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      02-27-2020, 12:23 AM   #1
Beamerboy101400
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Symptoms my 335i is having

Okay so to kick things off my oil temp gauge Does not move. I've done the system test and seen it move. And did the hidden menu and saw the temps were at operating temperatures. In the hidden menu it says that the coolant temp is -128C which doesn't sound right and doesn't move. When I go into sport mode and Manuel shift the radiator fan spins really loud, like a jet engine loud.


My car has bootmod3 stage 2 tune, catless, charge pipe, intake, intercooler

What is causing these issues
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      02-27-2020, 08:42 AM   #2
im_an_alien
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Quote:
Originally Posted by Beamerboy101400 View Post
Okay so to kick things off my oil temp gauge Does not move. I've done the system test and seen it move. And did the hidden menu and saw the temps were at operating temperatures. In the hidden menu it says that the coolant temp is -128C which doesn't sound right and doesn't move. When I go into sport mode and Manuel shift the radiator fan spins really loud, like a jet engine loud.


My car has bootmod3 stage 2 tune, catless, charge pipe, intake, intercooler

What is causing these issues
Coolant temp sensor would be a good place to start.. when the ECU cannot reliably determine coolant temps, or detects the temps trending higher without a plausible signal from the sensor, the default would be to assume worst case scenario ie an overheated engine, thus the high fan speed.
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      02-27-2020, 08:46 AM   #3
Beamerboy101400
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Quote:
Originally Posted by im_an_alien View Post
Quote:
Originally Posted by Beamerboy101400 View Post
Okay so to kick things off my oil temp gauge Does not move. I've done the system test and seen it move. And did the hidden menu and saw the temps were at operating temperatures. In the hidden menu it says that the coolant temp is -128C which doesn't sound right and doesn't move. When I go into sport mode and Manuel shift the radiator fan spins really loud, like a jet engine loud.


My car has bootmod3 stage 2 tune, catless, charge pipe, intake, intercooler

What is causing these issues
Coolant temp sensor would be a good place to start.. when the ECU cannot reliably determine coolant temps the default would be to assume worst case scenario ie an overheated engine, thus the high fan speed.
That's what I was gonna look in to before I start assuming the worse.
Thank you
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      06-17-2021, 10:07 PM   #4
PBGF32
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Any luck with this? I'm in the -128 club as well with a CEL to match haha
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      06-18-2021, 04:45 AM   #5
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Not sure this will help you (new poster), but I just read that BM3 might be suppressing codes, so maybe code back to stock and see if some codes pop up?
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      06-18-2021, 08:09 AM   #6
tardboi
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Quote:
Originally Posted by PBGF32 View Post
Any luck with this? I'm in the -128 club as well with a CEL to match haha
Transmission heat exchanger thermostat

Or any other coolant temp sensor. For me it was that one though
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      06-18-2021, 10:08 AM   #7
iScramble
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I've had the same issue, new coolant temp sensor and I was good to go. Quick easy fix.
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      07-11-2021, 08:58 AM   #8
PBGF32
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UPDATE: Cleared all codes and instantly everything was back to normal. Oil temp gauge working, no CEL. Have driven 3 weeks without issue.

Initially I tried swapping the ECT sensor near the oil filter housing before I had access to someone with OBII setup and that had zero effect. Still got the same -128 C reading.

It looks like the expansion tank leak caused a short somewhere in that instant and the ECU never trusted the reading again afterwards. Once I cleared the codes everything was perfect. (Never actually swapped ECT sensors, just plugged the new one into the harness as quick data point)
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