1997 528i External Temperature Issue

[M3S52INGAround]

1997 BMW 528i. Issue: External temperature always reads -40.
Attempted Fixes: New Temp probe. New temp wiring harness and probe. Reversing the wires.
Main Issue: When it reads that cold outside, the heater is basically always on. We need it to read the correct temperature outside. After replacing the external temperature sensor, and harness on the passenger's side, the issue is still there.

Question: What else could it be that causes it to read -40?

Thank you for any information you can get me.

[Nyc Dito]

maybe a defective sensor? What brand or where did you buy it? Also, did you drive around and let it adjust?

[JimLev]

Check the sensor with an ohm meter.

[Dave Sal]

If the one you have proves to be defective, order one from FCP Euro. They have lifetime warranties on all their stuff.

[mattmar1]

by temp wiring harness, do you mean the connector or all the way from the probe to the cluster or just the connector end? just an fyi, the polarity of the wiring to the probe is of no issue, its just a simple NTC thermistor wired direct to the cluster. what brand OAT sensor did you use? a -40 reading means the system sees the sensor as an open circuit, as in there is no input or connection to the cluster. whenever you do anything with the thermistor, disconnect the battery for a few minutes then reconnect, the sensor is one of the infamous BMW buffered signals. youll then get a true current reading, not a saved one. and as JimLev stated, put an ohmmeter across the sensor and see what it reads, if its a nonsensical measurement or one within a reasonable range.

[cnn]

I recommend 2 things:

1. Relocate to a higher point so it is not damaged by the curb:

https://www.bimmerforums.com/forum/s...or-Replacement


2. Brand. I have used VEMO brand now for 8 yrs, zero issues.
PN 65816936953 at rmeuropean.com, about $7.50, best bang for your bucks.

https://www.rmeuropean.com/Products/...53-MFG400.aspx

[M3S52INGAround]

Sensor Type: APDTY 013131 Ambient Air Temp AAT Temperature Sensor With Wiring Harness & Connector Fits Select 1995-2011 BMW (View Vehicle List & Description; Replaces BMW 65-81-6-905-133, 65816905133 from Amazon
More Info: The sensor had been torn off before due to it's location. As cnn said, I relocated it to a more elevated position but still outside of the head of the engine compartment. It is now up inside the bumper area shielded behind the bumper core support.
The two wires for the temp sensor were hanging, the plug had been torn away. I cut into new copper, put both wires together and soldered them together.
Mattmar1 I think the above answered your question on how much I replaced. let me know.
I will strip away the shrink and get an ohm meter on it and see what it's reading, although I don't know what the typical reading should be.
Thank you everyone for your brand suggestions, I'll be looking into all of these tomorrow and I'll let you know what I find out when I test it.

Have a great evening.