krzyschicago

Dear Fellas, here is my sad story....

Few weeks ago my 545i had been involved in a minor collision. Nothing major, front bumper, grill, rebar etc. Car has been fixed, but since the accident I cannot get rid of P0128 code.

Car does not reach operating temp now, averaging around 84 degrees C on HWY. When in traffic, temp goes temporarily up to 90 but, when I pick up speed it goes down again to 83-84

I read a code with portable reader, and narrowed the problem down to thermostat, coolant temp sensor, or intake air temperature (IAT).

I am ok with replacing thermo&coolant sensor (probably will replace water pump as well), but can anyone confirm what "intake air temperature (IAT) sensor" is? Where is it located, or provide BMW part #? When googgled, I am getting pics of ambient temperature sensors. On the other hand, I do remember temperature sensor hanging on a wire right after the accident, but supposedly it was fixed/replaced, and also outside temp readings seem to be ok.

Does IAT sensor = ambient temperature sensor in 545i??

In addition, I suspect that maybe I am missing some parts after a repair. I can swear that right after an accident there was a black piece of plastic laying on a splash shield in the bottom, under the radiator. I recall it as rectangle, maybe 2.5 x 12 inches with something like a sensor connected to it on a right side. The problem is that, before my new bumper was installed, I looked everywhere and could not find it anywhere!!!! I checked Realoem, TIS'es and still have no clue what was that. Body shop say there is nothing missing. Maybe that was the IAT sensor, and they just did not install it?

Does anyone have a slightest idea what possibly was that??

Or someone, provide some close ups pics of E60 (preferably 545) without front bumper? I assume this part was located in front of the radiator, possibly by power steering cooler or higher. Sorry, for asking stupid questions, but I am desperate. I love the car, and I am fu$% sick, when I see "check engine" light on.

Please advise if anyone can shed some light... Thank you in advance!

As stated in a topic line, I offer reward - free case of beer to anyone who can help. No shipping - local pickup in Chicagoland only though

pcy

There's an ambient temp sensor mounted on the inner part of the bumper almost at the center of bumper. It can be seen when you sit in front of the front bumper (at the center of bumper) and look straight towards the radiator. It's mounted on the bottom and it's pointed up.

krzyschicago

Thanks for the reply. This is an ambient temperature sensor. But is it the same as intake air temperature sensor in these cars?

pcy

Idle Air Temp sensor is integrated as part of Mass Air Flow Sensor (MAF). As the air is passing thru the MAF, it measures the volume of the air passing as well as the temp of the air.

rgb129

What exactly did the code reader say?

rgb129

Nevermind, I looked it up:

I am guessing it is thermostat or the coolant sensor. The IAT is part of the MAF and you'd have other problems if those weren't working. It is also would not have been in the danger zone of your accident.

krzyschicago

Thanks for the reply. So, I am not missing IAT I am going to focus on coolant sensors (as far as I know there is one on a water pump and one on radiator hose), and thermostat. However, both are located too far from the impact, so unless it is a coincidence that impact triggered this error, I may still be missing some parts...

donpb

Get someone to read the fault codes for you.

krzyschicago

I did. The code on Autozone scanner was P0128. Would INPA or something give more specific code?

BimmerFan52

P0128 code is almost always an indication that the heater coil in the thermostat has burned out.

Some modern cars, including the 545i, have a thermostat with the heater coil, which allows the cars engine control computer to accelerate the opening of the thermostat by supplying a voltage to this coil and accelerating the melting of the wax which physically opens the thermostat and allows the flow of coolant.

It is easy to check. Remove the electrical harness that connects to the thermostat and using a multimeter, measure the resistance between the two brass conductors exposed when the harness is removed. If the coil is intact it should measure around 16ohms. If the coil is burned out it will measure 1. The coil is tested each time the engine is started to ensure it is present, and if the connection is broken the computer generates the P0128 code. The thermostat will still work fine, so there is no urgent rush to replace it, but if the engine is driven hard before fully warmed up (not a smart thing to do anyway) the computer will not be open to quickly open the thermostat.

If the coil is intact you can continue your search elsewhere.