electric fan circuit expert wanted
Thread Starter
3rd Gear
Joined: Mar 2008
Posts: 3
Likes: 0
From: Whitehouse TX
electric fan circuit expert wanted
Hi all, I am looking for help with the coolant fan circuit on my 98 C5... My PCM will not turn on the fans due to coolant temp. The fans turn on and function correctly based on A/C head pressure (both high and low speeds). All three coolant fan relays and all fuses are good.
The PCM will not ground relay 45 when the temp comes up. As soon as you turn on the A/C, relay 45 gets its ground and the fans turn on.
The Coolant Temp Sensor is reading correctly and the gauge in the instrument cluster is reading correctly. Is there any way the CTS would communicate with the instrument cluster and not the PCM? Does the instrument cluster get the temp from the PCM or straight from the CTS?
I have the factory service manual for the car, but I cant find the instrument cluster temp gauge circuit.
Thanks for the help!
-Ryan
The PCM will not ground relay 45 when the temp comes up. As soon as you turn on the A/C, relay 45 gets its ground and the fans turn on.
The Coolant Temp Sensor is reading correctly and the gauge in the instrument cluster is reading correctly. Is there any way the CTS would communicate with the instrument cluster and not the PCM? Does the instrument cluster get the temp from the PCM or straight from the CTS?
I have the factory service manual for the car, but I cant find the instrument cluster temp gauge circuit.
Thanks for the help!
-Ryan
Thread Starter
3rd Gear
Joined: Mar 2008
Posts: 3
Likes: 0
From: Whitehouse TX
I was not aware that the fans are prgramable....My factory service manual says that the fans are programmed to turn on low at 219F. Seems a little high to me, but thats where they set it.
How do you program the fans? Do you have to have an OBDII scanner??? I will see what I can find searching.
How do you program the fans? Do you have to have an OBDII scanner??? I will see what I can find searching.
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
I was not aware that the fans are prgramable....My factory service manual says that the fans are programmed to turn on low at 219F. Seems a little high to me, but thats where they set it.
How do you program the fans? Do you have to have an OBDII scanner??? I will see what I can find searching.
How do you program the fans? Do you have to have an OBDII scanner??? I will see what I can find searching.
In your Service Manual, if you want to see where the IPC gets the colant data (from the PCM via the Class2 serial data line) , turn to the section called Instrument Panel, Gauges and Console and look at the wiring diagrams in the start of the section. You are looking for Instrument Cluster Schematics (Temperature, Fuel, and Oil Pressure Gauges.
If you want to see how the PCM gets the coolant data, turn to the Section called Engine Controls - 5.7L and look for the schematic labeled Engine Controls Scematics (Manifold Absolute Pressure (MAP) Engine Coolant Temperature (ECT) Vehicle Speed and Engine Speed Output.)
Notice that most engine sensors are wired direct to the PCM, and it then "ditributes" the data to other computers using the Class2 serial data line.
