When I got my 1998 406 V6 saloon last October, the cruise control worked fine; I took the car off the road to do some work on it (e.g. changed the driver's side engine mountings, checked brakes etc.) I put the car on the road in January, but realised some time later that the cruise control had packed up. Quite honestly, I hardly ever use it anyway, but if it's fitted, I like it to work!. The car has done 115000 miles; the fuses look OK and if you suck the diaphragm thingy that operates the throttle, it works. There is no reference to it in the haynes manual, nor in the CD manual I got from Ebay. Would a fault code reader tell me the problem? Are there any other physical checks I can try - or any known faults on this system? Help, please!
J.A.
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PM0
Did you do anything in the dash area? Are the brake lights working?
There are switches on both the brake and clutch pedals; their function is best checked in live-data.
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Thanks for your interest! I just checked, and the brake lights are fine. The only thing I've done dashboardwise is to remove the aircon control panel to replace a blown bulb. I think this also required removing the radio cassette.
Excuse me for being dumb, but what do you mean by 'live data'?
Thanks,
J.A.
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PM0
Any chance that you disturbed the clutch pedal switch?
Live data is displayed on a scan tool and comprises all the info that the ECU is using.
Checking the actual electrical status of things like pedal switches when fault-finding is very useful.
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Now that weather has improved I've investigated the pedal area; not very accesible, is it? There is one switch on the clutch pedal and two on the brake pedal. All three appear to be working; i.e. the switch plungers are going in and out, and the connectors are still connected. Where would I find the 'scan tool' which you mentioned? I can get access to a fault code reader if that's any use; also not sure what you mean by 'checking the electrical status' of the switches - they don't appear on the wiring diagram of my Haynes manual! Sorry to sound so dumb - I'm really a nuts and bolts man - this new-fangled electricity stuff has me baffled! Seriously, any further advice and suggestions would be most welcome.
J.A.
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PM0
A scan tool is the very essential bit of kit that talks to ECU's. All sorts of makes - from about £1000 upwards.
Once communicating; you can see loads of useful stuff - including the stus of switches. [On or off.]
Most garages will have, at least access, to one. Get your cruise/engine ECU plugged in to one and see what's really happening in real time.
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More in hope than expectation I removed the steering column top shrouds to check the wiring on the cruise control stalk; unfortunately there is no plug on the stalk itself, only a four wire harness which disappears off under the dash somewhere, presumably to a plug and socket. Nevertheless, I sprayed the inside of the stalk with WD 40, wiggled the wires and woggled the stalk control in all directions, re-assembled it and, miracle of miracles it worked!! Don't know why, don't really care why! - but thanks to Screwloose for the suggestions which at least gave me a plan of attack.
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PM-0
Thanks for coming back with the outcome - handy stuff that WD40.
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Seems like I spoke too soon! - cruise control function remained a bit 'hit and miss' then a few days later the speedo began to stay at zero when moving from rest, then shoot up to speed above 20 mph or so. This got progressively worse, with a bit of odd engine running about 2000 rpm, then the speedo needle began to wave about as if demented. My son, who is a member of the 406 coupe club, kindly looked on their excellent tech. help pages, and came up with the most likely culprit - the speedo control unit (sometimes known as the Bitron unit?) part no: 1929SJ. The local dealer had one in stock - took about 15 mins to fit - all problems solved - touch wood!
Please note this only applies to the Phase One, D8 cars, the D9s have a different cure.
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