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BMW Check Engine or Service Engine Soon Light – Thermostat Fault Code

November 12, 2010

This answer is applicable for many BMWs in addition to the one listed below.

Q
car year: 2004
car model: 325Xi
Last month, I noticed the service engine light came on when I was driving. It did not go away the next few times I drove it. So, I ordered a diagnostic kit (fault code reader/reset tool) from your catalog. While waiting on the kit to arrive, I took my car on a short trip and I noticed the light had gone off. When the part arrived, I did the check and got the fault code for thermostat. Does the light going off indicate that It was only an intermittent problem? I’ve been told that thermostats sometimes stick.

A
The thermostats in late model BMWs (most models 1999 and later) are electrically controlled. When the signals through the thermostat circuit are not what the engine management system expects to see, it will generate a fault code (even if the temp gauge seems to read as it should). Often the fault light will go out, but the code is still there. You likely do need to replace your thermostat (thermostat failures are very common). If you want to check this, to be sure, check the current fault codes (record them) then clear the codes and see if the same fault codes return. If they do, then you need to address whatever issues apply to the faults (such as the thermostat).

Thermostats:

Fault Code reader & reset tools:

2 Comments
  1. Greg Goldstein permalink

    I have a warning light lit in my 2006 BMW E90 320i sedan. The car has done 60k km and I have noticed no problem in the way it handles. The warning is the engine symbol. The manual states this symbol has a different meaning depending on where it is located (either in “panel 1″ or in “display 2″ areas of the instrument panel), whether it is yellow or red, and whether or not it is flashing. In my case, its yellow, its in panel 1 and its not flashing. The manual says the cause is “engine fault with adverse effect on exhaust emissions”.
    I would appreciate any advice or information about this error.

    • The light is indicating that a fault code has been stored. The only way to know what the code (or the fault) is, is to read the code with a code reader tool, as noted in the original post.

      Click the link for the code reader tool, in the post above.

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