Low82C10

i have a 82 c10 pickup with a 2004 tahoe 5.3/4l60e
i got it running it drives etc, the problem is i have a relay for fan1 and relay for fan2 from the guy who did my harness so all i needed to do was run one wire from each relay to my fan. well when i 1st start the truck, fan1 relay will click on and off about every 5-10 seconds, before it even needs to kick on. well yesterday i finally let it warm up to kick the fan on which i think is like 240something? and fan1 kicked on and was running like it was suppose to, but then fan2 tried to kick on but the relay was just clicking every second click,click,click,click,click and the fan was on/off/on/off/on/off.

what's going on here? i cant keep taking an hour drive to the dude who did my harness to check my computer he said maybe he didnt select two fans, now he wants to change fan2 turn on temp? i know he used HPtuners but i think i have read that since 2004 tahoe didnt have two fans its been a problem...any help?

kossuth

iTrader: (12)

Well, first off sounds like you have a wiring or a relay issue preventing the second fan from coming on. Quite frankly if you are using a factory LS1 PCM I would go about this differently. I would setup a three relay circuit and create a low speed high speed setup for both your fans so they both run at a certain speed. Unless you have something unique going on with your cooling setup low speed and high speed setup is honestly the way to go. Either way you have a wiring issue. Either a crappy ground, or a loose connection or something. Unless the PCM is damaged it would just toggle fan ground on and run it till the vehicle was below a set temp. Not on/off on/off on/off real quick like.

Also, just noted you said the donor vehicle was a Tahoe. I believe the only fan circuit for those was to blow air through the AC condensor and wouldn't really come on unless commanded by the PCM for AC functions. Unless I'm mistaken the actually vehicle cooling was done via clutch fan. Now, the truck and fbody/vette PCMs are the same and the pinouts are the same so if push comes to shove you could just flash it as a fbody, but you shouldn't have to do that if he knows what he's doing with the software.

Low82C10

what would that three relay setup all involve? is it something that would need to get programmed into the pcm etc?

Low82C10

thats what i was thinking that it could be a bad ground but i wire brushed them and re checked my grounds. its just weird that before it gets to temp to kick the 1st fan on,fan1 is already trying to kick on and kicks right back off.

green96ta

iTrader: (11)

Thats an odd issue to have. Obviously the pcm has been tuned for fans or they wouldnt even try to kick on.

First, the easiest thing to do is swap relays and see if the problem follows the second fan relay.

You should be able to use a meter and check for power between terminals 85 and 86 on the relay connector, the easiest way to do this is jump out the coolant temp sensor pigtail with a piece of wire and the pcm will automatically kick the both fans on. Just dont short the wire to a power source. All the pcm reads there is resistance across the sensor.

If you are losing the circuit at the relay connector I would make sure to check the power side, and then check the ground circuit to the pcm.

The pcm supplied the GROUND to the relay coil. I hope this helps.

who re-done your harness?

Low82C10

I switched the relays and the problem still continues, i checked both relays with a 12v source and between the other two pins and they did check out fine. by jumping out the temp sensor you mean get a wire and put it to both wires on that pig tail right? and can you explain the power side of the relay a little please? like check to make sure i got consistent power to the relays? how do you check to make sure i got a good ground. i wire brushed the fram really good where i have my ground to, i have three grounds one from the cab to the frame and that same spot on the frame i have my engine ground, and i have a engine block to frame on another sppot.

green96ta

iTrader: (11)

Yes, put a jumper wire between the two wires.

It just depends on how the relay connector was wired, power could be 85 or 86. it does not matter how its wired and which one is power strictly depends on who wired it. take one of your meter leads to a good ground with the ignition on and test to see which one is the power. If your meter gives a steady reading then its most likely the ground giving issue. The ground is provided by the pcm, and a inconsistent engine harness ground could cause this issue. That should get you started.

robbied31

iTrader: (1)

I had the same problem with an LQ4 from a 2000 truck. There was only one fan on the truck and I went to dual fans. All the pinouts showed a fan2 circuit but it did the same thing you described. Turns out that circuit is for a recirc vent (used with the AC) and functions differently than a fan circuit. That's why it starts and stops. This was brought to my attention at the HP Tuners website. i sent them my tune and they "hacked" my tune file for the fan2 circuit. At the time you couldn't change the circuit within the current software. Don't know if there is a new version now or not.

If your tuner uses HP Tuners, have him contact support. Not sure about the competitor.

Rob