P38A Cruise control for 1998.

J L Carr · Apr 28, 2022

Hi Guys, still having problems with my cruise control but can somebody tell me if this is the right ECU for my car as there seems to be 2 of them, picture 1 fitted to my car, picture 2 is one I've found but my question is will this still fit. Thanks.

Unless the black one is hidden somewhere else as the silver one is under the drivers side panel.

DanClarke · Apr 28, 2022

Can't tell you about the silver white package but my MY2000 has those two other parts (the Red & Black boxes pictured).
Plus I have duplicates/spares in case they go pop.

kermit_rr · Apr 28, 2022

Is yours a Thor? If so it's the latter type.
What's the problem you're having?

J L Carr · Apr 28, 2022

It has stopped working about 6 months ago, so I changed both the red relay and the ecu unit and nothing so then changed the cruise control unit by the throttle cable but still nothing, so took the lid off the cruise unit and added power and it clicked. Went to work the next day and it worked in the morning but that was it, so that why I was asking about the black ecu, but mine not a thor motor but a gems.

kermit_rr · Apr 28, 2022

I don't know how the gems works. Does it have the vacuum pipe to the switch on the brake pedal?

tomcat59alan · Apr 28, 2022

kermit_rr said:
I don't know how the gems works. Does it have the vacuum pipe to the switch on the brake pedal?

I think your right Kermie, well it was on mine.the vacuum pipes tend to crack

kermit_rr · Apr 28, 2022

tomcat59alan said:
I think your right Kermie, well it was on mine.the vacuum pipes tend to crack

On mine it was both, pipe was leaving and the switch wasn't secure on the pedal so thought the brake was always on

J L Carr · Apr 28, 2022

tomcat59alan said:
I think your right Kermie, well it was on mine.the vacuum pipes tend to crack

Replaced the whole pipe from the brake switch to the cruise control and also renewed the switch at the same time,so everything got changed apart for the electrics.

Marshall8hp · Apr 29, 2022

The silver Hella unit and red relay are the correct ones for your car. You can fit the later one, you will need the later plug, de-pin yours and pin out the new one.

Generally the Hella ones work a little more accurately than the later ones, i.e. better at keeping the set speed.

domino · Apr 30, 2022

Checked the vac hoses under the bonnet? They tend to split.

J L Carr · Apr 30, 2022

domino said:
Checked the vac hoses under the bonnet? They tend to split.

Changed the whole lot including the ones around the bellow,so like I said replaced everything apart the electrics so it's a puzzle driving me mad.

DanClarke · Apr 30, 2022

Changed the brake switch and/or checked it is set correctly?

J L Carr · Apr 30, 2022

DanClarke said:
Changed the brake switch and/or checked it is set correctly?

New brake switch as I said earlier but all it does is clip into place or have I got that wrong as my old one seemed to stick so far down pushing the pin down.

Marshall8hp · Apr 30, 2022

There are two brake switches and both have to be right. There is the vacuum one that dumps the vacuum for the CC and there is the one for the brake lights. Both interact to cancel the cruise control and both have to mounted correctly. They quite often break one of the mounting lugs. I had exactly your problem some years ago, and I found that if I put my toes under the brake pedal and lifted it towards me as hard as I could, the CC would work. Turned out to be the brake light switch was dicky, replaced that and never had an issue since.

kermit_rr · May 1, 2022

The cruise control switch has to be adjusted.
Press the plunger all the way in with your finger, then pull it all the way out. It's on a self assisting ratchet so quite hard to pull but it will do a few clicks and come to a firm stop.
Press the brake pedal all the way down, refit the switch then release the pedal

Mark Piercy · May 1, 2022

How come the petrol setup doesn't use an ecu to deal with the cruise like the diesel does?
Relying on sensors and so on or was it a requirement for certain countries?

DanClarke · May 1, 2022

Mark Piercy said:
How come the petrol setup doesn't use an ecu to deal with the cruise like the diesel does?
Relying on sensors and so on or was it a requirement for certain countries?

It does. There's a black Hella ECU and the red voltage regulating box on my 2000 4.6 Thor.

Mark Piercy · May 1, 2022

DanClarke said:
It does. There's a black Hella ECU and the red voltage regulating box on my 2000 4.6 Thor.

Cheers Dan , so why additional vacuum pipes?
Odd dont you think ?

DanClarke · May 1, 2022

Mark Piercy said:
Cheers dam, so why additional vacuum pipes?
Odd dont you think ?

I'm not sure about "additional" Mark......because I have never seen anything different.

I replaced all my rotted rubber with silicone, still doesn't work properly.
Set the switch, changed the ECU & regulator box, still doesn't work except on the flat at 50-55mph where you feel it slightly pulling the accelerator out from under your foot.
Next stop the main vacuum and bellows assembly (I have a spare) I don't often even try to use cruise, but its the one thing not working on the whole car.

kermit_rr · May 1, 2022

I don't see the purpose of it. If you keep the switch depressed then the cruise still works normally. When I first got the car, i taped up the switch as i couldn't get it fitted. Cruise worked perfectly and still turned off when i touch the brakes, ie the brake light switch was triggered
Assume it's a backup incase the brake light switch fails, the cruise vacuum is dropped. Not sure about the electrical connection, purely to measure the switch position?

P38A Cruise control for 1998.

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