Hi Everyone,

I have an issue with chevy impala 2017. The ambient air temp displays -40 C and from what I read it need sensor replacement. I replaced it and still got -40 even after a week of daily driving which should be enough to update the reading. I searched everywhere for info about the output of the sensor socket from the main ECU and if it does output 5v or nothing at all to confirm if the problem is from the wiring.
Mine output 0 volts at output of socket but I am not sure if this is normal or not. Hope someone could help.
* I know for sensors that has 3 wires there is ground / 5v / signal but this ambient sensor is 2 wire only.

Thank you very much

 

-40 indicates either the sensor or wiring is open. if you remove the connector at the sensor and jump the 2 wires together the sensor should read the max hot temp...if it doesn't the wiring is probably open.
iirc the cluster sends voltage out to the sensor on the blue gray wire at key in run. if you have no voltage you either have a broken wire or bad cluster. most likely a broken wire. I would inspect the wiring at locations that are exposed to road debris or where is passes thru a body part. if you can't find the break but confirm no power out from the cluster...run a new wire from the cluster to sensor.

 

Thank you so much for the fast and elaborate answer. I did try couple of 1k- 5k ohm resistors and even shorted the terminal and nothing changed on the readings so I guess it is broken wire. Does the wire run from cluster or from the HVAC module itself?

Thanks

 

cluster....... then the data is sent via data bus to other modules ie auto hvac

 

I had the issue with my 2016 Impala that my dash would read -40. Tested the sensor for ohms resistance. Added heat and the resistance went down, so I knew it was ok. To sum it up, here is how the system works. The instrument cluster sends 5 volts through the blue/grey stripe wire to the sensor behind the grill. The blak/blue stripe wire returns the reduced voltage to the cluster and the computer calculates the temp from that. If your sensor is good then the next step is to check if you have 5 volts at the nose harness by testing the blue/grey wire to ground. If no voltage then you must move on to remove your cluster(i know its a pain in the butt) and check the 32 pin harness. Pin 27 sends the voltage and it is returned on pin 25. I first checked for continuity between the cluster harness and the sensor harness, check each wire separately. I did not have continuity on either. I then stripped a small part of the wire sheething on the blue/grey wire, hooked up the cluster, turned the ignition on and tested the wire to ground. In this case the cluster was putting out the 5V. That confirmed the wares were compramised between the cluster harners and the sensor harness. I spliced in two new wires, ran them through the firewall to the nose and spliced in the ambient temp harness. Wrapp all connections tighly and it now works. Not entirely sure how the original wires wen bad, but this was the next best fix. Hope this helps