P0128 and P0118

[jesseusmc73]

Hello
Currently dealing the joys of bmws and Im trying to start driving my car again but dealing with overheating issues. Car is throwing P0128 and P0118, I have changed the thermostat and the coolant sensor but still no dice. It overheats when its sitting idling but stays pretty normal when moving. Ive noticed the fans do not kick on even when the A/C is on. I have tried to wire power to the fan plug just to get it to turn on but I got nothing. I'm not sure if the fans bad, if the system isn't bled properly, or if its the sensor isn't reading. The car was just sitting for a year before I got around to it, this didn't happen while I was driving or anything like that car just decided to not work anymore.

Car is an 08 E92 M3 80k miles

Any help is appreciated!

[dpaul]

Originally Posted by jesseusmc73

Hello
Currently dealing the joys of bmws and Im trying to start driving my car again but dealing with overheating issues. Car is throwing P0128 and P0118, I have changed the thermostat and the coolant sensor but still no dice. It overheats when its sitting idling but stays pretty normal when moving. Ive noticed the fans do not kick on even when the A/C is on. I have tried to wire power to the fan plug just to get it to turn on but I got nothing. I'm not sure if the fans bad, if the system isn't bled properly, or if its the sensor isn't reading. The car was just sitting for a year before I got around to it, this didn't happen while I was driving or anything like that car just decided to not work anymore.

Car is an 08 E92 M3 80k miles

Any help is appreciated!

You can't get the fan to run by just putting 12v on it - there's electronics inside that needs a signal from the DME. Just hope you didn't destroy it by choosing the wrong terminals. In any case, those codes are not what you'd expect if the fan was bad.

Your DME thinks the signal from the temp sensor is out of range - likely resistance too high, which is also interpreted as too cold, which leads to the secondary "stuck open" thermostat code. Low coolant can also lead to this condition but engine cooling is apparently normal while under motion.

So it is not likely there is any problem with the fan or the coolant levels.

This seems like an electrical issue to me. Since you've replaced the thermo and sensor without resolving the issue, I'd unplug the relevant connectors and spray in contact cleaner. Check for patency of the wiring between sensor and DME. Check the common ground for the sensor and DME (X6464)

[CTMike]

When mine was overheating with similar symptoms, had the fan replaced and relay under passenger footwell replaced, but the issue wasn’t solved until the mechanic traced the contacts all the way back toward the battery and found a loose contact. Once that was addressed, fan has been working perfectly and no more overheating.