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348 - Check Engine light - ECU code 4121

Discussion in 'Technical Q&A' started by goyal99, Jun 22, 2004.

  1. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    I have the following situation on a 1993 348tb I'm trying to diagnose:

    - car has NO cats
    - disconnected exhaust ECUs
    - brand new NGK Iridium plugs
    - replaced both O2 sensors with newer used ones (see photos)
    - car is running well with slightly "rich" mixture (old plugs were darker on bank 5-8 when removed)
    - Check engine light 5-8 bank comes on and stays ON all the time after start up. Bank 1-4 light goes off a few seconds after start up (normal mode).
    - the ECU reading shows code "4121" on BOTH ECUs but only the 5-8 bank has the "Check Engine" light on (very strange)....

    The ECU code "4121" is in reference of Catalyzer Temperature ECU, which in my case is bull crap because both my temp. ECU are disconnected and I'm running without cats....So there shouldn't be a temperature issue at all...I'm wondering if there's a running issue that the ECU code is masking.

    Does anyone know how to correct the "4121" ECU code??? It may not be a real problem at the moment because the car appears to be running well but it's annoying to have to stare at the idiot light on the dash...BTW, I have reset the ECUs several times (by disconnecting the battery) but I still get the same code at start up.

    Suggestions welcome - VK
     
  2. ernie

    ernie Two Time F1 World Champ
    Lifetime Rossa Owner

    Nov 19, 2001
    22,022
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    I have the same code on my car. I was told that even though the exhaust ecu is disconnected and the engine will run, the Motorinic will give that code if it isn't getting the signal from the exhaust ecu. Have you tried to clear all the codes that are in the Motronic? It isn't the same as resetting the the ecu. After you pull the code/s there is another set to clear them out. It could be that you still have old codes stored in the ecu. I think after you pull the code/s you have to push the button one more time to stop the codes, then I think you have to hold down the button for at least 10 full seconds to clear them out. I'm not for absolute sure on that so check the manual on how to clear them for sure.
     
  3. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
    19,262
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    Why are you guys disconnecting the exhaust ECUs? I realize that they are not actually needed from a functional "is-my-car-on-fire" viewpoint if you are cat-less, but I don't see the harm in leaving them in place (and as ernie said there is an intelligent connection between the injection ECU and the exhaust ECUs so why mislead the injection ECU?). If the test pipe doesn't have a location for the thermocouple why not just tie it up in a safe place?
     
  4. ernie

    ernie Two Time F1 World Champ
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    Hey Steve

    The reason we disconnect them is because when you get one that goes bad on you it shuts down what ever bank it is on. Almost all of the time it is a bad exhaust ecu that is bad and not the cat that is getting hot.
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    Jan 11, 2001
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    Understood ernie (but that's sort of a separate problem IMO, and VK didn't mention his were giving a false result to the injection ECU).
     
  6. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    Thanks for the responses guys...

    Just to clarify, I have tried leaving the exhaust ECUs connected and I usually get the dreaded "Slow Down" lights go on as well...So, I leave them disconnected to eliminate that problem. I still get the "Check Engine" light on the 5-8 bank anyway.

    The puzzling thing is that although I have disconnected the exhaust ECUs on BOTH sides, only the 5-8 bank gets the "Check Engine" light....Why??? I'm tempted to swap the main ECUs (behind the seats) just to see what happens...The main ECU computers have the same BOSCH part number.

    If anyone knows the correct procedure to erase the fault codes from the main ECUs, please post it here...I don't really know how to do it and maybe others can learn as well.

    Best regards - VK
     
  7. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
    Tejas/Europe/Desert
    Full Name:
    shanb
    I need to go back to the circuit diagram but if I remember correctly, the exhaust ECUs warning circuit is seperate from the "check engine 5-8" warning circuit so an unplugged thermocouple should not trigger that light. I think you have an unrelated problem. Things like 5-8 crank position sensor, 02 Sensor (which you replaced) and air mass sensor come to mind and there are a few others. Is your tach working properly?
     
  8. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    Yes, my tach is working well and redlines fine ;)

    I have read about the crank position sensor wiring going bad and I will attempt to check there next.....I just haven't had a chance to get under the car yet.

    As for the mass air sensor I looked carefully inside the air intake unit and the tiny sensor wires are still intact....I'm not sure what else to check inside the mass air unit....Maybe swapping the air sensors could prove interesting.

    Thanks for your suggestions.....VK
     
  9. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
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    shanb
    Visual inspection can give you some info, but it might be worth looking at the wiring diagram and using your multimeter to check sensor connections for open circuits and odd resistance readings downstream of the check engine light.
     
  10. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,014
    socal
    CPS is critical to car running. IT is a go no go so don't bother if the car is running. Car can run w/o MAF so thats not it. Put key in run position and push button next to ecu's for greater than 10 seconds to erase all codes. Take airbox off and make sure the connections to the o2 sensors are firmly attached. Take them on and off bend the pins to make sure you have good connection. Incresed resisteance in a circuit with por connection gives an "out of range" reading to the ECU and triggers the check lite. Slow down lites are only for exhaust temp issues. thermocouples will bypass the exhaust ecus and trigger check lites and shut down your engie via the ecus if it gets too hot. This is a related but separate issue. Report back to FC is this does not work.
     
  11. fatbillybob

    fatbillybob F1 World Champ
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    Aug 10, 2002
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    Because these are notoriously poor parts and always fail not sometimes fail always. Therefore 348 users routinely work around them.
     
  12. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
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    Okay guys I have some more info on pulling the codes. You may have only pulled one code out of the ECU. After you get the first set of flashes giving you the numbers for the first code you need to move on to get the next code from the ECU. What you have to do is hold the button down again for :02.5 - :05 seconds, then the ECU will give you the next set of flashes for the following code stored in the ECU. At the beginning of each set of code flashes there is a long flash indicating the beginning of the sequence. After all for numbers have been flashed there will be a pause, and it just starts over again, with the long flash indicating the beginning. Now after it has gone through the series of flashes, what you want to do is wait until the last number is flashed, then hold the button down during the long flash :)02.5 sec) and let go in the middle of the pause. This will get you to the next stored code. As I said before the next code will start with a long flash, then a pause, then the flashes start for the next code. You just keep doing this until you have pulled all the codes out of the ECU. When all of the codes have been pull you will get nothing but long flashes. When you are at this point, that is when you want to hold the button down for :10 seconds to clear the codes out.

    I have been having a misfire problem with my car, so today I pulled the codes for my car. I got the 4121, which is the exhaust ecu I have disconnected. Then I got 4114 which is the TDC control unit. The book say you will always get the TDC code when the engine is off. The next one I got was 1444, which is the M.I.L. Okay I looked everywhere and the book doesn't say what the M.I.L. is. I'm hoping this is what is causing my misfire. But the problem is, I don't know what the freeking M.I.L. is, and can't find it in the stupid book!
     
  13. Ricambi America

    Ricambi America F1 World Champ
    Sponsor Owner

    Not to hijack the thread, but which book are you referring to with the codes? I have the WSM, Tech Manual, and Parts for my 348 -- but nowhere (that've I've seen) are the ECU codes listed. Is there a seperate 2.7 Moto book?

    -Daniel
     
  14. airbarton

    airbarton Formula 3

    Nov 11, 2002
    1,462
    Kennesaw, Ga.
    Full Name:
    Chuck Barton
    Here are the codes.

    Hot wire air flow meter 1111
    Engine coolant temp sensor 1112
    Throttle potentiometer 1113
    Lambda sensor 1114
    Lambda regulation Additive value for self adaption 1211
    Lambda regulation multiplicative value for self adaption 1212
    Lambda regulation intake manifold compensation 1212
    Valve 4111
    Injection valve 1 1411
    Injection valve 2 1413
    Injection valve 3 1414
    Injection valve 4 1412
    RPM sensor 1121
    Stroke sensor 4112
    Power module not used 4113
    Battery voltage 1122
    TDC control unit recognition 4114
    Secondary air solenoid valve 1123
    Purge valve 1124
    Catalyzer temp ECU 4121
    Catalyzer temp to high 4122
    Speedometer signal 4123
    Short circuit on idle regulator 1311
    Open circuit on idle regulator 1312
    No error detected 4444
    M.I.L. 1444
    Electronic control unit 1313
    Compressor connection signal 4131
     
  15. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
    Tejas/Europe/Desert
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    shanb
    Hey Ernie - what's up?

    M.I.L. = malfunction indicator light. Which means the system is seeing a failure somewhere in the warning light circuits.
     
  16. ShanB

    ShanB Formula Junior

    Jul 9, 2003
    547
    Tejas/Europe/Desert
    Full Name:
    shanb
    Actually it can run without the 5-8 CPS, but it will run on one bank and be sluggish above idle.
     
  17. ernie

    ernie Two Time F1 World Champ
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    Thanks Shan. I tell you these books are write soooooo poorly.
     
  18. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    I totally agree - especially the 348 Workshop Manuals are very short on descriptions and what to do when there's a problem....

    Thanks Ernie and BilllyBob on the detailed descriptions on retrieving the codes and CPS info....Cudos to AirBarton for posting the explanation of the codes once more.

    Quote - "Take airbox off and make sure the connections to the o2 sensors are firmly attached. Take them on and off bend the pins to make sure you have good connection. "

    BB - the O2 sensors have been changed already so there's no chance the wiring is broken or the connections are loose...I checked them twice with the air box off....Now I will attempt to retrieve the ECU codes based on Ernie's procedure and report back with findings...

    Cheers - VK
     
  19. airbarton

    airbarton Formula 3

    Nov 11, 2002
    1,462
    Kennesaw, Ga.
    Full Name:
    Chuck Barton
    Anyone know how to clear the error codes without having to go through them all first? I have been trying to solve a similar problem by getting the codes. The method Ernie has quoted is correct for retrieving them and erasing them but when I try to do that, the codes seem to be endless. Just how many codes can it store? Is it possible that it has every single error code it ever read because no one ever erased them? If so, it is going to take a long time to go through them all before I can do the 10 second push to erase them. I tried today for almost half an hour and I am still getting more codes. There has got to be another way to erase them without having to go through them all first.
     
  20. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    Charles - sorry I don't know the short-cut to erasing the codes before displying them....However I followed Ernie's procedure and in my car I was able to retrieve the stored codes...Here they are:

    Bank 1-4 ECU (I get NO "Check Engine" light on this bank)

    4121 - Catalyzer Temp ECU (appers to be informational only)
    4112 - Stroke Sensor (no idea yet what that is....)
    1121 - RPM sensor (must be related to RPM ;) )


    Bank 5-8 ECU (I always get the "Check Engine" light)

    4121 - same as above ( my exhaust ECUs are disconnected)
    1111 - Hot Wire air Flow meter (this could be part of my problem)
    1211 - Lamba regulation Additive value for self adaption (Say what??? Anyone knows what this error code means??)
    1121 - PRM sensor on this side also...

    So I have cleared the codes as per procedure and will give it another test later this week. Stay tuned...

    Many thanks to all who have contributed in this discussion - VK
     
  21. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,014
    socal

    Remember that light bulb is out of your car?
     
  22. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,014
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    oldest version of 348 wsm is one book. there are actually 2 wsm's vol1/2 and 2 parts books
     
  23. fatbillybob

    fatbillybob F1 World Champ
    Consultant Owner

    Aug 10, 2002
    19,014
    socal
    BB - the O2 sensors have been changed already so there's no chance the wiring is broken or the connections are loose...I checked them twice with the air box off.

    Cheers - VK[/QUOTE]


    Sorry there is a chance because Ferraris do not know how to do wiring and Bosch sells seconds to Ferrari. You can still have connection but a poor one. A poor connection changes the reading parameters of the o2 sensor to an "out of range" reading thus the MIL etc.... BTW did you problem start after you changed the o2 sensors? There are also some who believe that while the o2 sensor is grounded via one of the 4 eires it is also grounded via the metal of the exhaust system. But this is a crappy ground because there is exhaust pipe gaskets with bolts connection the system and it makes for funny resitence that can change w/ temperature. The solution is to add and additional ground strap from each o2 sensor to the sub assembly. Persoally, I think there is something to this theory and have reasons to make me believe it is a valid one including personal experience. Been there done that it helps

    YMMV just remember if it solves your problem you heard it first from BB.
     
  24. goyal99

    goyal99 Karting

    Mar 5, 2002
    185
    Upstate NY - USA
    Full Name:
    V K
    BillyBob - good suggestion in the grounding...I will check that and see what I can do....To answer your question, no the "Check Engine" light was on BEFORE I changed the O2 sensors...Actually I thought changing the sensors, which were probably factory originals with newer ones, might take care of my "Check Engine" problem but it make any difference....However I did not use new Bosch O2 sensors - I had a used pair in good condition and I installed those...As you can see from the photo I posted earlier in the thread, the slightly used O2 sensor "looks" much better than the darker and heavily used O2 sensor.

    As for the error code 1111 (Hot wire air flow meter), I took out the left Bosch air flow sensor housing and visually inspected the tiny wires (3 heated air flow wires) inside...They appear to be in fine shape, not broken or corroded. The wiring plug and connectors look okay also...Is there an electrical test for testing the values of the sensor/meter while the car is running and under load???? Post it here if you know what the test(s) are and how it's done...

    In the meantime I will attempt to switch the air flow sensors around (left to right) to see if my problem goes to the other bank.

    Cheers - VK
     
  25. ernie

    ernie Two Time F1 World Champ
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    Nov 19, 2001
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