99 355F1 with flashing slow down light

With the 99 355's, running the 5.2 Motronic, it's a bit harder to nail down which cat ecu is giving you the problem, by yourself, because you only have one slow down light. But, that doesn't mean it can't be done.

Run a search of the archives as this has been talked about extensively, and you find plenty of info. Same deal for the codes.

 

Yes. There is a plug that goes into the SDECU. You have 2 of them. The plug has 3 wires ground, 12V, and output trigger 1/2-5V going to the motronic ECU. The smaller 2pin plug is from the thermocouple on the cats. Use a VOM to find the trigger wire on each SDECU. Then wire in a simple 1.5V battery to each SDECU and your light should go off. Then use just 1 1.5V battery on one of the SDECUs to figure out which side is giving the fault. Lets say you find the passenger side SDECU system is faulty. Then you can swap SDECUs left to right to find out if the problem travels. If problem travels you likely have a bad SDECU. If problem stays on that side you likely have a bad thermocouple. Watch for my future threads on this and I'll tell you how to delete this important but wonky Ferrari system and add in a EGT which will give you more information and not break down.

 

Ooooooo man.
Good looking out chubbalard.
That is a pretty crafty way to figure it out. Big time Stooge points for that one.

 

wait a minute, have you been driving my car??? that could be my post...'99 355F1, slow down light on occasion at start up....I'm reasonably sure it's a cat ECU based on how random it comes on and goes off, especially when the car is stone cold. But do need to fix it soon, emissions is due in a month or so.

 

Hold on now...how is he going to do that, when he is throwing codes for all THREE ECUs? Did you notice the three DTCs he listed? 1445, 1448 and 1449. That is for bank 1, center bypass exhaust valve and bank 2.

I would recommend looking at all three of his catalyst ECUs to start. If they have the black epoxy potting which identifies them as the original first generation ECUs (which commonly fail), then he should start by replacing all three with the later green ones. Or in the alternative, he could buy just one or two, and move them around and see if it kills the code for that area. But serious, if they are the old style, he should simply replace them all. It will likely fix the problem and even if it does not eliminate all the codes, it will certainly fix one or two of them, AND it eliminates it from consideration in the future.

 

Sure you can do it by replacing parts or you could diagnose the problem. I'm too poor to throw parts at my car.

 

And I would silicone the new ones before putting them on. When I first got my 355, I replaced one ECU with a newer version green one. Within a year it had started to crack around the edges. Little black silicone can't hurt to help keep the dirt and water out of them over time...

 

Silly question, but I am chasing a similar issue with the same codes.

Bank 1 = Drivers side; Bank 2 = Passenger side?
- or -
vice versa?

 

I did the same thing. I put some black silicone around my new green ones before installation. A worthy 2 minute precautionary measure.


Also...

P1445 - Passanger Side Cat ECU
P1448 - Bypass Cat ECU
P1449 - Driver Side Cat ECU

You will also throw a P1448 code if your bypass valve is wired open. Be sure it's not wired open before replacing that ECU. The other 2 surely need replacing.

 

Excellent. Thank you.

I just got the green ECU , all 4 new O2 sensors and a thermocouple to swap in and try. The bypass valve is not wired open though I considered it.

Not to hijack the thread, but is there a way to test the by-pass valve for proper operation so I can move off of that and onto something else like the solenoid valve?

 

My point is he has codes for all three catalyst ECUs being bad....that makes swapping them around a useless exercise. Also, the old style black catalyst ecus have been so trouble prone and a headache, that is why Ferrari came up with the better quality green ones. If the OP finds that only one or two are actually bad, and not all three, I believe it is saving him time and trouble not to have to deal with this again in 4 months by just replacing them all now.

 

It is not on the available lists for Ferrari that are open source. A google search seems to show that for most car makers, this is related to a problem with sensing the wheel or vehicle speed. The speedometer/odometer is not disconnected or malfunctioning is it?

 

Typical! That is why you need a proper diagnosis. I gave you clues to how the system works. Now you go play with it to figure out exactly what your system is doing. The ghosts you experience that have not come back yet are typical ferrari. You can't believe the ghosts but you can chase them and use them as a starting point. "Note them but prove them" otherwise you spend lots of money on parts you don't need. There in lies the reason I'm so high on Dave's SRI inovations gold connector kit. It is not just the gold it is the system that makes it work. Just swaping some cheesy pins is not going to do it. You have to have a properly functioning car before you can hunt down ghosts and that is why just because there are 3 codes does not mean swaping around ecus and thermo couples or sending 1.5V to the ECU trigger is a bad idea. It is part of the vetting out and figuring out of how our systems work because we diy'er's don't have the proper diagnostic tools or the factory training. Even then these boards are full of stories about real mechanics with SD2/3 still swapping parts to fix a car and unsuccessfully at that. IMO it is because the cars are not running right to begin with because of the crap connectors ferraris come with. There are stories right here on Fchat about how some of our resident pros had problems with ghost chasing at delivery at the dealerships! Everything starts with a properly running car. DaveHelms has the answer. Some people are starting to listen.