Blue67LS2

iTrader: (2)

Both of my fans kick on approximately 10 seconds after my engine starts (hot or cold). I'm running a LS2 with a custom harness that has separate relays for each fan. I have a Vintage Air system, but it is not currently installed.

Seems like I recall reading somewhere on here that an "open" circuit on the AC either sends or causes the computer to detect a high pressure condition / reading (whatever that is) which causes both fans to run at max output? I've search like mad, but I can't find anything on this? Is this true and how to I trick the computer in the meanwhile?

I would appreciate any input from the LS gurus out there... Thanks!

buddyholly

Here is a link to a discussion on the issue. Hope it helps...
https://ls1tech.com/forums/pcm-diagn...ans-issue.html

FastKat

iTrader: (10)

I am pretty sure the fans have two speeds: low and high. In low, both fans turn at a lower speed because the relays wire them in series, giving them each half the electrical system's power. In high, the relays wire the fans in parallel, giving each one the electrical system's full power.

This may help explain why both fans run at the same time, rather than just one running at a time.

Blue67LS2

iTrader: (2)

Thanks for replies. I don't understand why the fans would come on when the engine is cold. Not sure about the two speeds, but I can't imagine mine going faster than they are currently. It seems as if the PCM is sending Max power.

Clyde65

how are the fans controlled? via the PCM or via a relay/programable unit? or are they just wired in through the relay? might explain it.

Blue67LS2

iTrader: (2)

The fans are controlled by the PCM. The settings appear to be correct based upon the scanner we checked the system with. Oddly enough we could toggle the fans with the handheld (scanner) as long as the engine wasn't running. Upon start however; we could no longer overide or manually turn them on or off with the scanner. Still scratching my head on this one...

FastKat

iTrader: (10)

I know it's a long shot, but is your engine temp sensor reading correctly (through the PCM, not the gauge)? An artificially high (or faulty) temperature reading would probably turn the fans on high after you start the engine.

Blue67LS2

iTrader: (2)

Updated with a new problem...

I determined the fans were running constantly because ECM was programmed to accomodate the factory AC system. My programmer removed these codes / setting and wa la... the fans no longer come on at start up.

The new problem is that they refuse to come on at any temperature now! That old saying about taking one step forward and two steps backwards is proving true... ugh!

Any thoughts or ideas as to why the fans won't turn on now?

BelAir1000

iTrader: (1)

Are you still able to toggle the fans with the engine off?

99_LS1_WS6

iTrader: (5)

There could be a couple of things to check out, the engine temp sensor could be going bad. The other is that it could be in the tune in the PCM.

BelAir1000

iTrader: (1)

If your still able to turn the fans on and off with the engine off, I think its still in the software.

If the fans cannot be commanded on/off with the engine off, I would confirm where your relays are getting their power. What is your relay setup?

psiconversion

iTrader: (5)

Are you still running an LS2 PCM? Is this a 58x or 24x application?

Blue67LS2

iTrader: (2)

I'm running a 2005 E40 ECM/PCM that has been bench programmed for my specific application (vats removed, 2 O2 sensors, etc.)

My engine is an early model 24x reluctor LS2 engine. Appreciate any additional thoughts?

BTW - I don't have Tech 2 and my car is the build stage which makes it difficult to get to a shop, so I don't know if the fans can be toggled manually. I was hoping to avoid this step, but it may be inevitable.