Hi guys, I know there are many threads on this subject and it is a known problem with 355. My slow down light is flashing when cold. I have a 5.2 with 2 ecus that i have replaced. Should i replace the Thermocouple on both cats next and if that is not the fix then the Lamba sensors? I have disconnected battery power lead to reset warning light without success, is there a way of resetting this? What I really need is a step by step diagnostic and test process to resolve this issue. Any help appreciated. Regards Simon
You just need an OBDII (OBD2) reader to reset the light. It should also tell you which side is causing the light to come on (so you don't have to buy two thermocouples). Even the cheapest OBD2 reader should do this. Do UK cars have OBD2 ports under the dash? If not, you'll need a Fiat 3 pin adaptor to plug directly into your Motronics ECU behind the right hand seat. Lambda sensors have nothing to do with slow down lights (at least not on cold cars).
a flashing SDL at cold start.. is usually a dead exhaust ecu.. not usually the thermo probe, but yes could be possible. since you replace two ecu's. whats your exhaust setup..? stock cats or straight pipes.. given straight pipes can trigger intermittent flashing SDL.. depending on driving conditions ( slow traffic)..
I had the same situation a couple of years ago. Removed and cleaned the thermocouple-to-ECU connectors with electrical cleaner and problem has been gone ever since. Cover these up with plastic before washing your 355.
actually ironically.. just came across this vendor for Cat ecu and thermo probe replacements.. https://technistrada.com/ after watching this vid from Ratarossa.. cant believe I paid close to $1000 for two cat ecu about 6 years ago.. for basically a scare plastic box with a chip board inside... ridiculous..
Yes i found two revised green ECUs for cheap money from a scraped 360 and also changed the O2 sensors and thermocouples, problem gone now, had problem with slow down light on bank 1-4. Also binned the original crappy exhaust system where the bafflers were loose inside with Nouvalari 200-cell high flow cats and system....
Apologies for the delay in responding. I am running a Tubi exhaust with by-pass pipes, it is a 5.2 355 1997. Slow down light worked originally with this system Slow down light is flashing from cold Slow down light when the engine is hot is putting engine into safe mode I have a OB11 scanner with a 3 pin connector/converter as uk cars are 3 pin but i can't get a reading from the diagnostic port behind the passenger seat It had 2 new ECUs about 12 months ago and i have done 3000 miles on these Any help appreciated.
Strange. Does your OBD2 reader offer a range of different cars. If so, have you tried different ones (Sorry if I've asked this before). Mine didn't have Ferrari, but I recall it worked with Audi or BMW. Although you've recently replaced your thermocouple ECUs, perhaps you could try simulating the output of an ECU with a battery as Ratarossa did in his video for faultfinding purposes (noting the potential risks). It can also be simulated with a diode and a resistor as per wbt's 'no cat' fix... https://www.ferrarichat.com/forum/threads/simple-2-7-slow-down-ecu-replacement-only-for-no-cats.538719/ wbt went on to professionally manufacture cheap Ferrari ECU and thermocouples (Technistrada)
I would check all the components first, thermocouples, and exhaust ecu’s. Interchange them so the system will log where it’s getting the fault. If all components are good then it’s likely wiring and or connections. If the light is on when starting my understanding is it would have nothing to do with the bypass thermo because it’s not in use at that time. Re review bobs postss on the system they go through the whole system analytically and once you understand it you should be able to find the problem. If it turns on right away it’s likely connections or wiring as said above. I can not confirm but your ecu’s and connections must also be checked
A long message thread on thermocouple ECUs here: https://www.ferrarichat.com/forum/posts/145930782/ As in the video 2 posts above, you can help isolate the problem using a 1.5 volt battery. If that doesn't work, you have an Motronics ECU problem or thermocouple ECU-to -Motronics ECU wiring problem.
Make sure you have the right thermo couple plugged into the proper ECU. Swapped by-pass versus R/H cat ECU can cause your symptom. It did for my car anyway.
Ian, Thanks for posting that video. It puts the whole system into perspective for people trying to understand what is going on with the system . When I forst got my car and had issues, Dr Bob was kind enough to hold my hand until I understood what was going on..
Yes excellent point and often the cause, this is easily done by accident. Also you can not always be sure the previous owner plunged the harness from the main ecu’s (Behind pass seat)into the correct exhaust ecu’s (Behind pass rear tire) What I am trying to say is you can not assume the exhaust ecu’s for each main pipe and bypass are still in their oem position.