Thermostat fault, SIB 12 15 05, 2EF4

Hi everyone,
I have had a couple of check engine lights related to the thermostat. The dealership replaced the thermostat last Summer sometime, and when I took it in again this week for the light re-appearing, they said it was thermostat related, and that SIB # 12 15 05 said to replace the coolant temp. sensor and the Engine Harness. The engine harness replacement was quoted just over $2,000 grand. My third-party warranty is paying for it. However, I have never heard of anyone on here talking about having to replace the engine harness for this issue. I am afraid that the dealership has mis-diagnosed, AGAIN. I don't have the P code from the ODB, because I have been constantly getting a check engine light for a fuel vacuum leak or DTML pump, and the dealer had not been able to figure it out. So when the light came on this time, I didn't get the codes pulled at AutoZone, but just took it directly to the dealer, since I needed them to swap my Summer and Winter wheels and tires anyways. I should have gotten the codes pulled, because I asked the Service Advisor for them, and he gave me 2EF4. I thought it was usually a P-code.

Anyone had this issue, or seen anything related to this SIB?

Do you have any symptoms besides check engine light?

They want to spend your money for you... . I think you need to have your issue checked elsewhere. They can't figure out what's wrong with the DMTL pump whether it's the pump, check valve, canister or gas cap... but they nailed it right down to the harness for the 2EF4 for thermostat mapping? Wow... What did they do last time?

Agree, need to find someone else for diagnostic other than that dealer. Ask them what does error code "OU812" mean???

Originally Posted by MachtSchnell

Do you have any symptoms besides check engine light?

I noticed oil leaking after their World Class inspection, lol, so I had it there for that. That was the oil switch and oil vacuum pump. Really no other issues. Well, the engine seems sluggish at times, but I think it's that crappy unpredictable trans. Sometimes the car feels like a race car, ready to jump off the line, and other times, sluggish throughout, but I know they will never diagnose that.

Originally Posted by Nube1kenobi

They want to spend your money for you... . I think you need to have your issue checked elsewhere. They can't figure out what's wrong with the DMTL pump whether it's the pump, check valve, canister or gas cap... but they nailed it right down to the harness for the 2EF4 for thermostat mapping? Wow... What did they do last time?

Yeah, exactly what I was thinking, lol.

Originally Posted by MSAMMY

Agree, need to find someone else for diagnostic other than that dealer. Ask them what does error code "OU812" mean???

Yeah, it seems to be slim pickings up here. I have a couple of places I may check though.

I allowed them to proceed with the repair of the engine harness, since the warranty covered it. I had a $100 deductible for the warranty though. Hmmm, how long until the lights comes back on, lol.

Originally Posted by Nube1kenobi

They want to spend your money for you... . I think you need to have your issue checked elsewhere. They can't figure out what's wrong with the DMTL pump whether it's the pump, check valve, canister or gas cap... but they nailed it right down to the harness for the 2EF4 for thermostat mapping? Wow... What did they do last time?

They did perform a test plan for the DTML related issue. They said that it was a leak test, and that there were no leaks. Any ideas on that issue as well?

The BMW FC 2EF4 code equates to the universal P0128 P-code, which usually means the Coolant Thermostat is getting a signal that the coolant temp is below the regulating temp - possibly the temp sensor or the thermostat itself - fast forwarding to the harness assumes they found high resistance, conductor, connectivity or physical connection retention issues. The vacuum leak / check engine light could be a separate issue altogether. Let's play with that one. When does it happen? Any check codes in iDrive?

I got same thing as OP. One week ago i brought car for thermostat fault ( I did read it), so BMW dealer replaced thermostat, then after i got car back 1.5 day later again check engine light. I read a code it was same thing p0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature). Well after keeping car for almost a week they told me it's engine harness.

So I guess these mechanics are pulling connector while holding harness and torn harness a part. It's not a big deal when you have warranty, but if not then it's bad thing we should not pay for this.

Well I had conversation with shop foreman, he had actually told me, that problem with V8 harness (sensor) is very common and reason is silicon shorting pin on connectors. So soon or later all early V8 will have this problem, but the problem was address from 2010 and up.
So if you have thermostat code and you are already replace this, then next is harness (600 dollars just parts). I suggest to you read your store code see if you have at least ones a thermostat fault.