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15yearsaturnguy
15yearsaturnguy, Saturn master tech
Category: Saturn
Satisfied Customers: 1918
Experience:  25 years automotive experience, 15 years with Saturn
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2007 Saturn Ion: temp gauge signal..sending unit..instrument cluster

Customer Question

My 2007 Saturn Ion keeps loosing it's temp gauge signal and the AC quits working. I have changed the sending unit replaced the computer and reprogramed it also replaced the instrument cluster. When the problem happens, I can remove the negative from the battery and the gauge and the AC works. I am out of answers.
Submitted: 5 years ago.
Category: Saturn
Expert:  15yearsaturnguy replied 5 years ago.

15yearsaturnguy :

Hello and thank you for your post. I am a master certified GM tech, with 15 years Saturn experience,and can help you to resolve your issue.

15yearsaturnguy :

which computer did you replace? the engine or the body control module? (ecm or bcm)

15yearsaturnguy :

have you installed a scan tool to read engine coolant temp as it is being reported by the sensor?

15yearsaturnguy :

I believe at this point that is your only option moving forward.

15yearsaturnguy :

if you do not have access to one, it is time to take this to a mechanic and see if the sensor is reporting properly when the gage goes off

Customer:

I replaced the ECM and I have a scan tool but if there are no codes to read the check engine light is out. I will look at the BCM to see what is going on there.

15yearsaturnguy :

the ecm gets the coolant temp signal from the sensor and then sends a signal to the cluster and to the body control module which also communicates with the cluster

15yearsaturnguy :

according to my info, the bcm is not in the loop for the coolant gage but i doubt that is correct as the bcm really controls almost everything on this car

15yearsaturnguy :

so you MIGHT have a bcm issue but I can't say

15yearsaturnguy :

on your scan tool, read the coolant temp sensor reading when the gage is reading badly and if the coolant temp reading is also bad then you have an issue with the sensor or the wiring

Customer:

Let me check this out and will talk later

15yearsaturnguy :

tip: if the sensor reads about-40F then it has an open wire

15yearsaturnguy :

if it reads about 290F then you have a short to ground across the signal return wire.

15yearsaturnguy :

so check that and let me know what you find

Customer:

ok

15yearsaturnguy :

good luck

Customer:

The problem was the Themostat it was bad and the computer was setting a fault code of dropping out at 174 degrees. The dealer had to find the problem. It was not the gauge computers or anything wiring related.

15yearsaturnguy :

ok. glad you got it figured out.

15yearsaturnguy :

as I said before using a scan tool was required to solve this. ( to see what the temperature was being reported by the sensor)

Customer:

I have a scan tool it was not showing the fault. What they did was hook it upto a laptop and watched it work. That's when they figured out that the thermostat was bad. My regular scan tool did not show this message and he informed me it wouldn't.

15yearsaturnguy : Ok I am Just glad it's fixed
Customer:

Thanks, XXXXX XXXXX to be a bigg issue with Saturns he said. The Ion, Sky and the Vue

15yearsaturnguy : I have not really seen any thermostats fail in this way but if he has then he may be on to something