engine coolant temperature sensors-M60 v8

[BMWross540]

Bentley Manual tells me that I can check the functioning by removing both sensor wires (M60) rear of engine in the coolant manifold. After disconnecting from sensors and connecting a jumper across both wire terminals, key on, then the Water Temp. Gauge should rise indicating that the sensors are good.

Query: at the stealership there are 2 separate part numbers for these sensors ( side by side on the manifold). are they different parts? how do they function then .....do they compare voltage and to what and why are there 2 of them-redundancy or what?
R

[mboor]

the 2 sensors are different. different part#'s and different functions, and different testing specs so they are calibrated different also. One is for the temp gauge on the dash (i think its the one closest to the drivers side of the car) and the other reads coolant temperature for the DME. They are basically a thermistor. A temperature regulated resistor. input voltage to the sensor is a constant 12 volts. the output voltage will vary depending on coolant temperature. The info is send back the the temperature gauge and moves the needle accordingly, or send to the DME where is it processed and used for fine tuning the engine management.

[SW530]

the 2 sensors are different. different part#'s and different functions, and different testing specs so they are calibrated different also. One is for the temp gauge on the dash (i think its the one closest to the drivers side of the car) and the other reads coolant temperature for the DME. They are basically a thermistor. A temperature regulated resistor. input voltage to the sensor is a constant 12 volts. the output voltage will vary depending on coolant temperature. The info is send back the the temperature gauge and moves the needle accordingly, or send to the DME where is it processed and used for fine tuning the engine management.

+1. And I can tell you from experience that getting the connectors crossed can cause issues. (big issues)

[BMWross540]

the 2 sensors are different. different part#'s and different functions, and different testing specs so they are calibrated different also. One is for the temp gauge on the dash (i think its the one closest to the drivers side of the car) and the other reads coolant temperature for the DME. They are basically a thermistor. A temperature regulated resistor. input voltage to the sensor is a constant 12 volts. the output voltage will vary depending on coolant temperature. The info is send back the the temperature gauge and moves the needle accordingly, or send to the DME where is it processed and used for fine tuning the engine management.

Thanks for current info good explanation . Not having pulled either cable to the sensor I assume each cable then is a 2 wire affair? The jumpering that occurs per the manual would be between the 2 wires of each cable?. Assuming drivers cable is to temp. gauge I understand gauge movement assures gauge operation and assumes sensor maybe faulty. what about quick check for passenger side (DME sensor)what does jumpering 2 wires in this cable do? Is gauge affected since this is input to DME and gauge is separate circuit??.

My system has extremely slow gauge response although it will eventually, only on a warm day get to mid scale? Winter days its always just off blue square at lower end of scale possibly indicating thermostat malfunction......... always open or missing ( haven't physically verified yet) or faulty temp sensor maybe car is overcooling?. This condition same since purchase from PO(no previous history)
I assume these to be small issue and thus not likely cables are switched causing big issues. How would I check to see if DME sensor is faulty ? car not run /or demonstrate issues I'm having? Is there an actual test for it ?(backprobe for 12 volts if hot?)
progress but not there yet
Ross

[mboor]

Sounds more like a stuck or missing thermostat then a malfunctioning sensor. Yes the gauge and corresponding sensor function separate from the DME. There is no communication between the two. There is a resistance value for each sensor, relative to temperature. If you can't find them on the internet I can get them for you Monday.

[excelsisba]

And they are color coded so you don't swap the plugs on accident.

[1994BMW540eye]

1994 E34. Can a bad coolant temp sensor prevent car from starting? That's what Bentley manual says at least. Over the last couple of months my machine has been increasingly hard to start especially in cool damp weather. Now it won't start at all. During this same period of hard starting, it runs just fine once it warms up a little. No problems with acceleration or higher speeds, so I'm thinking it is NOT fuel pump or fuel filter. Before this all started, had another sudden failure that resulted in O2 sensors and MAF being replaced, so I don't think it's that stuff. Is the temp sensor sending bad info to DME so that DME thinks car is warm when it is actually cold and then doesn't make the mixture rich enough to start?

[srad168]

Are the two connectors for the coolant sensors at the rear of the engine on passenger side the same?

[eddycooper]

They are not the same. As the post above mentioned, if you get them mixed up you'll have running issues. The sensors look very similar but they have different temperature/resistance curves. If you have aftermarket sensors they may not be colour-coded the same as the connectors like the OEM ones are.

[srad168]

Thanks. Will take a look into it.

[shogun]

12621710535 2-POL. M14x1.5, NTC-Sensor, engine temperature sensor, usually the color is black, Temperature Sending Unit (120 deg. C, 2-Pole) (Black Top), Cluster temp sensor
12621288158 2-pol ,M14X1,5 Temperature sensor, water, usually the color is white, (20 deg. C, 2500 Ohm.)

[a777fan]

I went through and replaced both sensors on my car this last summer. Unfortunately both sensors are now black in color, which makes them hard to tell apart at first glance.

They are, however, marked in a pretty obvious way if you look closer. On the 'nut' of the sensor you'll see a stamping if they are OE sensors. The DME sensor will be stamped 'Bosch' and the Cluster temp sensor will be stamped 'VDO'.



Ignore the fact that this Bosch sensor is white, its the old one. Forgot to take a picture of the new black one.



You can use the ETM to confirm that you have the correct wire colors hooked to each if you have lost track of which plug goes to which sensor. On mine, after figuring out which wires went where, I used a paint pen to mark one sensor connector pair to make it clear and less confusing in the future.

[srad168]

I looked at a pic before I removed. Black one is towards driver side, white one sits on passenger side.

[shogun]

Just discussing with a member about temperature sensors for DME and cluster, do not mix them up!
12621710535 usually black top, is a 5000 Ohm sensor, located towards driver side LHD car http://bmwfans.info/parts-catalog/E3...pipe#1710535_8 NTC 5kOhm at 25°C +/-2%, at 20 degree C. 6.200 Ohm
12621288158 usually white top, is a 2500 Ohm sensor , located more towards the fender side/passenger side LHD car, 20 deg. C, 2500 Ohm
both have threads M14x1.5, so if you mix these up, either the DME gets wrong info or the cluster shows a wrong temperature.

NTC 5kOhm
deg C............ohm
-30 88.700
-25 65.300
-20 48.500
-15 36.400
-10 27.600
-5 21.100
0 16.300
5 12,700
10 9.300
15 7.800
20 6.200
25 5.000
30 4.000
35 3.200
40 2.600
45 2.100
50 1.800

NTC 2500Ohm
deg C.....Ohm
-40 45.313
-30 26.113
-20 15.462
-10 9.397
0 5.896
10 3.792
20 2.500
30 1.707
40 1.175
50 834
60 596
70 436
80 323
90 243
100 187
110 144
120 113
130 89
coolant circuit diagram M60
MV1c0xr.jpg

[E34 Lives]

The two sensors are different, I replaced both temperature sensors when I did my valley pan as preventive maintenance since I was already there and it was very accessible.

The slow gauge sounds more like possible stuck thermostat. There seems to be different temperature thermostats available, one spec at 68C and I see another one spec with 88C, so depending on which one you have installed that might heat up at different rate.