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11-23-2020, 03:33 PM | #1 |
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Coolant temp and thermostat codes
So, I've been getting following codes in the AM on the way to work when it is colder (40F or below).
348A - MAP Thermostat jammed open 293E - Coolant temperature sensor: multiple fault There is no SEL but the fan goes to max. I can monitor via MHD and the repeatable sequence goes like this: 1. Start car. No codes issues. Coolant temp and oil temp goes up slowly. 2. About 5 miles down the road, coolant temp starts to go up faster than oil and the codes are thrown. Coolant temp will keep going up to over 200F while oil temp remains low and slowly rising normally. Transmission temp also goes up normally. 3. I pull over, turn off car, clear codes, restart car, and coolant temp is immediately below oil temp an then behaves normally the rest of the way to work (about 20 miles) Car also behaves fine on the way home (temps start about 90F when I am coming home). I replaced the coolant temp sensor but no change in behavior. Water pump was replaced about 40k ago, before I owned the car, but it's not clear if the thermostat was replaced also. I have a CSF radiator now which I know can cause the computer to think there is a problem due to it being more efficient, but I have the same radiator in my 335 and...no issues.. I understand the thermostat heater issue and that that may be the cause. The part that is baffling is that the coolant temp *instantly* goes to normal when I reset the codes. Makes me think it is the wiring, but wouldn't that randomly cause issues not have a perfectly reproducible pattern? Not sure which code is the chicken and which is the egg...to strain a metaphor. Anyway, I think I will just replace the water pump and thermostat and see what happens, but it will be frustrating if it doesn't fix it. Willing to listen to any ideas. Right now the problem is just an annoyance. TIA.
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11-23-2020, 07:06 PM | #2 |
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Check/clean grounds first.
Then go through the air bleed procedure ... could just be air in the system. IIRC you can do a waterpump test with INPA. If not I know you can with ISTA/D. |
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11-23-2020, 09:30 PM | #3 |
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The replacement of the water pump and/or thermostat won't help. I've tried. Don't waste your money. I too run the CSF radiator and I have the exact same problem since I installed it. Anytime it is below 45 F, the car will throw the codes, and I also had the fan turn on high even though clearly the car isn't overheating. Took the car to an independent BMW shop and they tried all sorts of things to run down the issue. Replaced water pump, thermostat, traded out the stock radiator and CSF radiator multiple times. They could never run down the issue though they could repeat the problem over and over. I have never found a fix for it other than taping up the kidney grills and leaving about an inch of clearance for air flow. When I do that, the car runs great and it warms up normally. I have talked with CSF about this and they couldn't provide a solution. I discussed with Bimmerworld as well, which is where I bought the CSF Radiator from and they couldn't provide any guidance as well. I put the radiator in at the beginning of 2019 and experienced the issues both during the first couple of months with cold weather (mostly cold mornings) and then at the end of 2019 with the cold months. I've posted a thread about this in the Track Section if you want to search for it.
Ultimately, it is not something that is wrong with your car, it's just an issue with the radiator and the way the 135i thermostat/cooling is programmed. Last edited by mKilgore; 11-23-2020 at 09:35 PM.. |
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11-23-2020, 10:16 PM | #4 |
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Wow...that sucks. The only thing I didn't see you mention is replacing the wiring harness piece to the temperature sensor. I'll go check the thread out...is anyone else duplicating this?
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11-23-2020, 10:35 PM | #5 | |
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I'll try the air bleed procedure again, but it worked fine after the rad replacement and the rad has been on for months and been through multiple track days...pretty sure I'd have seen a cooling issue then if I had an air problem. Are you talking about checking grounds on the battery?
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11-23-2020, 10:38 PM | #6 |
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1. Does anyone know which wiring harness has the coolant temp line on it? Sensoric module 1 or Sensoric module 2? Thinking of getting a used one off of ebay to swap out - the rotating connection for the temperature sensor on the N55 (N54 seems to not use this type of connector) could be causing intermittent contact.
2. I am also going to try to switch which cooling mode MHD is using to see if it has an effect.
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11-24-2020, 11:29 AM | #7 | |
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If the theory is that the radiator is causing the problem than that would show a resolution right? Edit** NVM, went to the track section and it was near the top of the list, I see replacing with stock did fix the issue... |
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11-24-2020, 03:11 PM | #8 |
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Switching MHD to sport cooling didn't help. Actually caused it throw the codes 3x this AM vice the usual one.
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11-25-2020, 02:24 AM | #9 |
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So, in looking at the N55 pdf, in the cooling system diagram on page 75, I don't see how actual coolant temp could rise as it has appeared to without a problem with the temperature sensor or it's wiring. Even if the thermostat was forced open by the ECU because it didn't believe the lower heat-up rates provided by the CSF Radiator, I do not see how actual temperature at the OFH could go up...it appears to sense coolant temperature in the main channel going to the Radiator, not just exclusively the bypass line going out the front to the thermostat, which I could see heating up if that flow path was severely restricted. This seems to be confirmed by the fact that, when I stop the car, reset codes, and restart, sensed temperature goes immediately from a max of 226F (it almost always goes to 226F and stops, which seems like an ECU failsafe for "I don't know what temperature is") to something less than oil temp (typically 115-130F at that point), which would be a realistic temperature for coolant with pump and fan on high(which is the response action by the ECU for the codes). I also opened the expansion tank this AM with the car running and it was clearly not at 226F. It also had excellent vent flow, so the pump is definitely working as well. If anyone sees a different logic here I should be following, please chime in. I think my next step is replace the wiring to the sensor, as I've already replaced the coolant sensor with new. I have to admit that rotary coupling appears to be a prime "intermittent failure" point.
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11-25-2020, 09:16 AM | #10 |
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Seems logical, but my only response is why does this issue not arise at higher ambient temps if the wiring is faulty? It seems like it would be an issue no matter what the ambient temp is. But I am also intrigued as to whether changing the wiring could fix the issue, so please feel free to try it haha.
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11-25-2020, 10:43 AM | #11 |
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T-stat value is 205F with a variable 20 degree swing based on emissions and cooling targets directed by the DME. If coolant temps are under 225 or so, you're totally fine. The DME does weird things, especially in traffic/low speed driving.
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11-25-2020, 11:30 AM | #12 | |
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11-25-2020, 11:33 AM | #13 | |
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BTW, I appreciate you weighing in...I know you have moved on from the 135 but your knowledge on the platform is acknowledged. Stoptechs and splitter you sold me are still going strong! Keep poking holes in my ideas...helps me to clarify/correct my thoughts process. Last edited by AndyW; 11-25-2020 at 11:44 AM.. Reason: Typing on my phone, lol |
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11-25-2020, 06:40 PM | #14 |
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Here's a log of the phenomena.
https://datazap.me/u/andyw/coolant-t...og=0&data=5-12 It is just a short ride to pick up my son from work. The lowering coolant temp in the early data may be a clue...that may be what is confusing the DME. Still not sure it it is real temp or not with the 293E code. Here is a log idling in the garage after I reset codes and restarted. I jggled the connector for a bit with no effect, then, to see what would happen, I disconnected the coolant temp sensor. You can see what happened.. It threw the same 293E shadow code as well aS 2937 coolant temp sensor - short circuit. The car also stumbled a bit then went to a high idle. https://datazap.me/u/andyw/coolant-t...og=1&data=5-12 More puzzled than ever. |
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11-27-2020, 11:57 PM | #15 |
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Of course, in the last two trips...no codes. Sigh.
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11-29-2020, 03:04 AM | #16 |
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Sounds like when it's cold out the CFS radiator is so "efficient" that the coolant temps are below the target the DME is looking for and it throws that code. The DME thinks the sensor is bad b/c the temps are too low.
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11-29-2020, 11:40 AM | #17 |
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This makes sense. The only part of this that doesn't answer it fully for me is that I can watch the measured temperature go up so I am not sure if that is a *result* of the thermostat being fully open, making the thermostat the cause, or if the sensor or wiring is the problem, causing the thermostat to go wide open. Another way to say it: If it was just a DME fault, why does indicated temp go up while flow is actually going up (TSTAT full open)?
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11-29-2020, 12:58 PM | #18 | |
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11-29-2020, 01:51 PM | #19 |
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Definitely a possibility...but either the computer or the sensor is changing indicated temperature. I am just trying to figure out which!
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11-29-2020, 03:06 PM | #20 | |
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11-29-2020, 07:40 PM | #21 |
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That was step 1...done.
No change in behavior.
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12-01-2020, 11:18 PM | #22 |
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Temp was 32F this AM. Had to clear codes three times.
Here is the log from the coffeeshop where I reset the first time to the second set of codes and temperature spike while on the road. This is a typical log when it happens. https://datazap.me/u/andyw/tstat-cod...data=5-7-12-20 Note that coolant temp goes down from 133F to 127F when I pull out onto the 50MPH road due to the cold ambient (around 34F). I think this radiator efficient is what may be throwing the computer off. I don't know how to log the actual commands to the TSTAT, but I suspect it closes the thermostat (bypasses the radiator more) if coolant temp goes down. When coolant temp does not respond by going up after a period of time, the DME thinks something is wrong. At time mark 253. you can see coolant temp spike...with no corresponding change in oil temp (would be expected to rise faster if TSTAT was really stuck in bypass, but it goes *down*, consistent with a TSTAT that is actually fully open (sending flow to the RAD). I paid attention to the sensed coolant temperature after I turned off the car, then activated it (double press start without brake) for two conditions. 1. Before clearing codes - The sensed coolant temp was still 210F. 2. After clearing codes, before starting car (initiating flow). Sensed coolant temp was now 113F. This was also consistent with sensed temperature after I started the car and I believe, reality. I wish I knew what the car did electronically with the TSTAT at startup as that would likely shed some light on the subject. Of note - it looks physically, like the coolant temperature sensor is in the flowpath to the bypass line, not the main line. Has anyone who has had an N55 apart noticed if this is correct or not? Still baffled.
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