7-12 Bank Shut Down - 456 Cat Temp SDL Module | FerrariChat

7-12 Bank Shut Down - 456 Cat Temp SDL Module

Discussion in 'Technical Q&A' started by DrivenHK, May 2, 2019.

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  1. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    Am reaching out to community for help in diagnosing this one. Hopefully documentation will help others with similar issues.

    Friend purchased "As Is" and we don't have history on the car. '94 456GT, euro spec RHD 2.7Motronic (SDL for each bank), Manual Transmission. Have been tasked to help bring car back to road worthy condition.

    With Ignition 12V, the orange color bank 6-10 & 7-12 lights will turn on. Red SDL 6-10 is on but the 7-12 does not light up. (Have yet to check the bulb.) Once engine fires up, 3 aforementioned lights turn off.

    After a couple minutes idling; LH bank 7-12 shuts down. Disconnecting either the (LH) thermo-couple or the SDL module connector on the LHS will bring the LH Bank 7-12 to life. The 7-12 SDL does not illuminate at any time.

    When 7-12 shuts down, with a stethoscope can hear 1-6 injectors dial down but still firing.

    Tested continuity at LH therm-couple - no continuity. RH thermo-couple - resistance increases with engine temp.

    OK - All things point to bad thermo-couple and may be a missing 7-12 SDL bulb...

    To confirm - Swap Cat SDL Modules side to side: With expectation of no change, i.e. 7-12 shut down because of bad thermo-couple sensor. But...

    - All connectors plugged in, both banks run normally, no warning lights.
    - Unplug LH Cat SDL module connector, no change both banks run normally. 7-12 SDL remains dark/off.
    - Unplug RH Cat SDL module connector, 1-6 red SDL turns on solid, no change both banks run normally.
    - Unplug both LH & RH Cat SLD module connectors, 1-6 SDL is solid, no change both banks run normally.

    Swap back Cat SLD modules to original position and situation reverts to 7-12 shut down. Hopefully I am missing something simple and gurus can chime in. Thank you!

    Other Notes:
    All Cam/Crank speed sensors and Pre-Cat o2 sensors replaced. There's only 1 Post-Cat o2 sensor located on LH side exhaust (no bung on RH). Wires to post cat o2 have been cut. Have a new o2 sensor but yet to find the harness/plug. Suspect it's tucked away inside the under tray somewhere.
     
  2. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    Questions:
    • Is the bank supposed to be able to run with the SDL modules disconnected and SDL on solid?
    • Why would 7-12 continue running with the RH module swapped (connected to the bad LH thermo-couple)?
    • May be both the LH thermo-couple and RH SDL module are no longer working?
    Thank you!
     
  3. scowman

    scowman Formula 3

    Mar 25, 2014
    2,479
    Scottsdale AZ
    Full Name:
    Stu Boogie
    Ferraris are set up to be 2 six cylinder motors. So Swap Motronics. Does problems switch sides?
     
  4. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    Thanks for your reply.

    Did switch motronic ECU sides. No change.

    Thermocouples stayed in situ. Tried tests over several heat cycles.

    During one round of tests, was able to produce a repeatable condition where by both Cat SDL control module shut down bank 7-12 when thermocouple plugged in. That seems to suggest one intermittently performing Cat SDL control module.

    Am guessing switching the thermocouple would cause shut down to move from 7-12 to 1-6. Will be sourcing a new module and thermocouple as next step.

    Is there a primary/master secondary/slave relationship between the 2 motronics?
     
  5. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    1. Show me a picture of the Thermal Control Module. Black or green?
    2. Figure out the bulb issue and fix that.
    3. Get a laser thermometer that is good for 1000F and start measuring the temperature of the tail end of the cats and post what temperature that is
    4. Find four crimp-type splice and crimp the four signal/ground wires coming out of the control units so you can attach a DVM to see what voltage you are seeing
    a) do this in the engine bay if the problem shows up at idling
    b) do this at the main ECU connector in the cabin (I assume the main ECUs are in the cabin) if you want to see it in action while you are driving

    Answers to some of your questions: there should be no primary / slave relationship between the two 2.7 motronic other than they "may" share a single cam phase signal
    The older thermal control modules are susceptible to cracks and let in moisture which causes the SDL to come on and shut down the bank. While there are some cases of the actual thermal couple going bad, the ratio is 10:1 more control modules than thermal couple.
     
    DrivenHK and f355spider like this.
  6. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    Yelcab - Thank You.

    1. The housing is black. Image attached
    2. Not sorted this yet.
    3. Idle getting reading of 230C but not sure if this is accurate. there's a heat shield on the cat.
    4. (a)

    4 pin connector:
    Thick Orange/Thick Black/ Thin Pink / Thin Pink/Black

    LH Control Unit @ left bank - When 12 cylinders firing (thermocouple unplugged):
    Orange 14.23V
    Black -0.001V (Continuity to Ground)
    Pink 5.03V
    Pink/Blk 4.99V

    LH Control Unit @ left bank - When 6 cylinders firing (thermocouple PLUGGED):
    Orange 13.86V
    Black 0.00V (Continuity to Ground)
    Pink 4.54V
    Pink
    /Blk 4.99V

    RH Control Unit @ left bank - 12 cylinders firing(thermocouple unplugged):
    Orange 14.20V
    Black -0.001V (Continuity to Ground)
    Pink 5.36V
    Pink/Blk 4.99V

    RH Control Unit @ left bank - 12 cylinders firing(thermocouple plugged)::
    Orange 14.20V
    Black -0.001V (Continuity to Ground)
    Pink 4.87V
    Pink/Blk 4.99V

    Image Unavailable, Please Login Image Unavailable, Please Login
     
  7. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    OK, this is how the Slow Down Light module logic works.

    1) normally running, no issues
    2) Cat temperature reaching the first threshold T1, SDL will flash telling you that you have a problem
    3) Cat temperature reaching the second threshold T2, SDL will come on solid, again confirming to you that you have a serious problem
    and wanting you to slow down
    4) If you do not slow down and continue driving for x number of minutes, the ECU shuts off the ignition to that bank where the solid SDL is, it also throws a CEL code in OBD1/OBD2

    On Bosch 2.5 / 2.7, disconnecting the Thermal couple module or the thermal couple from the module lets the car run normally. On Bosch 5.2, either of those actions will cause the SDL light to come on solid immediately.

    What you seem to have is two things:

    a) the SDL light on bank 2 (7-12) is either burnt out, or removed by the previous owner because he did not want to see the light.
    b) the TC control module that was originally on bank 2 (7-12) is probably toast and putting out garbage voltage.

    There is a clue right here:

    LH Control Unit @ left bank - When 6 cylinders firing (thermocouple PLUGGED):
    Orange 13.86V

    That Orange wire is the battery voltage signal coming off the Alternator feeding the control module. It is 400mV lower than the other times which means the module is drawing excessive current to pull down that power line.

    If there is something I would do, it is to buy a new thermal couple controller unit and swap that out on bank 2. I know it is $500.

    There is a potential third issue, and that is one of the TC (the one that has infinite resistance) is actually bad in addition to the control unit. And that is why swapping the modules left to right does not give you any clue because … there is more than one point of failure.

    Good luck.
     
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  8. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    Thank you for this information. Yes something about the interaction between the bad TC and left side Control Unit is causing the condition. Have got a new TC and Control Unit on it's way. Will reinstate the bulb and report back after testing. Thanks again for your help.
     
  9. DrivenHK

    DrivenHK Rookie

    May 1, 2019
    28
    Hong Kong
    7-12 SDL Bulb Reinstated - Was in fact removed. Cycles on/off at ignition.
    Thermo-couple replaced LHS: Testing at idle, left control module is no longer shutting that bank down. 7-12 SDL light stays off.
    The open circuit Thermo-couple sensor tip was eroded, shorter than new probe by about half length.
     
    Qavion likes this.
  10. yelcab

    yelcab F1 World Champ
    Consultant

    Nov 29, 2001
    12,661
    San Carlos, CA
    Full Name:
    Mitchell Le
    Glad you solved it.
     

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