New temp sensor and plug, car still reads -40F

[BoardEm]

The splash panel that had the sensor broke and the sensor and plug were pulled off by a snow bank here in the normally snow free Southeast VA. Anyway, I ordered the repair kit and a new plug from BavAuto and hooked it up. I wanted to solder the wires together rather than use the crimps for a better connection. Before it joined them permanently, I twisted them together to make sure it was working. When I did this the temperature still read -40. After some reading, I saw people saying it takes time to register and I went ahead an soldered them hoping it would work. Well, two weeks later I'm still seeing -40 and it's 60 outside and my heat is blowing on the climate control even though that's down to 65. Any ideas where I can go from here? Would it help to measure the voltage on the wires? What should it read? Thanks for any help.


Also, anyone who has used the BavAuto repair kit, how far do you need to push the wire with the plug things on them up into the plug itself? I pushed them in there until they wouldn't come back out and it doesn't seem like it would go farther but I didn't try to force it. I didn't want to break it.

[cal45fan]

Check upline and investigate the extent of the damage. Good luck.

[NNY528I]

do you have the leads reversed? Not sure if that might cause it but it might.

[cnn]

Polarity of the circuit not important.
The temp sensor is simply a resistor working on NTC principle.

[SpeedsterBek]

Check with a voltmeter to see if you're getting power. I bet the wire is broken internally somewhere in the upline.

[NNY528I]

Polarity of the circuit not important.
The temp sensor is simply a resistor working on NTC principle.

Actually if it is a thermocouple then polarity does matter depending on the type of thermocouple used, I do not know the exact design of that sensor.

[BoardEm]

I looked up at it as best I could and didn't see anything wrong with the wires. I'll check again. Friggin' snow. Now it's getting warm and I'm burning up with the damn heat running.

Actually if it is a thermocouple then polarity does matter depending on the type of thermocouple used, I do not know the exact design of that sensor.

I tried it both ways before soldering and neither worked.

[mattmartindrift]

have you disconnected the neg. battery terminal? I had to do that before mine would work, not really sure why.

[netstat]

hi,

I had the same issue on my 1997 528i and simply connecting it was not enough. You have to short the terminals for the sensor to be "accepted". In other words, connect both the terminals to the sensor, get another small piece of wire and while ignition is in postion 1, short the sensor terminals together. You will see the reading from -40F change to the actual one.

I am not sure if this is the recommended way, but it worked for me.

[BoardEm]

have you disconnected the neg. battery terminal? I had to do that before mine would work, not really sure why.

No. But I'm going to try that too. At the time I didn't want to reset my gas mileage counter (I was trying something out to get a little better mileage on trips).

hi,

I had the same issue on my 1997 528i and simply connecting it was not enough. You have to short the terminals for the sensor to be "accepted". In other words, connect both the terminals to the sensor, get another small piece of wire and while ignition is in postion 1, short the sensor terminals together. You will see the reading from -40F change to the actual one.

I am not sure if this is the recommended way, but it worked for me.

Nothing seems right about this. Which means it probably works.

[boondocksaint]

I looked up at it as best I could and didn't see anything wrong with the wires. I'll check again. Friggin' snow. Now it's getting warm and I'm burning up with the damn heat running.

Wait, why would the heat be running because of the outboard temp sensor? AFAIK the only thing that affects is the heated mirrors and the REST function of certain climate control systems (maybe that's an E38 thing though). The internal climate control system has its own temp sensors.

What am I missing?

[eva89]

Netstat is correct - you need to short the terminals to calibrate the sensor. I had to do the same thing. With the car off, bend a piece of wire into a "u" shape, and short across both terminals. After it is in place, turn the key to the "on" position, while still on, remove the wire and plug in the sensor. Check the display, the temp should then be correct. Also, the climate control will not work right if the temperature is reading -40.

[Arucano]

When the external temperature sensor "tells" the car it is very cold outside, it will turn on the heat in "anticipation". I had the same thing happen wen I damaged my sensor coming back from O'fest a few years ago. I did not have to do any "resetting" when I replaced the sensor however.

Regards

Wait, why would the heat be running because of the outboard temp sensor? AFAIK the only thing that affects is the heated mirrors and the REST function of certain climate control systems (maybe that's an E38 thing though). The internal climate control system has its own temp sensors.

What am I missing?

[Qsilver7]

Wait, why would the heat be running because of the outboard temp sensor? AFAIK the only thing that affects is the heated mirrors and the REST function of certain climate control systems (maybe that's an E38 thing though). The internal climate control system has its own temp sensors.

What am I missing?

The ambient temp sensor's data does affect the IHKA panel. It receives the data from the temp sensor by way of the ECU...and when ambient temps are BELOW +41 °F...the AC compressor does NOT operate (which dehumidifies the air and makes it feel cooler).

So if the ambient temp sensor is reading -40 °F ...it can make the HVAC system work hard (if possible at all) to cool the cabin.

Also, the "values" (warmed air vs cooled air) configured to keep the interior temp setting varies depending on if it is -40 °F versus the ambient temp being +60 °F.

[BoardEm]

Netstat is correct - you need to short the terminals to calibrate the sensor. I had to do the same thing. With the car off, bend a piece of wire into a "u" shape, and short across both terminals. After it is in place, turn the key to the "on" position, while still on, remove the wire and plug in the sensor. Check the display, the temp should then be correct. Also, the climate control will not work right if the temperature is reading -40.

I'll try it after I disconnect the battery. It sucks with the freaking car thinking it's -40 and it's trying to warm the cabin when it's 70 outside.

[ArmySweitzer]

mine took a few days to start working fwiw.

[jamesdc4]

So if the ambient temp sensor is reading -40 °F ...it can make the HVAC system work hard (if possible at all) to WARM the cabin.

*fixed*

[boondocksaint]

God I hope mine is one of the easy ones to fix, then. My sensor is gone, as is the underpanel that held it in place. Gotta find out how much wire is even left under there.

[ArmySweitzer]

*fixed*

i heard it was tied into the air conditioning system and wouldn't blow cold air thinking it was quite cold outside.

[BoardEm]

mine took a few days to start working fwiw.

I thought this might be the case too but it's been two weeks. I'm going to try the battery then shorting the wires. If that doesn't work I'll just roast with the heat blowing this summer.

[jmedarts]

I bought the kit from Bavauto and had the same issue.

It's been a while, but I think the sensor itself comes as one piece but it is actually two, and you have to take the inserted piece out, and then open it up, in order to get the connector ends of the supplied wires all the way into it.

Carefully examine it and you will see where it comes apart. I almost felt like I was breaking it. The connectors on the ends of the wires end up all the way at the end of the plastic male piece when they are inserted properly, then the male piece goes into the female temp sensor itself.

I then just crimped the wires onto the leads. According to "bavarian otto" the polarity is not important.

Good Luck

[BoardEm]

Fixed. The female plug Bav Auto provides is three pieces; a gray piece, a green piece, and a white piece. I pulled them all apart and once I too the white piece off the wires simply slipped in. Simple instructions saying to take all the pieces apart would have saved me a lot of time and cussing. Oh well. Thanks for the help.

[mattmartindrift]

glad you got it working! we all need to throw a few tallies in the win column with our e39 electrical endeavors

[BoardEm]

glad you got it working! we all need to throw a few tallies in the win column with our e39 electrical endeavors

Now if I could just figure out my weird clock and brake light problems from a few months ago you tried to help me with, all would be good.

[jmedarts]

Fixed. The female plug Bav Auto provides is three pieces; a gray piece, a green piece, and a white piece. I pulled them all apart and once I too the white piece off the wires simply slipped in. Simple instructions saying to take all the pieces apart would have saved me a lot of time and cussing. Oh well. Thanks for the help.

I think I still have the email exchange with bavarian otto in which I made the same suggestion. I understand it's expensive to have something printed and inserted with the part, but put the instructions on your site. They have all sorts of great illustrated jobs in their newsletters, seems like this would be an easy addition. Tearing apart that wheel well cover is a dirty pain in the butt job that you really only want to do once.

When mine goes again (I'm on my third one now) I will take pics and make a DIY link.

[I should add this is the ONLY complaint I have with bavauto. Good prices, nice people, great service, & stuff arrives really quick here in CT]