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Old 06-04-2015, 11:04 AM   #1
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Join Date: Jun 2015
Location: Appleton, WI
Posts: 1
My Ride: 2001 BMW 330ci
Thermostat Jammed Open

My 2001 330ci has 37k miles. Purchased 6 mos ago. I have put 2k miles on it.

I keep getting check engine light. Peake code reader says: "Thermostat Jammed Open." The temp gauge reading is ALWAYS normal. After normal warmup it reads "dead center" Heater works fine.

I have done the following.
1. Installed new engine block temp sensor
2. Installed new thermostat
3. Installed new temp sensor in lower radiatior hose.
I did each of these 3 items separately and none seemed to have any effect.
The check engine light comes back after a few trips and the only code on the Peake is "thermostat jammed open"
I am at the end of my rope.
Any thoughts will be appreciated!
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Old 06-04-2015, 11:30 AM   #2
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Join Date: Apr 2010
Location: Murrieta, CA
Posts: 9,296
My Ride: '94 325iC & '00 323i
Are you resetting the engine computer after you finish working?

Did you use the right t-stat?

Your issue should be specifically the t-stat, not the other things you are doing. The M54 uses an electronic t-stat that puts a signal onto the t-stat to tell it to open or close. I am not entirely sure how it works -- in the olden days, the t-stat worked entirely from the temp of the coolant, but there is an order of complexity to the one BMW is using that I have not learned about yet. Whatever the electrics are doing to the t-stat, one of the things they are doing is detecting the status of open of closed. Yours is detecting a constant open that might be false since your car maintains normal temps.

If you cheaped out and bought the bargain brand, then you might be fighting the t-stat and the processes that make it be the bargain brand.

37,000 miles on a 15-year old car? That's like 2500 miles per year. Nice find.
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Old 06-04-2015, 11:47 AM   #3
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Join Date: Sep 2009
Location: Madison, GA
Posts: 1,644
My Ride: E92 335 MT Coupe
Is the thermostat Behr or Wahler? Those are the two brands that I believe are OEM. I had two Wahlers before the SEL disappeared. I'd check the wiring harness and make sure that you don't have a short.
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Old 06-04-2015, 11:47 AM   #4
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Join Date: Nov 2009
Location: Fairfax, VA USA
Posts: 23,199
My Ride: 330CiC, M5, X5, E93
First put the Peake Reader away and do no use it on a regular basis.

Get an OBDII smart phone/tablet App and interface, typically $30 or less. These Apps support Emission Readiness Monitor Status, Freeze Frame and Live/Realtime data. They are also great for Logging data for review after the car has been driven and can really help find usual problems.

Android - Touch Scan for $3.95 and ELM327 OBDII to Bluetooth interface.

iProduct - OBD Fusion for $9.95 and ELM327 OBDII to Wifi interface.

Also read the 3rd & 4th link below in my signature.

The temp gauge is buffered in these cars over 40-50F range an it will always stay at 12 o'clock.

The engine temp should run about 96C.

The temp sensor in lower radiator hose has nothing to do with the engine temp.

We need to know what the temp is running and are you actually reading the Peake Reader correctly?

But as I said, put the Peake Reader away, it is pretty much a useless tool in my opinion.
Solve your misfires, lean codes, rough idle -

Fuel pump failures -

Temp Info -

Hidden OBC Menu - Check Voltage, Temp, Fuel Level -

E46/E39 GM5 Door Lock Info -

Lower hose temp switch O-ring - BMW #13621743299
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temp sensor, thermostat

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