Engine fan running 1/2 speed and relay clicking

[jrpontiac]

I am working of the relay setup for my engine fans on my LS conversion. I got a dual fan setup with each fan triggered by a relay that is activated by the engine PCM. Each fan has it's own relay. The PCM activates the fan relay by triggering the ground. My problem is that when the pcm triggers the fan (about 190degrees) that fan only runs 1/2 speed, maybe less. The relay is also clicking, both relays click. When I bypass the PCM ground with a wire clipped to a solid ground the fans click on 100% and the relays don't click.

So I assuming I have a grounding issue, my problem is I don't know how to improve the ground since it terminates somewhere in the PCM.

Any suggestions?

[Dead Parrot]

If I read this correctly, the relay coils are switched by the PCM on the ground side. Where are the fans themselves grounded? If the fans are trying to get a ground via the PCM, could be overloading the PCM ground wire. Not a PCM expert but would think the fans would ground independent of the PCM.

[jrpontiac]

The fan have their own ground, which I believe is adequate because when I activate the relay by grounding it to the neg battery post the fans work great. When I let the relay be activated by the pcm ground switch the fans don't work so great.

[StorminNorman]

What PCM is this ? was it a truck PCM ? Did you have it programmed correctly for electtic fans ?