Cruise Control/Automatic Speed Control

[Merv]

My CC on the '88 is no longer working. It was before.   I did meter tests of the pins on the under dash control module and the brake and clutch switches are working fine and the module itself was replaced a few years ago. The #6 fuse is fine and the #3 relay seems fine.  This car has the electronic controller in the engine compartment.

So the two options I appear to be left with are: that the module is not good OR the lever/switch is faulty ( I get no change in resistance across the module relevant pins when it is activated).

Does this seem right or am I missing something?

[Peter M]

Merv,

Have you a wiring diagram to work from?

Your comments about the switch makes it sounds like it would be worth disconnecting and testing the contact continuity directly.

I know you are much brighter than me Merv but I ALWAYS struggle to remember which way the switch toggles and takes me a few goes to get it to activate.  Are you sure you are moving it in the right direction as surely not all the contacts would fail at once? 

Just had to ask......😁

[TINGY]

Are these the same unit used in the 944? Mine was a VDO unit and i went to our local VDO repairer in Newcastle and they didn't want a bar if it, they said it was too hard to diagnose why they actually fail and so i just left it. I left thinking that if there was some kind of electronic card in the workings somewhere, that would be hard to diagnose what had actually failed on the card.

[Merv]

Thanks guys.  Much appreciated.  Yes I have the full circuit diagrams for the 14 pin unit on the '88.

I pulled out the switch on the steering column this afternoon (how easy are these cars to work on!) and, after cleaning the contacts on the bench, tested all the functions UP (set) on DOWN (reset) and FOWARD to cancel. All worked fine.  Also checked the feed cable - all good.  So I am left with (1) the VDO module under the dash with its printed circuits and processors (I pulled that out also and checked the board and nothing obvious wrong or burned) and (2) the Control unit in the engine compartment. I think the VDO module is OK but who knows.

I will check out the Control unit in the engine area tomorrow.  Not feeling very 'bright' at all Peter.

[Peter M]

1 hour ago, Merv said:

functions UP (set) on DOWN (reset) and FOWARD to cancel.

Thanks Merv, I've learnt a better way than my usual fumblings!

Have you done some searches on Pelican?  I recall there are a number of threads on tempostat repair.

[Merv]

Read them all thanks Peter.

[Merv]

This saga continues.  I swapped out the Cruise Control module with a known good one and no difference.  Check the brake switches, clutch switch, relays, fuses and tested the steering column CC switch. All fine. I think that there is a broken wire somewhere. 

[Merv]

Have been through all the settings again on my meter and everything checks out.  Just no power coming from the steering column switch for the cruise control.  Has anyone got a spare used one that I can buy to try?

91161310201

[Merv]

Tried another column switch but no change. Now for the dreaded clutch switch. On the RHD cars what is the easiest way to access it?

[Big Dav]

I had to adjust the clutch switch a few years back after lowering the clutch pedal height a tad (caused the CC to not engage because of the switch position).  It was a bit of a brute to get to and from memory required partially removing the centre console and the passenger floorboard.  The space is tight and its right under the metal console support in a tunnel with some access holes and hard to get a tool on it.  Doable but not a five minute job that it probably is on a LHD car. It was enough for me just to loosen the switch body and slide it a few mm and re-tighten to get it working again.

If I remember correctly if I tried to engage the CC it would still make a clicking noise in the module under the dash even though the clutch switch would prevent it from working.  Does your module make a clicking noise when you try to engage it on the road?

[Merv]

Thanks Dav. I hear it is a pain of a job. Your experience helps. No klicking noise at all. Replaced the module under the dash as well. I am being stubborn but if the system is there, it should work! The servo in the engine compartment is the last suspect. 

[Big Dav]

1 hour ago, Merv said:

 I am being stubborn but if the system is there, it should work!

I agree!  I simply have to have everything working correctly.  I think for any decent highway journey having working cruise control is great, particularly with speed cameras, average speed sections etc etc

On second thoughts maybe it DIDN'T click when the clutch switch was out of adjustment. I might have given the wrong information above.  Hopefully an adjustment or a new switch will do the job. 

[Merv]

Thanks Dav.  I agree the CC adds a safety margin with cameras if you have calibrated your speedo (via GPS). I asked the above question on a UK forum about CC problems and they just laughed.  No one there cares if it works or not.  In big countries however, we do care.

[Merv]

I pulled out the console (who ever designed that component should be shot.  It is such  flimsy poorly put together item) and check the clutch switch in the tunnel and also via the 85 pin on the CC relay.  It works perfectly. Back to the drawing board then. Not sure where to go next with this (changed under-dash module, steering column switch, checked all 14 pins on the module connector, etc.)  It could be the servo in the engine compartment but it seems as though no power is getting to the system.

 

Should the red relays emit and audible click?

[Big Dav]

I just checked my car whilst stationary in the garage.  With just the ignition turned on I can hear an audible click from the under dash module whenever I push the CC switch around ie: resume (down), cancel (pull) or set (up).  Also after a click from resume or set if I push the brake pedal in it clicks again.  I don't get the same noise if I push the clutch in though.  Not sure about relays in the frunk. It's quiet out there but didn't really notice anything else.  

Mine's an '87 so is vacuum operated in the engine bay but I presume the switch and module are the same as yours.  

[Merv]

Thanks Dav. Much appreciated. This is the second under dash module I have tried. All the module pins seem to check out otherwise on the 88 specs. The power to the module seems to be an issue and the usual suspects (clutch switch, brake switches, LED bulbs with low draw, etc) all seem to be out of the equation at this stage.  Back to the diagram and the main cable harness I suspect.  

[Merv]

Solved!  I think I now know the CC system on these cars extremely well.  Checked clutch cut out switch, brake cut out switch, exchanged CC module with a  known good one, exchanged steering column switch with a known good one, tested CC relay and fuses ... etc.  The unit just wasn't getting power. Finally pulled out the fuse box and found the power wire underneath to the CC relay was disconnected.  All perfect now and holds speed well. What a saga.

[firstone]

Well done. You always see these things through.

[Merv]

Stubbornness helps!  Now for the pesky remote central locking on the 996 Turbo.

 

[Big Dav]

Well done.  There's nothing like fixing something like that yourself!

[Merv]

I hate to think what it would have cost in a repair shop Dav.  The CC on these cars is notorious for being hard to problem solve. Big thanks also to Damien for his help.