My son's 2004 Bonneville GXP destroys the Coolfan S/P Relay #39 and a has melted the fuse contacts for that relay on the fuse board. The fans have been removed and tested off the car. They seem to work fine. Wires and connectors for the fan motors seem OK. Does anyone know what could be causing this? Thanks.

There are three components of any electrical circuit.

1) Source
2) Path
3) Consumer

In this case you know #1 (the power source delivers power), works. You now know #3 (the consumer or the fan(s) ), work. So process of elimination is...

Sounds like a harness with a short somewhere and/or a bad ground, and/or bad connections.

_________________


Retired Bonneville Owner and former GM Tech:
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I agree with above.

As soon as there is any bit of looseness in that relay connection it will begin to overheat due to that weak connection not being able to carry the current draw needed to run the fans. You will likely need to replace the contacts that are melted then test the wires to make sure they are good.

_________________
Ryan

2003 Bonneville SSEi - The Black Mirror SOLD!
2002 Bonneville SE - The Mutt Complete 2004 SLE interior, drivetrain, and body harness swap, ECC swap, HUD swap, black GXP wheels, GXP headlights and tinted tails - SOLD
2003 BMW 540i M Sport, 2001 BMW X5 4.4i, 2010 GMC Acadia, 2017 Grand Design Imagine 3150BH
1982 Cutlass Supreme - The fun one

Relay 39 controls the left cooling fan. However it is a little more complicated than that. The realy is a single pole, double throw relay. Meaning, when it is energized by the PCM, current flows through the relay switch from the low voltage end of the right cooling fan to ground for the high speed right fan control. It is a white wire running from the right fan to the fuse block into relay 39. The other end of this circuit goes to ground. When the relay is not energized it sends the current from the white wire from the right cooling fan through a light blue wire to the power side of the left cooling fan so they are hooked up in series and run at lower speed, The other wire from the left cooling fan is going to ground. When relay 37 is energized it sends 12 volts directly to the left cooling fan through the same light blue wire for left fan high speed. All of this is controlled by the PCM.

With the key in off position, and relay 39 removed, check the white wire from the right cooling fan to make sure it is not shorted to ground. Do the same for the light blue wire from the left fan. Also check the dark blue wire from the relay to the PCM to make sure it is not shorted to ground. If this wire is shorted, remove relay 37 and test it again. If the short goes away, relay 37 may be bad or the wire from relay 37 that connects to the PCM (splices into the dark blue wire from relay 39) may be shorted. You may have to snap the fuse block out it's case and look underneath to locate this wire and test it. If any of these wires is shorted, then you will need to locate the short and repair it. It is also useful to know which connectors burned out on the relay. This relay has 5 contacts. The top right contact is the white wire running to the right fan. The center bottom contact runs to the left fan light blue wire. The bottom right runs to the PCM dark blue. The bottom left runs to ground, black. The top left runs to fuse 46,

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bobgto65

2004 Bonneville GXP 62,000 miles purchased 04/13
2009 G8 GXP PBM, M6 9580 miles, no mods, sold 08/15
2009 G8 GT SBM 36,000 miles, modded 430 whp
2002 Bonneville SSEi 203,200 miles (sold 3/2014)