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Go Back   E46Fanatics > Tuning & Tech > Driveline, Engine & DME Tuning

Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 12-10-2014, 02:11 PM   #1
jared_wiesner
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Join Date: Aug 2009
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My Ride: 1999 328i (M54b30)
Engine Coolant Temp Sensor Question

Does anyone know what the failure mode of the temp sensor at the back of the cylinder head is?

From doing some reading people are suggesting it sends two signals, one to the temp gauge and one to the computer.

My vehicle has been having trouble with cold starts and I'm trying to decide if it's tune related or if it could be that this sensor has failed.

My temp gauge works normally and ECT when data logged from cold to hot is normal.
I have no codes and up to this point I did not suspect any issues with my coolant temp sensor.

That was until I started reading posts by some people suggesting that it sends out two signals. Is there some second signal the DME is supposed to get for deciding on cold start maps, etc. that I wouldn't see by a malfunctioning coolant temp gauge or for that matter the data logged ECT readings?

I think I may have re-used the coolant sensor in my replacement engine rather than swapping the known working one out of my old motor, that is also what makes me unsure of its history.
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Old 12-10-2014, 03:21 PM   #2
daniel_f.
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There are 2 coolant temp sensors on our M54 engines. One should be close to the radiator and one at the cylinder head. The one at the head should be called tco_ex in the damos and is used several times. I tend to think you could check that sensor by switching the tco_ex config switch off. European Z3 doesn´t have that sensor at all.
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Old 12-10-2014, 03:26 PM   #3
jared_wiesner
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Quote:
Originally Posted by daniel_f. View Post
There are 2 coolant temp sensors on our M54 engines. One should be close to the radiator and one at the cylinder head. The one at the head should be called tco_ex in the damos and is used several times. I tend to think you could check that sensor by switching the tco_ex config switch off. European Z3 doesn´t have that sensor at all.
Hmm interesting,

As far as I was aware the only function of the one on the lower radiator outlet hose was for switching the electric fan.

What I've been hearing is that the one in the cylinder head sends two separate signals.
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Old 12-10-2014, 04:17 PM   #4
jared_wiesner
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I dunno reviewing pictures of that sensor and it only has a two prong connection, I'm thinking it can't possibly send two signals. If my coolant temp is correct it must be working.
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Old 12-11-2014, 02:14 PM   #5
sonny1985
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My Ride: E39 523iM52TU
Hi

Its the Same Sensor on my M52 TU

The Sensor in the Cylinder Head (Shitty to Remove... ...),It has 4 Pins , Is for Engine Coolant Temperature (DME ECU), AND (!) For Temperature Gauge at IKE/KMB (Instrument cluster)
BUT: If it shows "temperature" in the Cluster, that does NOT Mean, that the DME Gets a Correct Signal. Its a Kind of 2 Sensors in One Sensor *lol*

http://de.bmwfans.info/parts-catalog...tached_parts//
Part 3 - Dual Temperature Sensor (Same shit on x23-x28 M52TU - M54 ...)

The Auxiliary Fan, is switched BY THE DME. PWM Signal.
(PWM Controller on the Fan Directly)

The Sensor on the WaterTube, (in front of Radiator), its called "temperaturfühler Kühleraustritt" (German), (Temperature of Coolant that comes OUT from the Radiator)
DME Needs it FOR PWM'ing the Fan .
And the IHKA needs this Signal (Climate Control) too
http://de.bmwfans.info/parts-catalog...m_water_hoses/
Part 4
Greetings from Austria

Here the DUAL TEMPERATURE SWITCH:
Dont Get Nervous, because you see 2 Wires. - In the Car, you have 4 2 DME, 2 KMB

Last edited by sonny1985; 12-11-2014 at 02:24 PM.
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Old 12-11-2014, 02:26 PM   #6
sonny1985
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I Mean the Round connector on the sensor, has 4 pins, (Sensor logically too .
but in this picture you only see a experiment (maybe)
sry for Bad english ... ^^
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Old 12-11-2014, 03:25 PM   #7
jared_wiesner
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Thanks for all the info sonny! Your english is just fine.

So if the sensor somehow outputs two signals and the one the DME uses for cold starts etc is bad, how would you know this?

Is this what you would see as the engine coolant temp when data logging or is it another value that you would not know about?

I guess what I'm after is whether the engine coolant temp data is taken from the signal given to the gauge or whether it is what the dme is seeing as the second signal.
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Old 12-11-2014, 05:26 PM   #8
jared_wiesner
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Ok, Just got a chance to look at my old engine. The temp sensor in it was only turned in a few threads which tells me I must have taken my old one and swapped it into the new engine.

It was working before and I'm sure it's working now, must be the tune.
If anyone has any further info on diagnosing a bad temp sensor feel free to share.

I'm sure it will benefit someone in the future.
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Old 12-12-2014, 01:20 AM   #9
daniel_f.
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You could try to find comparable resistance measurements and compare them Measure at 0°C and in boiling water should give you an idea if the sensor is gone or good.
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