Incorrect outside temperature reading

[JudgeM]

Hi all.

I am almost done with my instrument cluster swap.
I've noticed though the outside temperature reading is off. Its strange. It worked initially but now it doesnt work. it seems to be off by 10c. So when its 18c it shows 8c.

Its not the sensor because I changed it and still same problem, however if I wire the sensor directly to the meter, it shows the correct reading.

Any ideas on what I could check ? worst comes to worst I will just wire up an extra sensor directly to the meter, though I'd really like to avoid that.

Cheers

[CTScott]

If you go into the configuration section in Techstream for that ECU, I believe that there is a parameter that lets you adjust the offset. The problem is that you are reading the resistance of the AC ECU as well, so it throws the value off.

[JudgeM]

I had a play with Techstream last night. I did not find anyway to offset this setting. More worringly I think there is a problem with the AC ecu. I took some screenshots (see below) its obvious that the reading its getting is wrong when compared to the other sensors.

I am thinking the AC ecu is to blame. Do you think if I swap it out it could solve the problem ?

[CTScott]

I think the problem is that you have two devices now reading the ambient temperature sensor, so the voltage though the thermistor from one is effecting the other. It may be possible that the AC ECU for a car that has the cluster connected to the sensor relies on the cluster to supply the voltage through it, rather than competing with the cluster.

try disconnecting the AC ECU's connector and see if then the cluster reads it correctly.


On the temp offset adjust, I realized that that is only for some of the fancier new clusters that I have been working with (Prius, Camry Hybrid, Lexus hybrids).

[JudgeM]

CTscott you are spot on. I disconnected the AC ecu and it read correctly ! :bow:

So my question is now, can I just cut the thermistor wire that goes into the AC ECU and connect it to my meter instead ? I dont have the fancy climate control in my car, just the normal manual AC controls so I am thinking that the AC ecu doesn't really need to know the outside ambient temp.

[CTScott]

CTscott you are spot on. I disconnected the AC ecu and it read correctly ! :bow:

So my question is now, can I just cut the thermistor wire that goes into the AC ECU and connect it to my meter instead ? I dont have the fancy climate control in my car, just the normal manual AC controls so I am thinking that the AC ecu doesn't really need to know the outside ambient temp.

The manual AC ECU does want the ambient temperature input as well. I believe it uses it to determine the duty cycle for the compressor to avoid freezing the evaporator when running it for defogging in colder temperatures.

You can try it though as see how the AC works. Another option would be to connect a fixed value resistor to the AC ECU pin and fool it with a constant outside temp value.

[JudgeM]

I think the best thing to do is that I wire up another temp sensor for the meter alone.

I bought a spare temp sensor from the breakers anyway. This way I won't interfere with the original setup of the AC ecu.

Thanks CTscott for the information.

[JudgeM]

There is still a problem I saw when I put everything back together.

Techstream shows a fault in the AC ecu circuit ; Fault code B1412. I have removed the wiring from the meter to the AC ecu so there shouldn't be any problem. Any chance I may have damaged the AC ecu ?


See the images below:

[CTScott]

Measure the resistance on the pin for the sensor on the AC ECU connector, with the connector unplugged. Maybe you damaged the wire where you spliced it for the cluster?

[JudgeM]

I didn't splice the wire. I just squeezed it in the back of the crimp holder. However I suspect I may have accidentally put 12V through that sensor input.

I measured about 4k Ohm on the AC ECU across the sensor input pins.

[ojeysky]

Another option would be to connect a fixed value resistor to the AC ECU pin and fool it with a constant outside temp value.

Hello CTScott this is what happens in my case, i do not have the ambient sensor on but my scanner constantly reads that ambient temp is 81C, i wonder if 81 is a good value to have optimal coolness in the car. Outside temp is normally between 35 and 45C

[ojeysky]

Hello CTscot,

I got the sensor at Amazon (did a vehicle fit check on Amazon which passed before I ordered it) find attached picture but it doesn't seem to fit.
Is it possible that I am looking at the wrong place for the sensor?

Regards