bars_sun

2004 545i. Need some advise on what do next - as you can see from the subject thermostat was already replaced. Was pulling off the stop sign today and here is comes again - CEL and "Increased emission" again. Came home connected DIS and read error code. It says again that thermostat stuck open. Well, I doubt that's the problem since it was replaced about a month ago. Some other possible solutions from the DIS test plan were
1. coolant proportion is not 50/50
2. thermostat map needs adjustment (programming required to newer CIP)
other possible solutions after repeats are
1. upper temperature sensor
2. engine harness (oh no!!!)
I had long discussions with my BMW mechanic in the past that in case of some unclear error messages BMW in most cases suggests either reprogram the car or replace engine harness. Replacing engine harness to me is just a little bit too aggressive, but reprogramming might help. Car also developed hairline crack in the coolant expansion tank and tank is going to be replaced within next couple of days. I was thinking to do complete flush of the coolant and refill with fresh mix.
I would like to know if anybody else got that dreaded error message after thermostat replacement.

p.s. I noticed from the past that error message appears to be related to how hard you are pulling off from the complete stop. I don't think this is anyhow related to K&N filter, SB or removal or carbon filter since error first time appeared way before I put any of that in, but started to appear more often after AUX retrofit was done, so must be new CIP loaded during AUX retrofit made conditions worse in regards to thermostat opening map.

Krozi

What about the O2 Sensors?

bars_sun

DIS did not say anything about O2 sensors in the test plan. I don't think O2 sensors would trigger "Thermostat stuck" error message in the diagnostic system.

Krozi

Right.

Taking a shot in the dark here. Is there a way something else is causing the thermostat to fail? How many times have your replaced it?

bars_sun

Just once. I am leaning towards reprogramming car, but would have to wait until another emission error pops up since I have cleared current fault, but do have a printed report from the DIS - dealers in my area are kinda picky and wouldn't trust some dude with report printed from software which suppose to be used by BMW dealerships only.

ricky1329

If you already replace the thermostat. How about the temperature sensor ?

bars_sun

yeah, I don't really have many options here and the only two things I can do without really visiting the dealer are - change temp sensor and flush coolant and refill with fresh mix.

Krozi

Wait so all in all, how many times did you get the increased emissions warning? Just give the thermostat another shot.
I don't think these have a high fail rate but maybe your where just unlucky and got a bad thermo when you replaced it last. .)

bars_sun

After thermostat replacement - this is first time. Before thermostat replaced I got it about 4-5 times (it was averaging about 1-2 times in 6 month). This last winter was the worst one - was getting that error monthly.

I spoke with mechanic and he suggested to replace temp sensor (as being cheapest and fastest ways to eliminate one more possible cause)

TexaZ3

Well, yes, but they might trigger increased emissions fault.