348 Tb... My 'one day, one problem' thread.

Did you recently replace both engine ECUs? I'd start there. Careful, the connectors' contacts aren't as firm as they used to be (in other words, spring tension).

 

Darn, sorry. I was thinking about the Check Engine light, which does get its signal from the ECUs.

According to the wiring diagram I'm looking at, Slow-down light (1-4), item number 128, the VR wire (green/red) goes from the bulb, through connector 126 and the passenger footwell fuse box, and onward to the Exhaust System Temperature ECU.

 

The SDL bulb is lit up by the exhaust control station ("SDECU") for about 1 sec. at ignition switch on. Your SDECU for 1-4 may be bad so try with swapping the SDECU-s to diagnose. You can also check whether you have code 4121 in the 1-4 engine ECU.

 

...or if you haven't re-installed your instrument binnacle, you could check the resistance of the wiring between the right hand instrument plug (pin 9, green/red wire) and the 1~4 SDECU plug (pin "B").

I don't know if the wire colours are visible at the SDECU plug, but pin B may have a green-red wire.

I'm assuming you have a 6-pin plug on your SDECU.

 

Should this code normally generate a Check Eng light, Miro? If it does, perhaps Marc's problem is simply a Slow Down lamp circuit (?).

It may depend on what is broken inside the SDECU.

 

In my case, non-cat UK model, I just find the ECU code stored for the bad SDECU side. No CEL or any engine running problem. I currently have both SDECU-s disconnected and no issues at all.

 

I'm confused. Isn't the 1~4 light on the right side of the instrument binnacle? Thus, the right side ECU was inoperative. If you swapped ECUs, the left side light (5~8) and ECU should now be inoperative. Do you understand the engine cylinder numbering on Ferraris?

ECUs are surprisingly expensive... over U$500 plus postage

 

I think it's just the beginning of finding a solution. I presume your SDECU-s are the type with two and six pin connectors, filled with black resin. Buying another unit of this type (if you can find it) is a waste of money as they don't last. The alternatives are:

1. Just disconnect the bad SDECU (or both) if this does not cause any CEL-s (it will not if your car is a non-cat Euro). However, you will not get any "too hot exhaust" warning.

2. You can buy much cheaper 355 SDECU-s (green resin) and adapt them for use on the 348 (see posts at "348 SDECU pinout/wiring diagram" hanging around at the moment).

3. You can install aftermarket EGT gauges to continuously monitor the exhaust temperatures

4. You can build your own SDECU - 100 times linear voltage amplifier with a circuit which will switch a relay on at 3.75 volt coming out of the amplifier to light the SDL and, if you also want bank shut down, another circuit to switch another relay on at 3.9 volt from the amplifier.