slow down light

There are many, many, many threads on this. Use the search function and you will find many, including some of mine. Mine finally went away when I put in a new cat ecu. Good luck

 

The slow down light in my 355 would go on in a seemingly random manner. If it was cold and raining and I was driving slow it would alert, if it was warm and dry and I was driving quickly no light. Dealer diagnosed the problem as cat ecus. Fixed it. No more light.

David

 

Generally it will be either a bad ECU (there are three on the 96 to 99 cars) or a bad connector to the ECU. Easiest way to find the fault is with an SD2 diagnostic tool (dealer item).

Assuming only one is bad, you could buy an ECU and start swapping positions until the light keeps coming up. BUT, what if you have more than one bad, or have a bad connector? Then diagnosing becomes more complicated.

 

Hi Mac,

Please fill out your profile with your name, location, etc. so that the community can get to know you. You may find that people will be more willing to help a member who has taken the time to introduce himself.

Although I recommend that you do a search, I will try to give you some additional useful information. There was just a recent thread on this not too long ago.

There are two possibilities for why your Slow-Down light is coming on:

1) The system is performing as it should.
2) The system is NOT performing as it should.

If the system IS performing as it should, then you have a critical problem. I hope that you have read your Owner's Manual and have investigated the meaning of the Slow-Down light. It means that the temperature of the catalytic converter is too high. A catalytic converter overheating can first be bad, next be disastrous, and last be a colossal catastrophe for your engine.

If the system is NOT working as it should, then that means the Slow-Down light was not supposed to come on. For example, if the Slow-Down light comes on shortly after you start the engine (I mean after it comes on initially during the diagnostic check when the ignition turns on), then you know that the system is malfunctioning because it is not possible for a catalyzer to overheat in just a few seconds or even just a few minutes after cold start.

There are several reasons, as stated in this thread by others, as to why the system could be malfunctioning: you could have a bad thermocouple or a bad thermocouple control module (a.k.a. catalyzer ECU a.k.a. exhaust ECU); or, quite simply, the connection(s) in the system could be bad and just need cleaning.

Are you running the original catalytic converters? If so, I recommend changing them regardless of whether your Slow-Down light is coming on for proper reasons. Original Ferrari catalyzers are ticking time bombs that will fail eventually and cause this problem -- it is just a matter of time. At the very least, you should have your catalyzers analyzed by your mechanic to see if they are sound. This is done is a few ways: for example, he can listen with a scope; he can also test your exhaust gases AFTER the catalyzers to see if the catalyzers are doing their job. If the numbers are off, then we know your catalyzers are bad.

If we assume for the moment that the Slow-Down system is functioning properly, then another possibility is that your engine is running rich, thereby causing the catalyzers to overheat. You really should make sure the engine is NOT running rich. The way to do this is to have a 4-gas analysis done on the exhaust gases BEFORE the catalyzers. There are ports on the exhaust manifolds for this purpose. The idea is this: the engine should run fine on its own without the help of the oxygen sensors -- that is, the oxygen sensors exist only to make minor adjustments to the fuel mixture; they are not supposed to make major corrections to a fuel mixture that is way off to begin with. The results of the 4-gas test BEFORE the catalyzers should be within specific parameters.

 

If the car is OBDII (motronic 5.2 on 1996 to 1999 355's), the post cat O2 sensor should also detect low cat efficiency and trip the "check engine" light. Been there, done that.