Cruise control not working

[RR P38]

Damn cruise control is good on a long trip and i miss it.

So far i have checked the vacuum hoses and found that the hose on the accelerator pedal switch/plunger had a dodgy hose and connection, this is fixed now.
Cant see any problem with the vacuum actuator under the bonnet no rips or holes.
When i trigger the steering wheel button i can hear the relay click but i dont get any cruise control.

When the system died i had a few days/weeks were the system would only work above 100ks.

Any one have ideas on this problem?

[BusinessConnected]

I had similar issues and closer inspection on a number of the Cruise Control Hoses showed Microscopic Cracking etc where I assume they were leaking.

Being I didn't have a Local Repair Centre Handy I simply cover all the hoses in a couple of layers of Electrical Tape and it's been working fine ever since. (2+ Years)...

Reminds me I should try and purchase the proper hoses!!!

[adm333]

I assume you have also done a "reset" on the brake switch.

If so then you might consider replacing it. If not, this is my post from another thread....

By the sounds of it you may also have a faulty brake pedal switch.

In the first instance you can reset it. If its still a problem you can replace it fairly easily.

If you are taking off the drivers knee panel and instrument surround anyway, you should at leat try resetting it. In my experience you may also need to take off the lower panel above drivers footwell, that has the cabin light mounted in it.

The switch itself is best described as a plunger. It is spring loaded and when the cruise control is operating it is the sensor that tells the system you have applied the brake. If its faulty it tells the system you have applied the brake even when you haven't.

Reach up along the brake pedal shaft until you can feel the top of the plunger. Push the pedal down a few inches so its out of the way. You need to pull the plunger out towards the pedal and then gently release the pedal and let the pedal push the plunger back to its "Start" position. It has a sort or rachet feeling to it, like doing up a zip tie.

This will reset the switch.

Replacing the switch is easy too, it has a sort of bayonet action locking it into place, and the vacuum hose attaches to the end of it.

Dave

[Scouse]

There is a diagnosis procedure in the ETM on TOPIx.

[RR P38]

Cruise is working again...in a fashion. I can hold 110kmp/h anything under this and the speed slowly washes off.
Using the electrical fault diagnosis procedures i had an intermittent fault in the set switch. Ever so carefully i managed to resolder the contacts to the wire ribbon the micro switch sits on.
Im getting some funny Ohms readings for the cruise ECU tests.
Does anyone local to me have a Cruise ECU i could plug in to test my system?
Pretty sure that the BECM is ok by the checks that i have done, and everything else seems to check out ok.

[superquag]

For my RR Classic (95) I slavishly followed the RAVE proceedure. - To the letter... Especially regarding the brake pedal switch. - must be tested in place, NOT removed because its easier to get to etc...
And yes, its very finicky. Not a robust design, IMHO

It was leaking (perished) vacuum hoses and an out-of-adjustment brake switch in my case.

I understand the P38 and late Classics were similar regarding the Cruise Control.

[Craig_Keira]

If I were closer, I'd be happy to plug my Nanocom in, so we could see what wasn't working. Unfortunately, I don't foresee myself being in Sydney for the next few weeks at least.

[RR P38]

If I were closer, I'd be happy to plug my Nanocom in, so we could see what wasn't working. Unfortunately, I don't foresee myself being in Sydney for the next few weeks at least.

Thanks for the offer but im out of town for the next 4 weeks.
Im getting close to the problem.
Hawkeye doesnt show up faults.

[Sydr]

My cruise control was getting sulkier and sulkier; sometimes very reluctant. Switching the dash switch off for a while usually cleared it, but eventually it gave up completely. The electronic box had died, a new one was found which cleared the problem completely. I was told that this was the last NOS unit in Oz.

[Pierre]

Plenty of cruise control modules in UK - guaranteed and cheap.

Pete