"Slow Down" light ON during cold startup | FerrariChat

"Slow Down" light ON during cold startup

Discussion in 'Mondial' started by djs308, Feb 8, 2015.

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  1. djs308

    djs308 Formula 3
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    Sep 2, 2002
    1,100
    Long Island, NY
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    David S.
    Just got my 3.2 coupe back from an engine out major. Car is running nicely! Too bad it’s going to stay in the garage because of all the snow/ice we’ve had in New York lately.

    However—

    In the last year (basically since I bought it), I’ve had an intermittent issue with my “Slow Down” light flickering at random times, and occasionally staying on for extended periods of time.

    The previous owner ran straight pipes so he never had this issue. I had the original cat put back on the car when I got it. At the time, I was not sure of the emissions requirements here. Had my mechanic check it out. He said that the cat probably was shot (original part). Ordered and installed a HyperFlow. Also changed out the O2 sensor. Car ran well.

    Still, the issue persisted. But again, it always has been a random occurrence. I’ve checked the temps – all have been normal. Cat was not overheating. Mechanic checked it again. Now we’re thinking it’s the thermocouple. He checked the contacts and cleaned them. The issue seemed to go away for weeks, and then came back. But again, intermittently.

    So now, I drove the car home from the major and the light was on full bright, immediately from start up. It stayed on. The car was stone cold when I started it. Clearly not an overheating cat. The mechanic had checked the thermocouple wires again and even made sure to secure it so it wouldn’t be loose, and incidentally contacting the cat while underway. I’m going to run it again and see if it repeats that consistently.

    I have searched and seen a number of threads on this, but I am not mechanically inclined and do not know how to properly troubleshoot this. It could be a bad thermocouple, ECU, relay, fusebox board, etc.

    Thermocouples are unbelievably expensive (IMO) so I’d like to rule everything else out before biting the bullet and replacing mine. I would also prefer to resolve this issue properly, rather than disconnecting the thermocouple altogether, which merely masks the underlying issue.

    There are only two other electrical issues that I know of: 1) my driver’s side door lock switch doesn’t work, and 2) my glove box door switch was intermittent, and now no longer works either. (Bad switches)? Probably not related to the thermocouple issue, but just wanted to mention those anyway.

    Any advice for this (still) Mondial newbie would be greatly appreciated. Also, any leads on a reasonably priced thermocouple would also help!
     
  2. Wade

    Wade Three Time F1 World Champ
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    Mar 31, 2006
    32,793
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    Wade O.
    #2 Wade, Feb 8, 2015
    Last edited: Feb 8, 2015
    Hello David,

    Unfortunately, there's loads of info but no easy solution without some clear troubleshooting. Have you searched the 308/328 forum as well? Also look at the Tech Q&A forum. Lots of good reading (i.e. learning) in both of those forums.

    Use the search keywords: Slow Down and, separately: 328 thermocouple

    As a reminder, the Mondial t is entirely different
     
  3. djs308

    djs308 Formula 3
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    Hi Wade. Thanks. I have checked through there but much of the info is well above my head.

    I guess the biggest question I'm trying to figure out is whether a thermocouple can be "restored" or whether it's the kind of part that once it's toast, it has to be replaced. Contacts were cleaned and the wire itself was wrapped with thermal tape. I just don't know enough yet to understand how the thermocouple actually works and whether it's a repairable part. But I'll take another look through the 328 section for any new info.
     
  4. djs308

    djs308 Formula 3
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    #4 djs308, Feb 8, 2015
    Last edited: Feb 8, 2015
    I just found a "used" thermocouple on ebay for a more reasonable $300. Any consensus whether getting a good used thermocouple is just as good as buying new at almost double that cost? Also found a NOS for $500 at Algar. Oh wow, Ricambi's price came down by almost 50% since I last checked there! Hmmm... so many choices...
     
  5. mulo rampante

    mulo rampante Formula Junior

    May 31, 2011
    997
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    Charles
    Hi David:

    I think you need to make a determination that the thermocouple is indeed bad before investing that kind of money.

    I've never had an issue with mine, and I've never opened up my control units. I also have an older and therefore different car -- but I have used thermocouples in my work for years.

    A few thoughts:

    Swapping the leads between the two banks would allow you to identify whether the problem is associated with a thermocouple and its associated wiring. (i.e. if it moves to light the other slow down light when you do this.) Sorry, if I had the same car as you I could give more precise info, but I think they are somewhat different.

    If one of the wires should short to the chassis I think you could get these indications. If it is intermittent, it sounds like a faulty connection that works sometimes, or an occasional short to the chassis. Understood the tech has gone through the thermocouple wiring and you have some confidence in it.

    Most of what I recall reading suggests that the most common problems with these are degraded wiring due to rubbing, etc. or the catalytic control unit "CCU" failing.

    Thermocouples themselves are very simple, just two dissimilar metals joined together -- they produce a (very small) voltage in response to temperature. They also tend to either work or not work, since they rely on the fundamental physical properties of materials in their operation. I'm pretty sure ours are type K, which use alloys called chromel and alumel.

    I've bought a lot of stuff from Omega Engineering in Stamford over the years. They're a big player in industrial temperature measurement. Chances are you could find a suitable replacement in their catalogue.

    Explanation of thermocouples: thermocouples and thermocouple probes

    Thermocouple selection guide: Thermocouples

    Finding a part might be pretty daunting if you're not accustomed to this... if you decide you need a new one and you can get me some mechanical dimensions on the thermocouple probe, I'll see what I can find. If a suitable replacement can be found in the industrial world, it would be very inexpensive.

    I'd check the other connections at the CCU and make sure everything is intact.

    Hope to see you at the Concorso again this year.
    Charles

    EDIT: I would have no qualms about buying a used one if the seller offers some kind of guarantee.
     
  6. Wade

    Wade Three Time F1 World Champ
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    That's my experience too Charles; not convinced that the thermocouples are the problems.

    Excellent info in your post as well.
     
  7. PV Dirk

    PV Dirk F1 Veteran

    Jul 26, 2009
    5,401
    Ahwatukee, AZ
    I fiddled with mine for a few years off and on. I know it's not a cat issue so in the end I disconnected it. Didn't like it flashing in my eyes on dark nights. It appears that it was a poor design prone to failure from the beginning and IIRC some who spent the money to fix it had the problem come back ultimately.

    Sorry I have no good info, this is just what I ended up doing.
     
  8. djs308

    djs308 Formula 3
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    Thanks for the assistance guys. I'm going to do some more poking around in the car. I will recheck the connection at the ECU in the trunk. I know replacement ECUs aren't inexpensive either!

    While I do believe it is 100% a "false alarm" signal as far as it not being related to overheating, I still would like to somehow track down what has been causing it.

    Charles, I think my 3.2 is a little different than your QV in that mine only has a single SLD on the dash. As I don't have a lift at home, I also don't think I could properly test the TC myself. It's possible mine has finally shorted out completely, but a visual inspection didn't seem to show anything glaringly obvious. Is it possible that the wires inside somehow got corroded enough to fail completely?

    My mechanic said he would put a call in for me this week with a Ferrari-factory technician he is acquainted with to get some further insight.

    Yeah, I'm a bit leery of throwing big bucks at this before knowing with confidence what parts are bad.

    I'll do some more reading on this, thanks again.
     
  9. mulo rampante

    mulo rampante Formula Junior

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    I agree that it's a false alarm.

    If the wires were corroded inside the jacket, I don't think this would matter, unless one had completely broken. The thermocouple wires are of the same material as the thermocouple, if they shorted together, I think you'd have a second, and I suspect rather poor, thermocouple junction where they touched. I think this would decrease the likelihood of the lamp illuminating. If one of the wires were to have a break, then it's anyone's guess as to what might happen as I think the result depends upon the connected circuit.

    I thought there were some differences between out cars, one slow-down light does make it harder to diagnose without equipment. I'm assuming that you still have two thermocouples.

    Some other tests: A resistance reading on the thermocouple leads with them disconnected from the CCU should indicate something close to a short circuit, just a few ohms at most. So you could do this as a continuity test.

    You could also measure the resistance from each wire to the chassis of the car, and see if the two wires of the thermocouples measure similarly to one another. I have no idea what the expected outcome is in this latter test (depends on the circuit), but if you saw that one thermocouple that indicated very high resistance to ground while the other didn't, this might point out a potential problem.

    If you suspect an intermittent short or open you could try moving the wires around while taking a reading and looking for changes. A meter with a continuity test mode that beeps is good for this.

    Measuring the actual output voltage of the thermocouple with a handheld multimeter is probably not going to tell you much. There are other instruments that are better for this.

    Anyway, just a few thoughts.
     
  10. djs308

    djs308 Formula 3
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    Very interesting info, Charles. If I understood correctly, a short inside would cause the TC to fail in a way that would NOT light up the SDL? If so, what condition would need to be present to cause the light to turn ON?

    Unless it really is more likely an issue with the ECU/board in the trunk?

    Also, my 3.2 has one cat, one SDL and only one thermocouple. I suppose that's both good and bad.

    One other theory – is it possible that moisture might have been getting in somehow and intermittently shorting the system out? My mechanic did wash the car before I picked it up. He said he never saw the light on when he road tested it earlier in the day. Only when I got in to leave did it pop on.
     
  11. mulo rampante

    mulo rampante Formula Junior

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    David: If the two leads going to the thermocouple were shorted together, I would expect less voltage to be seen by the CCU, and this would correspond to a lower temperature indication -- hence, no light. There are a couple of other fault conditions I can speculate about:

    If it was an open circuit (i.e. a break in the wiring anywhere between the thermocouple and the CCU), it's harder to say what would happen. If I had a schematic for the CCU I could make a better assessment of that. I think it could go either way for a number of technical reasons that are beyond the scope of this post!

    There's also the issue of one of the thermocouple leads shorting to chassis ground: You might think that this should result in no indication, as the thermocouple's output voltage wouldn't be seen by the CCU -- and this might be the case. It is also possible that the ground potential of the circuit that reads the thermocouple might be different than chassis ground, and the difference would register as a voltage, perhaps giving a false high temp. indication. This is due to current flowing between the two grounds through the small but non-zero resistance of the wire, it gives rise to a voltage that could be sensed by the CCU. (Zero ground potential is a theoretical thing: All wiring, connectors and car chassis have non-zero resistance, and if any current is flowing between different points, it will give rise to a voltage difference between those points. The same can be said for any wiring in general. The point here is that 'ground', just like the positive battery voltage, may not be the same all over your car.)

    Thermocouples produce very small voltages, for a type K thermocouple the difference in the voltage it produces at room temperature and 500 degrees C is only about 20 millivolts... cars are electrically 'noisy' environments, so there are a lot of things that could upset the reading if there's a circuit fault. And it doesn't take a lot of electrical resistance for a 20 mV difference to arise somewhere in a circuit.

    I'm not saying that either of these things is happening here, but I've seen problems like this in other systems that use thermocouples.

    Well, this is possible, but we're just speculating without measurements or physical evidence of a problem. When troubleshooting these things it is important to bear in mind that most electrical faults occur where something mechanical is going on, e.g. a wire rubbing, or a poorly-mated contact. Wires seldom fail, connectors fail all the time :)

    Yes. I wasn't aware that they had gone to one cat. One nice feature of having two is you can get a good indication of which side may be running poorly due to fuel or spark problems. And, of course, it allows some things to be swapped around for diagnosis. But no matter, really.

    Entirely possible. We've both seen some of the crazy stuff that's been reported here due to moisture getting in the electrical system. The PO of my car had a bad CCU module and IIRC it was due to moisture.

    One other thing is that you might want to check out the wiring to the CCU, particularly the power and grounding wires... this should be in the wiring diagrams book, and might get a mention in the workshop manual (not sure).

    Given the fact that the car was recently washed, I absolutely wouldn't rule out a moisture issue. If you have a heated garage you could put the car in for a few days, it would help to answer this possibility. Removing connectors, drying them out with a contact cleaner that leaves no residue ("tuner lube" is good, so-called because it was originally meant for analog TV tuners), and reinserting them might be of some use.

    Sorry... a rather lengthy reply. A few of the things I've touched upon I probably haven't adequately explained either -- hopefully it's clear. Bottom line is I'd focus in visual inspection, removing, possibly cleaning, and re-seating connectors, and looking for potential moisture problems. The latter might just be a bit of a waiting game. If the problem still persists we can look into some electrical measurements.
     
  12. soucorp

    soucorp F1 Rookie

    Sep 20, 2011
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    REF: There are only two other electrical issues that I know of: 1) my driver’s side door lock switch doesn’t work, and 2) my glove box door switch was intermittent, and now no longer works either. (Bad switches)? Probably not related to the thermocouple issue, but just wanted to mention those anyway.
    ~~~~~~~~~~~~~~~~~~~~~~~~

    Hi,
    Just for the record, your thermocouple has nothing to do with your door lock/glove box switches not working. Sounds like something is causing the fault, either loose connection, bad wire, or its rubbing against the cat or exhaust. Mine acted up a few years ago and freaked me out. No over heating cat, just a bad thermocouple wire that was grinding on the edge of the cat right to the bone causing a false light of 'slow down'.

    I traced the wire, removed the prob end from the cat, used thermo tape to wrap the exposed wire, made sure other end was plugged into the ecu securely, put everything back on and that seem to have fixed the problem. Also, I have noticed in down pouring rain, it wreaks havoc on the system and all kind of things can light up so don't test it in the rain.

    Best,
    Mike
     
  13. jgoodman

    jgoodman F1 Rookie
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    Mike press on the door while you press the glove box switch and it just might open.
     
  14. soucorp

    soucorp F1 Rookie

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    Hi Jay, I think you meant David, my glove box opens just fine.

    Cheers
     
  15. Faber

    Faber Formula Junior

    May 5, 2011
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    Tom G.
    Same issues as original post & pushing the glove door & switch fixed that issue - Intermittent Slow down lights on mine - cleaned & wrapped thermocouple per Soucorp suggestion but light came back after a day - got a used thermocouple from GT Car Parts - yet to install it but need to in case that fixes the issue - kink/wear in my original near where it enters fender well - mech. thinks it's ECU - we'll see - Cats never glowed so I can live with it for now -
     

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