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Mike S.
Mike S., ASE Certified Technician
Category: Cadillac
Satisfied Customers: 7568
Experience:  ASE certified
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2009 cadillac DTS. I have proper voltage on my water temp

Customer Question

2009 cadillac DTS. I have proper voltage on my water temp sensor wire when warmed up it drops from 4.9 to 2 volts but my gauge doesn't work. It does move when the engine is started
Submitted: 1 year ago.
Category: Cadillac
Expert:  Mike S. replied 1 year ago.

What does the temperature gauge read with the engine off/cold, key on/engine cold and finally key on, engine warm?

Expert:  Mike S. replied 1 year ago.

Also, I need the 8th digit of your vin number so I know which engine this is.

Customer: replied 1 year ago.
It reads the same all the time. It reads at the bottom of the scale. The only time it moves is when the car is first started were it goes all the way to the top and then back down to the bottom of the scale. My sensor voltage at my temp sensor is slowly rising as the car cools down, it is at 3 volts now. Mind you it did start working for a day and then stopped again. The 8th digit of the vin is a 9
Expert:  Mike S. replied 1 year ago.

Are you saying that it goes to the full scale when the key is turned to start?

Can you gain access to the rear of the instrument cluster and check the voltage right at the gauge?

Expert:  Mike S. replied 1 year ago.

Wait just a minute on that. I see that both wires from that temperature sensor go to the ecm.

Customer: replied 1 year ago.
It does go to full scale when started and I do not have access to rear of gauge cluster
Expert:  Mike S. replied 1 year ago.

So, it must be the ecm that controls the function of the gauge.

Customer: replied 1 year ago.
Is that located at the drivers side wall of the engine compartment. Does the ECM provide the power to the gauge when the car is started?
Customer: replied 1 year ago.
To make it read full scale on start up
Expert:  Mike S. replied 1 year ago.

For now, here are the 2 wiring diagrams showing the wiring to the ecm at pins x3 35 and 55.

The sensor is at the bottom of page 3.

Expert:  Mike S. replied 1 year ago.

The only wires to the sensor go to he ecm, so yes.

Expert:  Mike S. replied 1 year ago.

Which wire by the way has the voltage, the yellow or pink?

Customer: replied 1 year ago.
I don't see the wiring diagram you sent me. Do you know if they can flash the ECM?
Expert:  Mike S. replied 1 year ago.

Yes, the ecm is under the hood on the drivers side.

Expert:  Mike S. replied 1 year ago.

Check the voltage again by backprobing the very same wire at the ecm.

Expert:  Mike S. replied 1 year ago.

I'll try the diagram again.

Expert:  Mike S. replied 1 year ago.

The ecm can most likely be flashed or reprogrammed but I would retrieve the codes first if the voltage is still the same at the ecm.

Expert:  Mike S. replied 1 year ago.

This is the explanation from the Mitchel manual and it assures somewhat what I already thought:

The instrument panel cluster (IPC) displays the engine coolant temperature as determined by the engine control module (ECM). The IPC receives a serial data message from the ECM indicating the engine coolant temperature. The engine coolant temperature gage defaults to 60°C (140°F) or below if:

  • The ECM detects a malfunction in the engine coolant temperature sensor circuit.
  • The IPC detects a loss of serial data communications with the ECM.
Expert:  Mike S. replied 1 year ago.

So, basically the ecm/computer should have a code stored. Let me know when you get the code.

Customer: replied 1 year ago.
My ECM only has 48 small pins and l large pin which does not match the wiring diagram
Expert:  Mike S. replied 1 year ago.

Are you sure then that you are looking at the ecm?

Customer: replied 1 year ago.
I pulled the ECM up online and it looks the same. It's about a 4 by 4 inch thin sealed aluminum with a 48 pin plug that mounts up on the drivers side wall by the fire wall
Expert:  Mike S. replied 1 year ago.

This should be what it looks like,

Expert:  Mike S. replied 1 year ago.

Chilton says it's on the lower air cleaner housing.

Expert:  Mike S. replied 1 year ago.

I believe you have to remove the air cleaner outlet duct. Here are the instructions on replacing it so it should show you how to gain access to it.

Expert:  Mike S. replied 1 year ago.

And to reprogram it you will need a tech 2 scan tool or equivalent and follow the instructions on the GM techline.

Customer: replied 1 year ago.
I found it under the air cleaner assy.. I have the same voltage on the yellow wire there. I don't need to clear the code to make it operate do I
Customer: replied 1 year ago.
can you tell me what pin goes out to the gauge and what type of voltage I should have on it.
Expert:  Mike S. replied 1 year ago.

No, clearing the code will do nothing as far as fixing it goes. As a matter of fact, you should not clear the codes until it is fixed.

Expert:  Mike S. replied 1 year ago.

I don't know which wire goes to the gauge or instrument cluster and anyhow I believe I did see that it was a computer data line and I don't think they can actually be tested for voltage per se. They should be checked with a scan tool. I would drive the vehicle to an auto-parts store and have the computer codes retrieved and ask about reprogramming the ecm while you are there.

Customer: replied 1 year ago.
I have a new snap on scanner it is out in the field. I will test it when he gets back and let you know.
Expert:  Mike S. replied 1 year ago.

ok

Expert:  Mike S. replied 1 year ago.

any news?