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My son's 97 Eldorado is running warm when sitting in traffic. The cooling fans are not kicking on even at 240°, should kick on at 225°. We checked the 50 amp maxi fuse and it was fine. We unplugged the wires to one fan and there is no power even at 240° coolant temp.

Edited by caddidaddy55
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It's probably one of the relays or connectors. Could you run the OBD codes and post them here? That will likely help; I'll get out the schematics from the FSM and get back with you tomorrow.

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-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Check your codes here

http://myweb.accessus.net/~090/dtcobd2.html

I don't see anything in your codes that would cause a problem with your cooling fans, but I would look at the Network code U1255 closely.

You should have 2-30 AMP fuses, cooling fan 1 and cooling fan 2, check those fuses

The PCM grounds the fan relays to engage the fans, you need to check the connections C1 and C2 at the PCM

I would check the fan motors also, along with the connectors.

if you do a search, I have posted lots of schematics on the cooling fan circuits

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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P0603 Control Module Long Term Memory Reset

U1255 Class 2 Communication Malfunction (Serial Data Line Malfunction)

B1319 Sunload Sensor Short Circuit

B1348 Very Low A/C Refrigerant Pressure

B2477 Reverse Lamp Relay Shorted to Ground

B2120 Lumbar Up/Down Sensor Failed

Only B1319 has anything at all to do with the A/C or cooling and that won't keep the fans from coming on. We can go through these when we are done with the fans if you like.

One of BodybyFisher's posts with the fan schematic is here:

In the 1997 FSM the schematic has been moved to the Engine Cooling section and put on one pate, 6-176, but the wiring diagram is the same except for the connector terminal designation to the compressor clutch, which is of no interest to us. The keys here are that the relay coils get their power through the 10 Amp fuse labeled AC COMP (ORN wires to the relays), but the power that is switched by the relays and that runs the fans comes through the 50 Amp fuse labeled COOL FANS. Both are in the groups of fuses and relays under a plastic cover behind the air cleaner housing.

Relay no. 1 has 4 wires, RED, ORN, DK GRN, and BLK.

Relay no. 2 has 5 wires, BLU, ORN, WHT, BLK, and DK BLU.

Relay no. 3 has 4 wires, RED, ORN, DK BLU, and LT BLU.

When the fans are on low speed, relay no. 1 is ON while relays no. 2 and 3 are OFF. The fans are in series, with 6 Volts across each.

When the fans are on high speed, relays no. 1 2 and 3 are all ON, and there is 12 Volts across each fan.

The RED wires are the ones with power from the 50 Amp COOL FANS fuse. The ORN wires are the ones with power from the 10 Amp AC COMP fuse.

Avoid touching the DK GRN and DK BLU wires. They go to the PCM. The FSM warns that the PCM, which is a computer (or module), and is static-sensitive. The FSM has a general warning not to back-probe (use a meter to check voltage or resistance through the wiring harness) wires that connect directly to any of the modules. The PCM operates the relays by grounding these wires.

With the fans never coming on at all, you problem is most likely one of the fuses, relay 1, one of the fans, or a bad connection in the wiring harness, with likelihood approximately in that order.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks Jim.

That schematic Jim referred you to shows one 50 amp fuse. When I checked the 2000 factory service manual, it shows 2 - 30 amp fuses.

You said you checked the 50 am fuse, what year do you have? Is this a 2000?

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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Oh, I just looked back you are working on the 97 not the 2000, sorry..... you do have a 50 amp fuse, those schematics are OK for your purpose

Its a pretty logical circuit and you can follow the flow through the relays to diagnose it

As Jim noted, Relays 2 and 3 are fed by Relay 1, I'd swap in a known good relay from a scrap yard to quickly eliminate the possibility that the relay is toast

By the way, see if you can list both the 97 and 2000 under your profile so it shows under your name

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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They are straight down below the cooling fans, there are three grouped together, they are behind the radiator at the bottom

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I believe that numbers 1, 2 and 3 are from left to right in sequence but you can identify them by the number of wires (four for no. 1 and no. 3, five for no. 2) and wire colors; relay no. 1 is the one with a BLK wire but only four wires.

For starters, I would check for voltage on the ORN and RED wires on any one relay. Lack of voltage at either of these points would cause your problem and immediately lead back to a fuse, connector, or the wiring. The only solid ground is the BLK wire on relay 2 and the RH cooling fan.

Given voltage on the RED and ORN wires, you can turn the key on with the A/C on (you don't have to start the engine and can do this with the car cold), then see if you have 12 Volts on the BLK wire on relay 1. If you do, then the fans are being turned on. If not, try switching relay 1 with a known good relay of the same part number.

You can do a quick check right then on the fans. Check the voltage across them. If the voltage is at least 6 Volts across a fan and it isn't turning, it's bad.

If you get 12 Volts on the BLK wire on relay 1, relay 1 is good, or at least the normally open contact that is used there. If you get 0 Volts then relay 1 is bad.

Then check the WHT wire on the LH cooling fan or relay 2. The "correct" reading on the WHT wire is about 6 volts, and it will be a shaky reading, with both fans running at low speed. Whatever it is, you should get the same reading on the LT BLU wire on relay 2, the LT BLU wire on relay 3, and the LT BLU wire on the RH cooling fan. If you get different readings on the WHT and LT BLU wires when the A/C is on with a cold engine, then relay 2 is bad, or at least the normally closed contact used there is bad on relay 2. If it's 6 Volts are less and the LH cooling fan isn't running the LH cooling fan is bad. If you get at least 6 Volts and the RH cooling fan isn't running, then the RH cooling fan is bad.

After you get that far report back and we'll go from there.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Hi all, just checking back in. My son has had to work late all week, but he has Fridays off. It turned out to just be a bad connection at the relays. All is working well now, fans come on at 228° back off at 212°. Thanks again for your help.

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Excellent. Thanks for getting back and letting us know how it worked out.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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