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355 Code P1448 Every 50 Miles

Discussion in '348/355' started by sgtpeper, Jul 19, 2020.

  1. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Yep, that's why the mechanic ordered 3 so we can eliminate that as a cause.

    How do you check the fuel trims?
     
  2. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Another clue-

    During the PPI in Florida, the car did have codes for Catalyst left and right below threshold and central cat failure - which he said was due to the bypass controller.

    The solution was adding O2 extenders which seems to have solved that for a bit at least. It did not have a slow down light on though.
     
  3. Zamboniman308

    Zamboniman308 Rookie

    Feb 2, 2020
    10
    Full Name:
    VanHyfte
    It should be available in the ODBII sensor info with the codes. Not all readers/apps may present it. It's usually with the O2 sensor data etc.
     
  4. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    What sort of readings should I see?
     
  5. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
    3,655
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    Ian Riddell
    OK, I thought that this wire had damage, too?

    Image Unavailable, Please Login

    Is that wire diagonally opposite to the damaged wire? The heater wires are diagonally opposite each other.
     
  6. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    That is just some of the insulation threads. The wire was fine. I'm honestly not sure if that wire is opposite the exposed one. I have a lot of tape on that temporarily...

    I did just swap to ECUs on the right side, started the car, still has a slow down light. Do I need to drive it to really know if it will go off or not?
     
  7. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Oh and I checked the code after I let it run for 30 seconds and it still had the same code as before swapping ECUs
     
  8. Zamboniman308

    Zamboniman308 Rookie

    Feb 2, 2020
    10
    Full Name:
    VanHyfte
    Closer to zero and balanced on the fuel trims.. but more of a curiosity than anything I don't want to get your thread off track.
     
  9. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    I doubt it. Even if the light was latched by some kind of logic, I'm sure it would have cleared with your last reset. I guess, now, the thermocouple probe itself must be faulty... or the wiring... or, hopefully not, the Motronics ECU.

    I just realised it's probably pointless doing a resistance check on the thermocouple unless it is completely open circuit. I was earlier thinking of a negative temperature coeoffient (NTC) type sensor, but the thermocouple most likely has a bi-metallic element which actually outputs a voltage when heated.
     
  10. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Soooooo I decided to clear the P1445 code one more time to see if that does anything.

    After the code was cleared, I tried starting the car and it started and stalled the first time. I tried starting again and it started perfectly and SDL is gone!

    Does that preliminarily point to the right bank cat ecu being the culprit?

    Thanks,
     
  11. Zamboniman308

    Zamboniman308 Rookie

    Feb 2, 2020
    10
    Full Name:
    VanHyfte
    Likely and after driving a few times i expect you will get a 1448 code and CEL light
     
  12. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Isn't this even odder since my whole problem started with a consistent P1448 code? Wouldn't that have pointed to that ECU being bad too?
     
  13. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    That P1448 code can be caused by a number of things, including the valve, vacuum problems, wiring.

    Maybe you need a few more short drives to see if the SD light comes back or the CEL appears. At least warm up the car to get the engine into closed loop mode.

    Since you had that P1448 code before, it probably would have been a better idea if you swapped the L & R main cat SDECUs rather than the two on the same side.
     
  14. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    I thought about that, but I didn't want to remove the ECU as it seems pretty tight in there and I don't have my home lift yet.
     
  15. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Well, we have a result - I started the car again, no code. I took it on about a 2-3 mile loop. The SDL started flashing about a mile from my house, then went solid, then I finally got one bank shutting down. Then it went off on it's own and was fine for a few more blocks, then back on with bank shut down when the light went solid. It didn't go away for another mile so I shut down the car, restarted it and it was back to normal. Went about another mile and it came on in my alley but no bank shut down.

    I checked for codes after I parked and now I have P1446. So definitely something new!
     
  16. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    AND more results - I swapped the ECUs back and cleared the code and started the car - no SDL now. I drove the car about 10 miles including highway speeds all the way into 6th geat - no SDL.

    Pulled in the garage - scanned for stored codes - no codes!

    So my thoughts:
    1. I think the Central Cat ECU is bad and causing the original P1448 as it was clearly causing a SDL intermittently when I swapped the ECUs
    2. I must have not plugged in an O2 sensor properly after one of my tests which must have been causing the SDL with no bank shutdown.
    3. Now I need to drive the car a bit and see if it blows fuse 22 again.

    Does this follow? Am I missing anything?
     
  17. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    I thought you only swapped those yesterday? You were getting an SD light in post #101 (Thursday?). By swapping ECUs, do you mean you swapped the wiring over on the right side?

    SDL or CEL? I thought we discredited the theory that disconnected O2 sensors caused SD lights. i.e. default O2 settings caused no serious changes to fuelling. Maybe we have to come new theories? :p Or maybe there is just some random factor at play here.

    I think we have to wait until you get the new SDECUs and some longer drives before jumping to conclusions.
     
  18. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    I just drove the car another ~20ish miles or so - no SDL or CE light and I checked the codes and nothing showed up. So, feeling promising so far. The #22 fuse also was warm after the drive but not blown!

    @Qavion - Yes, I swapped the wires on the right side. And for #2 - SDL was what I was referring to since it was blinking on start before. Now the car seems to be running just fine.

    I'm wondering if my thermostat is actually bad and on extended highway drives I'm not getting up to temp and therefore the cats are running cold and causing the fuse to blow? OR maybe it really was the bare wire I found...

    FIngers crossed...
     
  19. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    #169 Qavion, Aug 1, 2020 at 10:32 PM
    Last edited: Aug 1, 2020 at 10:39 PM
    There's probably 0.5 ~0.75 amps running through the fuse (at least with a cold exhaust), so I would expect some heat.

    After re-reading the manual, I see my understanding of the electrical heating system of the O2 sensors is not quite up to par. I assumed that the ECU would switch off the heaters after the water temperature was hot. This is not the case. I think the manual is saying that heater current reduces as the exhaust gas heats up the probes (andtheir heater elements). The heater elements are made of a metal with a positive temperature coefficient (i.e. electrical resistance increases with heat and you would expect the current flow to be reduced... so colder fuse).

    This raises an interesting question. Do O2 extenders affect the heating of the heater in any way? If so, might extenders cause the heater current to remain higher?

    Same here :p
     
  20. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
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    Some further clarification:

    I did say this earlier...

    The ECU does control the relay which turns on the O2 heaters, but I realised later that the logic for turning on the heaters is the same as the logic required to turn on the fuel pump. Obviously you don't want the fuel pump to to turn off when the engine is warm.

    Summary: The ECU does control voltage to the heaters via a relay, but as mentioned above, I believe the heater current is subsequently controlled by the exhaust heat, not via a relay.
     
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  21. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    Another 20 miles on it today and no codes of any sort! It drove great.

    I did check oil when I got home and noticed when hot it's a bit overfilled. I should probably suck some out with a turkey baster no?
     
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  22. Qavion

    Qavion F1 Rookie

    Feb 20, 2015
    3,655
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    Ian Riddell
    Turkey baster, yes. I hear overfilled tanks cause all sorts of engine problems.

    Your mechanic is going to be very disappointed )
     
  23. sgtpeper

    sgtpeper Formula Junior

    May 4, 2004
    271
    Denver
    He'll be really happy! He's so backed up. I do think I'll replace the center cat ECU though as it is definitely not super happy.
     

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