Slow Down 7-12

I had exactly the same problem with my 456, and after a particularly long continental autoroute trip the slow-down light was coming on every 100 miles or so and would reset after a short stop. Like yours, the car would also occasionally run very rough for a couple of minutes on start-up.

The cause was rich running, which was overheating the cats on the motorway and was also leaving a notieable black soot around the bodywork where the tailpipes exit. Having researched the cost of lamda-probe or MAF replacement, I spent 20 minutes cleaning the connections to the two MAF connected to the airboxes, and the problem went away immediately!

Hope this helps

Graham

 

I don't think your tip can be overemphasized. I had a check engine 1-6 light that was on essentially all of the time. I cleaned out every electrical contact I could get my hands on with contact cleaner, reset the computer as indicated in the manual (disconnect battery for a while then restart and let idle) and the light went away. Cleaning those electrical contacts should be the first remedial step anytime one of these lights comes on I think. If that fails then did deeper.

Alberto

 

Run a search for "slow down light" and you'll get a ton of threads.

I don't own, nor have I work on a 456, but this is a very common problem with 348's, which I own, and have worked on. The usual reason for the slow down lights in the 348's is a faulty catalytic converter temperature ecu. The easiest way we find out if it is a bad cat ecu is to swap the ecu's from one bank to the other. If the light/problem jumps sides then you know that the cat ecu is bunk. The other problem that occasionally pops up is a bad thermocouple. You can try the same test by swapping the thermocouples from side to side.

Try that and see if it works.

 

I wish i had known about the website for the sensors before. I remember paying a lot more for a set when i needed them a few years back.

Any chance of some pictures of the sensors you cleaned? Even a pic showing arrows pointing will be good. I can then add it to the site.

Thanks.

 

ARE YOU KIDDING ME?!

That is a total rip off!!! On my 348 it's takes 5 minutes to swap out the cat ecu. There are only 2 nuts holding it in place. I can't believe that they charged a hours labor to for a job the take only a few minutes. IN-FRICKEN-CREDIBLE!!!!!

Since the GBP to USD is a "buy on get one free" deal for you right now, give Ricambi a call. They will have what you need, and you can get it at half price. http://www.ricambiamerica.com/

 

I just looked on the parts manual for your car and there is only ONE nut holding your cat ecu in place. So these crooks charges you 140 quid to remove 1 bloody nut!!! Ridiculous.

 

Shocking!

 

Actually it's typical.

 

Might try having a tech see if there is an intake manifold leak. I was told by FofSF that my rough idle is due to leak on just the one side [my case 7-12]. This leak causes sensors to go haywire during first starts. IF I start after a long rest then same problem, but if I start after a short rest, say, filling gas or < 30 min. the startup has no probs.

this can cause on certain runs to have possible sensor troubles too.

I would have, before going off on replacing the sensors etc., to first do a check on such to make sure you are getting the correct mix.

I don't know of a means to test this on one's own: I DO agree that swap of ECU's will give some comfort, but might not truly solve the long term or ALL issues, just a possible ECU.

THE OBD I plugings under the hand rest of that side of the car, might help, but I don't have that ability, I let the tech handle it.

BTW< FofSF says not a big issue at this moment, but will, some future date, be an item to correct.

 

#42

 

Did the light come on after you swapped the cat ecu's from one side to the other? Or have you even done that yet? If you haven't, swap the cat ecu's from one side to the other and see if the problem jumps sides. If the ecu is bad then you should get the slow down light on the 1/6 bank. Try it and see what happens.

 

I had this same issue with my 456. Slow down light was always intermittently illuminating on one side only. I cleaned the contacts with no success. I used a thermocouple meter to measure the cat. temperatures when the light went on and both sides measured the same - and within spec. I swapped the cat ecu's from side-to-side to see it the problem would follow the ecu - and the problem went away. After several hundred miles of driving and a couple of months, the problem has not returned. (I did not do an A-B-A and swap them back to see if I could get the problem to return. Though this is good engineering practice, I did not want to push my luck!)

I hope his helps,
Mark

 

don't think that would push your luck. Should swap back to see if it comes back. Those lights DO serve a purpose....yes, the better cat seems to be handling the problem, and perhaps the original cat is marginal at such, but you may not be handling the issue.

should get it checked out....not sure of this but the OBD I connects are in each of your front, arm rests.

 

OBD I for 95 456 is on the left foot well, behind the carpeted cover on the left.

 

ok, will look. I was told in each arm rest, as there are two.

Haven't had a reason to use them on my own BTW.

 

Well coincidentally, I had the 1-6 light come on today again. This is the third time since I got the car. If memory serves, each time it occurred when the fuel level was very low, just before the fuel low light comes on. I wonder if I have a fuel delivery issue that manifests itself when the car is low on fuel weak fuel pump, fuel pick up not in the proper setting, etc. I'm going to have to start filling the car up when it hits about half a tank from now on and see if that keeps the light from coming back on.

Anyone else experience the light coming on under low fuel conditions?

Alberto

 

I am not a good resource in that I've not had the lights come on. BUT I have run into a low fuel situation a number of times...to the point of even coasting on the first drive I took it...seems all is well on the gague until you get to the last 1/4 level mark.....then it drops off drastically. No, matter. What I am saying is I have run into a low fuel situation numerous times and no trigger to the lights. I have only recently, been fueling with premium [last two fillups, and now keep a full tank in garage] so, I guess I somewhat dispell your concerns. Low octane, low fuel running, no lights.

Seems it might be time to check the mixture....seems too rich[?]...ever notice a fuel smell from the exhaust?, or would that be cat lights only?

 

Rik:

Thanks for the reply. Just got back from 14 days in Italy, so I just got it.

Thanks.

 

It's really just a thermocouple "amplifier" which boosts the millivolt signal up to a 0-5v range. I had posted its output on here awhile back, but here it is again:
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