[run4ski4]

Problem solved!

After fighting this for the last two winters, the problem turned out to be the radiator. After an accident three years ago, the radiator was replaced with an aftermarket part that, after much testing, turned out to be the problem.

I ended up taking the care to my favorite indy repair shop (LMS Motorsport in Hudson, OH) and they went through every step imaginable to figure out the problem. They updated the software, checked the thermostat, sensors, water pump, and eventually used a thermal imager
and an identical car to show that the computer and thermostat were functioning correctly. In the end, the only remaining piece of the puzzle that we couldn't rule out was the radiator. Once we replaced this, everything works perfect. A similar problem existed on E30 cars that led us to question the radiator. It was so nice to drive to work this morning with a heater and the coolant temperature hovering around 225 F.

Much appreciation to LMS for going above and beyond to sort all of this out. Also, thanks to all of you for contributing and offering your thoughts.

[pshovest]

Glad it's working for you, but it's very difficult to see how the radiator caused -128C coolant temp reading. My bet is on the firmware update, or it's not cold enough for the issue to act up again.

[run4ski4]

The radiator solving the problem was surprising to me too. After updating the firmware (but before replacing the radiator), the problem persisted.

The radiator on this car has more than the traditional in/out ports and we suspect something internal was allowing coolant to flow down the wrong path and bypass the thermostat (which was working as it should). When the coolant failed to come to temperature within a specified amount of time, the car's computer realized there was a problem resulting in the limp mode and -128 coolant temperature reading.

I don't completely understand the magic behind this, I am just glad I didn't have any problems on my way to work this morning when it was 20 degrees (F).

[KDW4him]

Originally Posted by 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.

This says "When driving with high outside ambient temperatures," Isn't the issue when it's cold out?

[pshovest]

Originally Posted by KDW4him

This says "When driving with high outside ambient temperatures," Isn't the issue when it's cold out?

The point was that the OP has neither of these codes, so the SIB doesn't apply.