cruise control stops working randomly

I have a 2002 Chrysler Concorde Lxi 3.5L V6. Sometimes, the cruise control will shut off and I won't be able to turn it back on until I restart the car.

It happens if I have it on and running and then disable it by hitting the brake or if I've just turned it on and hit the "set" button. Sometimes, I won't have to do anything, I'll just be driving along at

70mph and the cruise control will just shut off. In each case, the green "cruise control" light on the dash shuts off.

If anybody has any suggestions as to what may be going on, I'd appreciate hearing them.

Thanks, PaulH

Reply to
PaulH
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A scan tool will be needed to find out what the inputs and outputs are doing and will also show what the last cutout was

Glenn Beasley Chrysler Tech

Reply to
maxpower

This won't be an exact answer, but we've seen an indication recently on the 300M Club forums (for this discussion, 300M = Concorde), that the brake switch needs replacing when this happens.

Nothing definite has been determined (by repeated success), but the switch does have three contacts - two of which are inputs to the PCM for purposes of controlling the cruise control. One of those contacts makes and breaks a bit of current (for the cruise control servo unit solenoid valves) and has a tendency to burn and get intermittent. When the PCM does not see the two cruise control-related contacts (the other one is the low-current brake sense signal to deactivate the cruise control when the brakes are applied) work pretty much in tandem (due to the one not consistently making electrical contact) as they normally would, for safety liability concerns, it disables the cruise control (simultaneously, the light on the dash turns off and power to the servos is cut off). Just a theory so far, it's the only explanation that makes sense, and, like I said, appears to be supported by success in replacing the brake switch for people who have this problem, which there have been a few of lately.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

On Tue, 09 Oct 2007 17:31:58 -0400, Bill Putney writ:

Might the same diagnosis (brake switch) apply to a '94 LHS?

My cruise comes on for a few seconds, then shuts off.

Reply to
freemont

I can't say for sure. I have two 2nd gen. Concordes. The 1st gen. LH's are probably very similar, but I'd have to see their schematics.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

When the set switch is pressed the cruise control lite should turn on reminding you that the cruise control is on. When the brake is depressed , it shuts the cruise servo off. BUT the lite on the dash should still alert you that the cruise control is still on. So what you are saying is the brake switch is replaced because the cruise (dash lite turns off) or the fact that the cruise control just kicks out???

Glenn

Reply to
maxpower

Glenn, You are correct that when things are working normally and you hit the brakes, the dash light stays on, and the cruise "kicks out" (with dash light still on). However, when this switch contact gets flaky, the PCM apparently senses that something is amiss (because it sees the two contacts not operating in tandem like they normally would), so the PCM turns the cruise completely off - yes - the dash light goes out. I figure this is an anti-liability feature they built into the PCM firmware that takes such action if it notices *any* anomalies whatsoever to avoid any possibility of anything resembling disasterous "sudden aceleration" situations and creating a lot of bad publicity, accidents, lawsuits, etc. (think "Audi 5000").

Again, this is speculation, but appears to be borne out by the problem being corrected when the switch is replaced. A guy on the 300M forums turned us on to this by observing that that particular contact appeared burnt when he was having this problem and he examined the brake switch, plus, the problem went away when he replaced the switch.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

Also, Glenn - I was just looking thru the PCM codes list, and there are several codes specific to the cruise control. They're worded so ambiguously as to be hard to know if they relate to the brake switch failure. I notice that they do not set the CEL. So your advice to have the codes read may be right on.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

You know, I get a lot of advice to have the OBD II port read. I'll hit AutoZone and have them do it. But, is there a good reader you recommend?

Thanks, PaulH

Reply to
PaulH

Not only to read the codes but also check to see what the last cut out was. Its a feature that our scan tool has, it will show if the brake switch, power switch,speed or ignition caused it to cut out. The same goes with vehicle theft alarm.it will show what triggered the alarm. But reading the inputs and outputs in the cruise control monitor should determine what the cause was. The next time I work around a brake switch with cruise I will disconnect the switch with the cruise on to see if the lite on the dash goes off. Im just not sure

Glenn

Reply to
maxpower

Unless you snip a wire to separately disconnect one of the two switches related to cruise control, I don't think that will do anything as far as confirming or refuting the theory. If you simply unplug the switch connector, both switches will appear to be open - the PCM will simply say to itself "Oh - the brake is on" (with both switches simultaneously agreeing to that) - it will keep the cruise power and dash light on. My theory is that it looks for **discrepancies (differences)** between what the two switcnes are telling it (i.e., one switch appearing to be open and the other appearing to be closed at the same time).

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

looking at the wire diagram, snipping any wire at the switch doesn't give me a reason to think the dash lite will go out

Reply to
maxpower

Then you missed what I was saying earlier. Snipping a switch wire will not cause the light to go out directly. BUT if the PCM firmware is looking at the two contact closures and openings to not be agreeing with each other as a reason to shut the cruise control off as a safety/liability precaution, then - yes - it would shut it down and the light off.

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

The brake lamp switch has three internal switches

Brake lamp actuation Speed control deactivation, and Brake sense for ABS and brake transmission shift interlock

The PCM just wants to see (brake sense circuit) , cut that wire, the lite on the dash will still be lit and you wont have cruise control. with a possible fault code stored

Reply to
maxpower

If the fault code gets stored, the PCM won't cut the cruise control (and dash light) off?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

simultaneously

If the fault code is stored with an active (hard fault) the cruise will not work anyhow, the lite on the dash will still be on. Customer complaint is cruise will not work. If the switch or circuit from the switch has a problem the dash lite will not come on.

Reply to
maxpower

OK - makes sense. So we're left wondering what would cause the light to turn off (along with the cruise control) after it is working for a while. Any ideas?

Bill Putney (To reply by e-mail, replace the last letter of the alphabet in my address with the letter 'x')

Reply to
Bill Putney

Bill I never said it couldn't happen, I have seen switches, relays and sensors do some crazy things that just don't seem possible. But if I were to get such a complaint, I would have to start with using the scan tool to check inputs and outputs paying attention to the power, ground side of the switch. Clockspring and Circuit. And or connecting Co-pilot to the vehicle

Reply to
maxpower

I removed and cleaned the contacts on the brake switch and I haven't seen the problem since.

Thanks, all!

Reply to
PaulH

Reply to
maxpower

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