise control system, this test basically tests all components of the CC system EXCEPT FOR THE CC ECU, if all tests are completed and all the components are working then the CC ECU is most likely the culprit. you will need some basic electronics tools to perform these tests like a meter and a couple of fused jumpers.


1. Turn ignition on. Turn CC system on. Put transfer case in HI range and gearshift in forward gear. (from this point forward I will say "in drive" to mean the previous sentence). Ensure clutch pedal is released. Disconnect cruise control ECU connector. Connect negative lead of voltmeter to CC ECU harness connector terminal no. 8 (black wire) and positive lead to terminal no. 10 (orange/white wire). If battery voltage exists, go to step 3. If battery voltage does not exist, go to next step.

2. Turn ignition off. Using ohmmeter, check resistance between ECU harness connector term. no. 8 (black wire) and ground. If resistance is less than one ohm, go to next step. if resistance is not less that one ohm, repair black wire between CC ECU and ground.

3. Ensure ignition and CC system are on. Disconnect CC ECU connector. Using voltmeter, check voltage between CC ECU harness connector term. no. 4 (red/yellow wire) and ground. With RESUME/DECEL switch pressed, battery voltage should exist. With RESUME/DECEL switch released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified check circuit from steering wheel switch to CC ECU.

4. Ensure ignition and CC system are on. Ensure CC ECU connector is disconnected. Using voltmeter, check voltage between CC ECU harness term. no. 3 (gray/yellow wire) and ground. With SET/ACCEL switch pressed, batter voltage should exist. With SET/ACCEL switch released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, check circuit from steering wheel switch to
CC ECU.

5. Ensure ignition is on. Ensure CC ECU connector is disconnected. Using voltmeter, check voltage between CC ECU harness term no. 5 (green/purple wire) and ground. With brake pedal pressed, battery voltage should exist. With brake pedal released, no voltage should exist. If voltage is as specified, go to next step. If voltage is not as specified, check green/purple wire between CC ECU and stoplight switch. Check stoplight switch. Repair as necessary.

6. Turn ignition on. Reconnect CC ECU connector. Using voltmeter, back-probe between CC ECU harness term no. 11 (yellow wire) and ground. Spin a rear tire at about 3 MPH. Voltage should be about 2.5 volts, or vary between zero and 5 volts. If voltage is as specified, go to next step. If voltage is not as specified, check yellow
wire from CC ECU to the vehicle speed sensor. Check ECU. Repair as necessary.

7. Turn ignition on. Turn CC system on. Disconnect CC ECU harness connector. Connect a fused jumper wire between CC ECU harness term No. 1 (Orange/blue wire) and battery voltage. Connect another fused jumper wire between CC ECU harness term no. 7 (orange/red wire) and ground. If vacuum pump operates, go to
next step. If vacuum pump does not operate, check orange/blue and orange/red wires between CC ECU and vacuum pump. Check Vacuum pump. Repair as necessary.

8. Ensure ignition and CC system are on. Ensure CC ECU connector is disconnected. Connect a fuse jumper wire between CC ECU harness term. no. 1 (orange/blue wire) and battery voltage. Connect another fused jumper wire between CC ECU harness term. no. 7 (orange/red wire) and ground. Connect another fused jumper wire between CC ECU harness term. no. 6 (orange/pink wire) and ground. Vacuum pump should operate, valve should close and throttle should open wide. If system operates as specified, repair CC ECU. If system does not operate as specified, check orange/pink wire between CC ECU and vacuum pump. Check vacuum pump. Repair as necessary.

 

This is exactly what I need instead of changing parts until its fixed. I'd much rather diagnose the faulty part before shelling out $$$$$ to get it fixed. Again thanks.

 

Great write up Rover Chris. Spike could you make this a sticky please?

 

I can't take the credit as I did not write this, and unfortunately I can't give credit to who did as I don't know. I printed this out a couple years ago and determined with it that my ECU failed (and I think if I remember correctly that Spike had a buddy parting a rover out and sold me a new ECU) but with all that aside it should locate the problem.

I was getting my tools ready for my new job last week and came across this in my tool box! coincidence?

 

a little heads up when you go to unplug the CC ECU there is a metal retaining clip that goes around 3 sides of the plug, you will need a small screwdriver or pick tool to pop that clip off.

Also the CC ECU is mounted sideways behind the glove box and it is a pain to remove (shouldn't need to remove it unless you need to replace it like I did), I decided against trying to remount it back in the awkward location so I just zip tied it up above and have never had a problem with it since.

 

Yeah I figured out the clip when I slaved in a different ECU which didn't fix it. I thought I would do the same thing if I had been replacing it because it looked pretty tough to replace.

 

Thread back from the dead. HA. and a little help requested

I did the diagnostic test sequence posted above and everything checked out so I replaced the ECU with a used unit this morning, but no luck. There were 2 odd things that i think might be clues.
1. when probing the harness and spinning a wheel (to test the signal from the VSS) the meter started at 12 volts then dropped off to the appropriate range when the wheel was spinning. thought that was odd, stopped the wheel and tried it again, second time it all worked as described in the test.
2. yesterday before replacing the cruise ECU i took a ride and the cruise worked, until i went uphill, it acted like it was gonna keep up and then it just quit.

any ideas? skittish VSS? loose wire between the VSS and the cruise ECU?

i know if all ive got to complain about is the cruise control i should count myself lucky, but i just like to have things working. and it does make the 3 rides back home a little easier.

thanks
Adam

 

Do any of you who have replaced the ECU still have it on hand? Did you take a look at the Circuit board to see if it may have some bad solder joints like the famous window ECU?

 

ive got the "bad" one apart and in my hand right now, all the solder joints look ok, but there is a hint of melty plastic smell, though i dont see any obvious burn marks. im gonna bet that in my case ive got and intermittent signal from some input. its just gonna be a matter of running it down.

How many leads come off the VSS? and do they branch off somewhere? i guess im asking if im gonna have to rip the dash apart to trace this wiring.

thanks

adam