355 - Slow down light diagnosis and test to repair? | FerrariChat

355 Slow down light diagnosis and test to repair?

Discussion in '348/355' started by 355OXO, Feb 16, 2020.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, Skimlinks, and others.

  1. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    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
     
  2. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    11,484
    Sydney
    Full Name:
    Ian Riddell
    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).
     
  3. Drock28

    Drock28 Formula 3

    Jan 13, 2013
    1,429
    Montreal
    Full Name:
    Tony
    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)..
     
  4. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    Many thanks Simon
     
  5. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    Many thanks Simon
     
  6. Challenge

    Challenge Formula 3

    Sep 27, 2002
    1,933
    PA
    Full Name:
    Kevin
    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.
     
    308 GTB and Qavion like this.
  7. Drock28

    Drock28 Formula 3

    Jan 13, 2013
    1,429
    Montreal
    Full Name:
    Tony
    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..

     
    ernie and phrogs like this.
  8. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    Simon you need to tell us first if everything is stock,if not give the details.
     
  9. lanab

    lanab Formula Junior

    Feb 21, 2016
    442
    Stockholm, Sweden
    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....
     
  10. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    thank you that was really helpful and shows way to diagnose the problem.
     
  11. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    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.
     
  12. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    11,484
    Sydney
    Full Name:
    Ian Riddell
    Have you turned off the immobiliser and turned on the ignition?
     
    355OXO likes this.
  13. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    Yes i have done that, thanks.
     
  14. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    Qavion, thanks,
     
  15. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    11,484
    Sydney
    Full Name:
    Ian Riddell
    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)
     
    emac likes this.
  16. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    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
     
  17. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    Thanks for the input will check.
     
  18. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    11,484
    Sydney
    Full Name:
    Ian Riddell
    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.
     
    johnk... likes this.
  19. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    many thanks for the input
     
  20. 355OXO

    355OXO Karting

    Apr 16, 2006
    198
    UK
    Full Name:
    Simon
    thanks I will review this thread as it may help me
     
  21. WATSON

    WATSON Two Time F1 World Champ
    Owner Rossa Subscribed

    Sep 9, 2010
    21,613
    WI
    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.
     
    taz355 and emac like this.
  22. emac

    emac Formula Junior
    Silver Subscribed

    Sep 14, 2014
    851
    upstate SC
    Full Name:
    ernest
    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..
     
    Qavion likes this.
  23. taz355

    taz355 F1 Veteran
    Owner Silver Subscribed

    Feb 18, 2008
    5,942
    Indio Ca/ Alberta
    Full Name:
    Grant
    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.
     
    Qavion likes this.
  24. emac

    emac Formula Junior
    Silver Subscribed

    Sep 14, 2014
    851
    upstate SC
    Full Name:
    ernest
    my by pass and right side ecu connectors were swapped after a major
     
  25. Qavion

    Qavion F1 World Champ
    Silver Subscribed

    Feb 20, 2015
    11,484
    Sydney
    Full Name:
    Ian Riddell
    Does a swapped connector cause an SD light when the car is cold?
     

Share This Page