[run4ski4]

My car (2015 335i, N55 engine, m-sport package, 35xxx miles, completely stock) is going into limp mode on cold days (<35 degrees F) and I am perplexed as to what is going on. I have taken it to an indy repair shop and they have suggested replacing a handful of parts but the problem has persisted. Before taking it back to them, I would like your collective wisdom. I bought the car 3 years ago and the problem has occurred each winter.

Situation:

• On cold days (<35 degrees F, 2 degrees C) the car goes into limp mode (limited RPM, fans running loudly) between 5 and 10 minutes into my drive. This is slow city driving and I am not pushing the car hard.
• Using the hidden temperature menu, the coolant temperature reads negative 128 (-128 C). Prior to going into limp mode, this reports the temperature correctly.
• Check engine light comes on with a generic P0128 code (Coolant Thermostat, Coolant Temperature Below Thermostat Regulating Temperature) and U1408. The hidden menu DTC shows only E12C1C. I don’t have access to a scanner for the more specific codes.
• The car is really slow to warm up and this seems to happen when the coolant temperature is less than 60 degrees C.
• Generally speaking, heater isn’t helpful, the air is warmer than the ambient temperature, but still cold (seat heaters are a life saver).
• If I warm the car up in my driveway for about 10 minutes, shut it off, and then restart the car and depart the problem doesn’t happen.
• On longer drives (using the pre-heat method discussed above), the coolant temperature doesn’t get much above 70 degrees C if I am running the heater. If I shut the heater off, the coolant temperature will jump to about 90 degrees C.
• The oil temperature on the dash usually doesn’t budge in a 10-15 minute drive, on longer drives, it makes it to about 190 degrees F (88 degrees C).

Suspected Cause:

• The motor is heating up too slowly to make the computer happy. The computer suspects a problem with a sensor and then goes into limp mode to protect the engine.

What I have done:

• Replaced the thermostat twice (when the first attempt didn’t work, we suspected I had a bad thermostat)
• Replaced the water pump (given the reported water pump problems with this car, I suspected the water pump was out of control)
• Replaced the transmission heat exchanger (hoping its thermostat was the problem)
• Replaced coolant temp sensor on top of block

Any thoughts or suggestions? Thank you in advance!

[thejeremyman9]

Sounds like a sensor, wiring, or potentially even DME issue. If you are getting an erroneous coolant temp reading, i dont see any way its not one of those 3 things. Once the DME sees that erroneous reading, the effects cascade and it likely goes into limp mode kicks the water pump and fan onto high as a protective measure since it doesn't know the true coolant temp.

So you need to try and figure out why you get the incorrect coolant temp reading - everything else is likely due to that.

[njdangelo]

What makes me perplexed with this whole issue is the fact that if you warm it up for 10 minutes without driving then turn it off and back on it works normally. you'd think if it was a sensor you would get the codes and temperature readings in any situation. that makes me wonder if its maybe a voltage thing. Are the lines going in and out of the heater core hot? I only ask because even if you were getting an erroneous coolant temp reading the actual coolant temp SHOULD be hotter which would give you normal heat. Very interesting issue going on here. Does the car display the correct ambient temp?

EDIT: After doing some research the lowest temp your coolant sensor would register is -128 which means you likely have an open circuit fault and the computer isn't getting any information from the sensor. check the harness for loose cables and then check continuity down the chain until you find the break.

[run4ski4]

Thanks to both of you for your thoughts.

There is a part of me that wonders if the whole problem is caused by the car being too slow to warm up. If I warm up the car for 10 minutes, it gives the system just enough of a head start that it warms up quick enough the second time to not trigger the limp mode.

This brings up the question about the order in which things happen: 1) does the temp sensor fault out and this triggers the limp mode? or 2) does the slow warm up trigger the limp mode and this does something wonky to the temp sensor output in the hidden menu?

I don't know if this will be helpful or not, but if I hook the car up to my computer via an obd-II cable to OBDwiz, I can still get a reading on the coolant temperature even when the hidden menu temperature says -128.

[DominikaHosniak]

How many liters/100km N55 ?

[pshovest]

Working fine after idling for 10 minutes, which raises the underhood temperatures, makes me wonder if the DME is temperature sensitive. You need to scan with ISTA or something BMW capable. There was a similar thread about an N55 with low coolant temp and fan running full speed on another forum. Was that you? I had an E30 with a temp sensitive DME. I was able to put it in the freezer to cause the problem, then heat to 150F in oven to make it go away.

[thejeremyman9]

Originally Posted by run4ski4

Thanks to both of you for your thoughts.

There is a part of me that wonders if the whole problem is caused by the car being too slow to warm up. If I warm up the car for 10 minutes, it gives the system just enough of a head start that it warms up quick enough the second time to not trigger the limp mode.

This brings up the question about the order in which things happen: 1) does the temp sensor fault out and this triggers the limp mode? or 2) does the slow warm up trigger the limp mode and this does something wonky to the temp sensor output in the hidden menu?

I don't know if this will be helpful or not, but if I hook the car up to my computer via an obd-II cable to OBDwiz, I can still get a reading on the coolant temperature even when the hidden menu temperature says -128.

Wait so if you read data through the OBD2 the coolant temp is reading normally even if the hidden menu is not?

Originally Posted by pshovest

Working fine after idling for 10 minutes, which raises the underhood temperatures, makes me wonder if the DME is temperature sensitive. You need to scan with ISTA or something BMW capable. There was a similar thread about an N55 with low coolant temp and fan running full speed on another forum. Was that you? I had an E30 with a temp sensitive DME. I was able to put it in the freezer to cause the problem, then heat to 150F in oven to make it go away.

This is similar to where i was going - a lot of electronics can be temperature sensitive, but the DME should have not problem with his temps, given people drive in much colder temps without issue. So if it is the DME, there is an underlying issue.

[pshovest]

Sure, if the problem is the DME, the underlying issue is the DME has a defect. It could be a bad solder joint or a cracked component that opens on low temp. The freezer and oven will sort this out quickly.

[njdangelo]

Originally Posted by run4ski4

Thanks to both of you for your thoughts.

There is a part of me that wonders if the whole problem is caused by the car being too slow to warm up. If I warm up the car for 10 minutes, it gives the system just enough of a head start that it warms up quick enough the second time to not trigger the limp mode.

This brings up the question about the order in which things happen: 1) does the temp sensor fault out and this triggers the limp mode? or 2) does the slow warm up trigger the limp mode and this does something wonky to the temp sensor output in the hidden menu?

I don't know if this will be helpful or not, but if I hook the car up to my computer via an obd-II cable to OBDwiz, I can still get a reading on the coolant temperature even when the hidden menu temperature says -128.

I don't think there is really a way for a car to warm up faster or slower if it's just idling in your driveway. I feel like driving it would warm it up faster, no?

[run4ski4]

Originally Posted by thejeremyman9

Wait so if you read data through the OBD2 the coolant temp is reading normally even if the hidden menu is not?

Correct, the hidden menu will show -128 but I can still get a reasonable coolant temperature via the OBD2. This makes me think the -128 displayed may be a computer thing rather than a sensor thing.

Originally Posted by njdangelo

I don't think there is really a way for a car to warm up faster or slower if it's just idling in your driveway. I feel like driving it would warm it up faster, no?

I fully agree, driving should warm it up faster. However, in this case I shut the car off after warming it up and then restart it before leaving. Because the car is warmer when it restarts, my speculation is that it gets to a reasonable temperature more quickly avoiding whatever it is that triggers the limp mode.

[run4ski4]

As I step back and think about this, it is sounding more and more like a problem with the wiring heading to the electrically controlled thermostat.

I imagine BMW set things up such that any problem with the voltage, etc, the thermostat will default to completely open. If the thermostat is always open, it would explain why I am so slow to come to a normal operating temperature and have very little heat. This may be triggering something in the computer that sends me to limp mode.

I will visually inspect the wires heading to the thermostat. Also, is there anywhere I could look to get more information about the expected voltage at the thermostat? The voltage probably changes as the coolant temperature fluctuates.

Thanks again for all of your thoughts on this.

[pshovest]

Originally Posted by run4ski4

.........it is sounding more and more like a problem with the wiring heading to the electrically controlled thermostat.......

The DME commanding thermostat open is probably the effect and not the cause. In a functioning car, the DME will send 12v to the thermostat when it senses high engine load. This opens the thermostat and lowers coolant temp during aggressive driving. You can unplug the thermostat as a test.

It seems more likely that the DME loses the engine temp reading, (-128 ... open circuit) and then goes into full cooling mode.....fan speed high, 12v to thermostat to fully open, limp mode to prevent WOT and protect the engine.

I would check the connections on the coolant temp sensor for corrosion and any evidence of wiring problem at connector. If this looks OK, change the sensor, it's inexpensive. Check connections at DME, confirm wiring continuity from sensor to DME.

Scanning with a BMW capable tool is essential.

Here's the other thread I mentioned earlier about a similar issue, -128 temp, fan runs fast, engine doesn't warm up. This is on an N26 engine rather than N55.
https://www.bimmerfest.com/threads/t...n-open.1422117

[thejeremyman9]

Originally Posted by pshovest

The DME commanding thermostat open is probably the effect and not the cause. In a functioning car, the DME will send 12v to the thermostat when it senses high engine load. This opens the thermostat and lowers coolant temp during aggressive driving. You can unplug the thermostat as a test.

It seems more likely that the DME loses the engine temp reading, (-128 ... open circuit) and then goes into full cooling mode.....fan speed high, 12v to thermostat to fully open, limp mode to prevent WOT and protect the engine.

I would check the connections on the coolant temp sensor for corrosion and any evidence of wiring problem at connector. If this looks OK, change the sensor, it's inexpensive. Check connections at DME, confirm wiring continuity from sensor to DME.

Scanning with a BMW capable tool is essential.

Here's the other thread I mentioned earlier about a similar issue, -128 temp, fan runs fast, engine doesn't warm up. This is on an N26 engine rather than N55.
https://www.bimmerfest.com/threads/t...n-open.1422117

This is exactly what i was saying above about cause vs effect.

[run4ski4]

Thanks for your thoughts and sending me to the other thread with similar issues.

I visually checked all the wiring/connections last night and the problem continued on my way to work this morning. My next steps will be to get a replacement coolant temp sensor and get the car scanned with a BMW capable tool.

[KDW4him]

Originally Posted by run4ski4

This may be triggering something in the computer that sends me to limp mode.

I will visually inspect the wires heading to the thermostat. Also, is there anywhere I could look to get more information about the expected voltage at the thermostat? The voltage probably changes as the coolant temperature fluctuates.

By limp mode would you mean you cannot go over 2000 RPM? When mine had a bad thermostat the codes read stuck open so the computers would let you drive the car just not over 2000 RPM. If I were to slightly gas it as in eco mode the car would drive semi-normal but upshift at 2K.

[run4ski4]

Correct, the car won't let me go over 2000 RPM and the coolant fans come on at full blast (presumably to keep the car from overheating).

My initials thought was a problem with the thermostat but replacing it hasn't solved the problem.

[KDW4him]

Originally Posted by run4ski4

Correct, the car won't let me go over 2000 RPM and the coolant fans come on at full blast (presumably to keep the car from overheating).

My initials thought was a problem with the thermostat but replacing it hasn't solved the problem.

Have you also replaced the water pump?

[mazen222]

I noticed a very limp issue on my car as well in cold weather. It was mostly when i go from stop to accelerate, the car advances very slowley and then gives me back the power (2 seconds after i press accel.)

I assumed this is to avoid slipping on cold icy roads since im rwd... This does not happen when its warmer.

Perhaps its something related to this?

[run4ski4]

Originally Posted by KDW4him

Have you also replaced the water pump?

Yes, I replaced the water pump but, unfortunately, it didn't seem to make a difference.

[Foxtrot3Zero]

Hello,
Very sorry for your troubles. I wanted to just share with you how I handled the same type of issues on my car (2013 N55 M-Sport). However, please understand this worked for me and my car. I had the same exact issue as you but lacked the temperature element you are noting. I felt my issues are common enough to share. This remedy might not work for you though. I'd hate to have you continue to fall into the trap of "throwing parts" at the problem.

I had several limp modes on my car. I live in Florida so the temps weren't as low as yours but were cool for Florida (60's). Extremely high fan speed/loud, can't get over 2,000 RPM in lower gears, Oil guage on dash sticking at low value.

I read several posts about N-55 limp modes here on forums that were not track day related. Initially, it appeared this only affected 2013 M-Sport N55 models. However, as time went on, members with other model years chimed in with same issues (although not as many). Almost everyone (including me) could stop/shutoff car, restart and the problem would go away. I saw folks permanently solved the problem through a single or combo of the following:

1. Re-flash ISTA to newest avail version,
2. replace fan relay,
3. replace 850W fan.

The fan replacement is linked to fans produced up to November 2013. After that date of manufacture, they are supposed to be good. The date of manufacture is on the fan module. The relay was helpful to some and not for others. The ISTA flash was helpful to several folks. This is what I tried first and it worked for me - no more issues. I did the flash first (at Indy not BMW to avoid potential lock-out issues) because it was the easiest first step for me, and I wanted to try one remedy at a time.

I wanted to share because of similar issues, but realize my ambient temp is nowhere near what you are dealing with which could make it something completely different. Sorry! Best of luck.

[Foxtrot3Zero]

This is what I read through:

https://f30.bimmerpost.com/forums/sh...irst+limp+mode

[pshovest]

Interesting. Thanks for the info and link.
Here are the (2) SIB's referenced.
Both have specific codes that should be stored in the DME.

Edit: Note that one the SIB's refers to cars with 0337 M-Sport package and the other does not.