So, I get in my week old 2006 Dodge and the temp reads -40. WTF! I traded in my 2001 and it did the same thing. I unplugged the sensor under the hood, made sure it was clean and plugged it back in. When dis-connected, it threw a CEL. I cleared it, but it then read -29. After I drove for like 15 minutes it slowly came back. Any ideas where to start?

 

AMBIENT TEMP SENSOR DESCRIPTION

Ambient air temperature is monitored by the overhead console. The ambient temperature messages are received from the Front Control Module (FCM) over the Programmable Communications Interface (PCI) J1850 data bus circuit. The FCM receives a hard
wired input from the ambient temperature sensor (Fig. 7). The ambient temperature sensor is a variable resistor mounted to the underside of the hood, in the engine compartment. For more information on the front control module, refer to Front Control Module in the Electronic Control Modules section of this manual. For complete
circuit diagrams, refer to Wiring. The ambient temperature sensor cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

OPERATION

The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal sent to it by the Front Control Module. The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage
to the Front Control Module. Based upon the resistance in the sensor, the Front Control Module senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature. The Front Control Module
then sends the proper ambient temperature messages to the EVIC, CMTC over the PCI J1850 data bus.

The temperature function is supported by the ambient temperature sensor, a wiring circuit, the Front Control Module, the Programmable Communications Interface (PCI) data bus, and a portion of the Electronics module. If any portion of the ambient temperature sensor circuit fails, the Front Control Module will self-diagnose the circuit.

For complete circuit diagrams, refer to Wiring.

DIAGNOSIS AND TESTING - AMBIENT TEMPERATURE SENSOR

(1) Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. Disconnect the ambient temperature sensor wire harness connector.
(2) Measure the resistance of the ambient temperature sensor. At 24° C (75° F), the sensor resistance should be approximately 10.3 kilohms. At 30° C (86° F), the sensor resistance should be approximately 7.57 kilohms. The sensor resistance should decrease
as the temperature rises. If OK, refer to Diagnosis and Testing - Ambient Temperature Sensor Circuit in this group. If not OK, replace the faulty ambient temperature sensor.
NOTE: The ambient temperature sensor is a very sensitive device. When testing, be certain the temperature sensor has had time to stabilize (room temperature) before attempting to read the sensor resistance. Failure to let the ambient temperature
sensor temperature stabilize could result in a misleading test.

DIAGNOSIS AND TESTING - AMBIENT TEMPERATURE SENSOR CIRCUIT

(1) Turn the ignition switch to the Off position. Disconnect and isolate the battery negative cable. Disconnect the ambient temperature sensor wire harness connector and the Front Control Module wire harness connector.
(2) Connect a jumper wire between the two terminals of the ambient temperature sensor wire harness connector.
(3) Check for continuity between the sensor return circuit and the ambient temperature sensor signal circuit cavities of the Front Control Module wire harness connector. There should be continuity. If OK, go to Step 4. If not OK, repair the open sensor return or
signal circuit as required.
(4) Remove the jumper wire from the ambient temperature sensor wire harness connector. Check for continuity between the sensor return circuit cavity of the Front Control Module wire harness connector and a good ground. There should be no continuity. If OK, go to Step 5. If not OK, repair the shorted sensor return circuit as required.
(5) Check for continuity between the ambient temperature sensor signal circuit cavity of the Front Control Module wire harness connector and a good ground. There should be no continuity. If OK, refer to Diagnosis and Testing - Overhead Console in this group. If not OK, repair the shorted ambient temperature sensor signal circuit as required.

REMOVAL

(1) Open the hood.
(2) Disconnect and isolate the battery negative cable.
(3) Working on the underside of the hood, remove screw holding sensor to hood panel.
(4) Disconnect the sensor electrical connector and remove sensor from vehicle.

INSTALLATION

(1) Connect the sensor electrical connector.
(2) Working on the underside of the hood, install screw holding sensor to hood panel.
(3) Connect the battery negative cable.
(4) Close the hood.

 

like weedahoe said, its your ambient temp sensor that reads the temp in the overhead counsole.
The sensor is located on the lower bolt of your left headlamp. If i remember right

It is either shorted or open thats making it read its default temp of -40*
I think a short to ground will make it read that.

 

Yeah, Ive read up on this before, I think the short makes it read -40 and an open circuit reads 130*

 

i think open circuit goes to 113* i may be wrong though. anyways it doesnt matter.
i would look into there being a short

 

left=driverside..fyi

 

I know where its located, I disconnected it to check if the conneciton was dirty ect. When I pulled it, the truck threw a CEL. Odd that happened.

I dont know where to start looking for a short, other than testing the actual sensor itself.

 

See if this helps