DI Cruise Control Gremlin
 

Well, I thought that I had the DI cruise control figured out on my 1999. Alas, it was not to be. I picked up a spare ECU at the wrecking yard last weekend. Got home today, rechecked all vacuum lines, all tight, even added a few hose clamps for good measure. Checked the brake switch, secure. Checked the air pump by hooking it up to an independant 12v source, working. Diaphram looked good, no apparent leaks, cuts or tears. With the key on the second position, I pushed the cruise control switch and heard a slight clicking from the Cruise ECU. I also substituted the spare ECU, same click. On the road test, I couldn't get the cruise to kick in with either ECU hooked up. When I first got the truck the cruise worked, although I needed to change out a few of the hoses. It then started to work occasionally and then essentially not at all. I tried it a couple of weeks ago and surprisingly it worked, right up intil I shut the truck off and then tried it again once I started it up again. Have tried it repeatedly since and no luck. I thought that I had narrowed the problem down to the ECU but after switching it out, that doesn't seem to be the problem. I have run out of options, I guess the only other possible missing link is the steering wheel switch. Is there a way to test it without replacing it?

1. all vacuum hoses appear to be secure
2. Air Pump is working
3. Brake Switch is secure in operational
4. ECU click when powered, spare also
5. Skateboard Switch lights up and clicks when depressed

I am getting to the limits of my technical skills. But this Discovery seems to take me to the limits and then pushes me over the edge! What is next?

Thanks in advance.

Phil
1999 DI
2001 DII

did you actually check the vacuum lines to ensure there are no holes or breaks? and also what about the bellows it could be cracked or not holding its pressure. then tehre is the obvious of the fuse... i only ask because i often find that what is messed up is the simple obvious stuff that i chose to believe couldnt be it, that and i dont know anything else about it... just sayin

I changed all of the hoses out with new material. Checked the fuse, it looked good, the other two items on the fuse are working, I think it is the mirrors and the rear windshield wiper. The only thing that I can't or don't know how to check is the switch on the steering wheel. At least thats is where I am today.......Phil

Follow elboy's thoughts and check the "actuator bellows", the vac line goes to it, it is mounted at the throttle body, you should be able to suck on the vac line and it should pull on the throttle and hold it's position, pretty easy to check.

You have to be going over 28 or something like that. You can hook a test light into the terminals on the ECU and see the signals from the switches. You can also see the pulses from the VSS. I went through mine and first found some bad traces on the board in the ECU. I re-soldered and it was better, but still intermittent. Everything was resolved after replacing the VSS. It was sending a weak signal. I could see it through the test light while driving, but it wasn't strong enough, apparently.

I will see if I can find the write up as to what you should be looking for on each pin at the ECu.

Here:

https://landroverforums.com/forum/sh...Cruise+control

Got home from work today and had about 5 minutes to try the next fix on the DI cruise control. The Diaphragm. I pulled the hose from the T that goes to the Diaphragm. Sucked in and viola, the Diaphragm pulled in. Put my finger over the hose and it held air, Diaphragm remainded "engaged." Well, eliminated that as a possible source of vacuum leak. this is really getting frustrating. Would the Cruise Control ECU "click" when the cruise control button is depressed if the ECU were bad? Any ideas, I hope to try the ECU connector voltage test if I can't otherwise figure it out before this weekend. thanks Phil

Heres an idea, how about a bad brake cancelation switch/ clutch switch? It holds vacuum and if it doesn't the system won't engage.

get yourself a vacuum pump and test the system.

You will hear a click when in park and turning on the switch. It is the lockout relay.

When the set button is pressed at speed, you should hear a quieter click. That is when it engages.

When you have some time, get a test light and put it on the pins I listed. Have a helper hold it on while driving, or you can use a rubber band. This will test all of the signals in.

Not to sound naive, when I test the connectors for the steering wheel mounted set/accl button, what will show with the test light? Will it be on all the time or only when one of the two buttons is depressed (actually pulled in the case of the steering wheel controls).

I will try the ecu "click" test at speed and see if I can hear anything.

The brake switch appears to be in good shape is firmly mounted and the hose to it is firmly secured and new. The odd part of this is that the cruise will work on rare occasions, although much less frequently as time goes on. It worked a couple of weeks ago, although I could only test it for about 4 miles or so on the freeway. I shut off the truck attended a basketball game and tried it again on the way home, nothing. that is what lead me to the ECU, if it were the hoses, diaphragm or even the pump, you'd think that if there were a leak, that it would work at all.

Thanks for the assistance, as someone said on the forum on a similar issue, "this is getting personal!" Phil

When you put the test light on the terminals, it will light up when a switch is pressed on the steering wheel, or brakes, etc... This will test all of the inputs.

If it works sometimes, you are probably looking at the solder joints on the ECU, wiring on the VSS or the VSS itsself.

You have to be going over 30MPH to get it to engage. If you have a weak signal from the VSS, your MPH will still show up on the dash, but the cruise won't work. If you have ever lost your MPH, replace the VSS.