Hi all - No, I don't live at the North Pole.

I'm looking for some help trouble shooting my external temperature. The car never had any problems until I went in and had the air conditioner serviced about 9 months ago. When I go the car back the outside temp was showing -22... basically indicating no connection. I popped the hood and found one of the plugs disconnected down near the input for the refrigerant. I plugged it in, and not immediately, but shortly thereafter the temperature re-appeared. For the past 9 months or so, sporadically the temp gague will read the -22 degree readout. When I installed the front mount intercooler, I went ahead and replaced the sensor with a new one, assuming that might be the problem. It wasn't. I have no idea what's causing, it. Fast forward to about 2 weeks ago. I was adding some refrigerant to the system and since then, the -22 has become a permanent figure on the readout. So I'm trying to figure out how or why that might be? Some refrigerant did spray out, and no doubt it got on the temp sensor itself. However, I'd be shocked if this kills temperature sensors.

The other night, I did some diagnostics. This is where I need some help. I first ran a continuity test on the harness that plugs into the temperature sensor. The readout indicated an open loop, no reading/resistance could be found. Then I turned the key on, and tested the harness again for any 12v signal. None existed. So I'm suspicious that my problem might be that somehow the harness has gotten pinched and or otherwise damaged where there is no longer signal coming to the sensor itself. If someone knows that I should be getting voltage at the sensor through the harness (I have to assume so, right) could you confirm this for me? Is there any other sensor within the system that could be faulty and therefore preventing a 12v signal from running to the temp sensor?

To keep with my theme of pictures being necessary for good discussion, here are the parts in question:

 

Scan Tool Check:
Lexus wants you to hook up a scan tool first and see if the Ambient Temperature is correct on the HVAC data list. If it's good here the AC control assembly is most likely shot. If not they continue on to the voltage and resistance tests. Of course, you will need access to a scan tool with HVAC system support to do this part.

Voltage Test:
Turn ignition switch ON. Measure voltage between terminals TAM and E2 of ECM connector at each temperature.

at 25°C (77°F): 1.35 - 1.75 V
at 40°C (104°F): 0.85 - 1.25 V

As the temperature increases, the voltage decreases.




Sensor Resistance Test:
Disconnect ambient temperature sensor connector. Measure resistance between terminals 1 and 2 of ambient temperature sensor connector at each temperature.

at 25°C (77°F): 1.6 - 1.8 kohm
at 50°C (122°F): 0.5 - 0.7 kohm

As the temperature increases, the resistance decreases. When installing the ambient temperature sensor, be sure to connect the sensor connector before connecting the battery.

 

The reading is the default reading . Most likely you have an open circuit. the ecm is not seeing the sensor. disconnect the battery and use your ohm meter and check for continuity in the wire from the sensor to the ecm. First perform resistance test of the temp sensor.

 

You r getting frustrated .You have the tool use it the right way. forget voltage at this point. the connector has two terminals ,perform the conitnuity test with one terminal at a time to the computer. Once you do that you would know whats your problem. If you have an open on one of the wire ,start checking smaller section at a time until you find it. If there is no open then you may have a bad amplifier.(A/C). let me know how you make out.