Check engine light

Ok… This is really starting to get annoying. I have 328i 1998 E36 when I first bought it the check engine light would stay on all of the time; finally
I got the dealer to fix it, after many trial and errors of finding the problem. They replaced all of the cats. And then the O2 sensors. The light final stopped coming on. Last week I change the oil, plugs, air filter, fuel filter, and used my code/reset tool to rest the oil light. The problem is today and yesterday when I got up it was below freezing, the OBC came on to let me know when I started my car, it did this kind of weird revving warm-up for about three seconds then stopped. Today it did the same thing, but in about three minutes of driving the check engine light came on. I am going to check to see what code I get later today. Any one have any idea why this would happen?
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No, but when you get the code read let us know. We may be able to help figure it out.
Kyle. 98 740iL 01 525i
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Ok so I read the code on a peake research R5/FCX-2 . The code was--Time to close loop temperature too long-- What the heck dose that mean??? I reed some where that it might mean i need a new thermasta. I was planing on doing a radiator flush this weekend, should i change it then... Or should I just wait to see if it happens again?
Kyle and Lori Greene wrote:

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It sounds like a bad t-stat. The emissions and fuel system runs in what's called open loop (a set group of engine parameters) until it warms up. Then it goes into closed loop where the O2 sensors control the mix. This link may show you what you need to know... http://stealth316.com/misc/obdii_fuel_trim.pdf
Kyle. 98 740iL 01 525i
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Jesse via CarKB.com wrote:

That won't help. The error is talking about the time for the O2 sensor to achieve closed loop temperature. It will eventually reach that temperature from the exhaust gas, but there is supposed to be a heater element inside the O2 sensor to help get it up to temp faster. The heater element can't be burnt out or that would throw a different code, so moist likely the relay that is used to supply the voltage to the heater is FUBAR. Find some wiring diagrams, break out the multimeter and check it out!! It should have heater voltage when you first start the car.
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Which O2 sensor? All of them or just one? Is it worth fixing? The code did not come back on today, and it is only cold in AZ for about a month? I did notice this morning on the way to work (15 min drive) the the temp gauge barely came out of the blue. Malt_Hound wrote:

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Jesse via CarKB.com wrote:

Just the forward one. The 2nd O2 sensor is only used as a check that the cat is functioniong normally. It is not in the fuel injection closed loop

Sure it's worth fixing. Otherwise when you get another check engine light that may be significant you'll think it is just this again...

15 mins is probably not long enough. I'd run the car for a bit longer and make sure it does fully come up to temp. If nbot, that may be worth pursuing first even though they shouyld be unrelated to the code that you mentioned.
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The O2 Sensor has to come to temp within a certain period of time, it's taking too long.

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Your car is OBD II (On Board Diagnostics, Level 2) compliant, this means that there is a diagnostic port along the bottom edge of the dash board that you can plug a code reader into, and the car will tell you (almost ) precisely where the problem is. I said "(almost)" because there can be multiple codes that are all rooted in a particular component -- a kind of ripple effect -- and sometimes there is a wiring problem to the component rather than a component failure. In any case, anybody that throws a box full of parts at a car anymore in hopes of shot-gunning a solution is probably a mechanic that one should stop seeing.
(Shot-gunning is a term that comes from the idea of a shot gun, shere hundreds of pieces of shot leave the barrel, but only one piece is needed to actually kill the bird.)

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