PCM Wiring Fan Relay Control

I plan on keeping the 944 fans and will have the stock sensor (stock radiator set up). This is controlled by the existing porsche wiring and relay, correct?

There is no reason to keep PIN 42 (low speed fan relay) on the BLUE Plug or PIN 33 (High Speed fan relay) on the RED plug, right?

Good question, I was planning on the same. I think you can as long as the computer is reprogrammed to take them out. Anybody?

I only saw DTC codes for the fan relay control circuits, not sure if the code would be reported if the fan relays are not hooked up, and the ECM not to report on the error code. I opted for using the GM computer to control the fans, since I can program the on and off temps they activate at with HPTuners.

You guy's are KILLING ME!


Stop trying to use all that wore out Porsche wiring and relays, The relays in your Porsche is on of the things that will leave you on the side of the road in a heart beat.
Wire your fans with new wires and new relays, hook them to the ECU and let the computer turn them on when it needs them, not the Porsche sensors. They may have a different temp setting than your motor needs after programing/ tune.
That goes for the DME relay to. DO NOT USE IT! Rewire it with a standard relay that you can get at any part store. $5.00 compared to $35.00 sounds a heck of a lot better to me. The Porsche DME relay is notorious for going bad.

That just makes way too much sense.

THANK YOU!

Exactly what I did for the same reasons, minimized the Porsche wiring for the LS1, ran a boatload of new wiring. The fan relays were simple to wire up, they work perfectly. My radiator doesn't have the Porsche bung for the temp switch, I had it made that way. I totally agree on eliminating the DME relay, it's a known 944 weakness. Fresh realys are cheap, easy to wire, and the wire available today has much better coatings resistant to heat, chemicals, etc. Rewire that old stuff!

What temp switch did you use? Where did you put it?

ECU............................It controls the fan relays.
No temp switch needed. The ecu uses the temp sensor on the drivers side head to read engine temp and then the ECU controls the fans as needed. 2000 technology .........It's great ant' it
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Sorry, but I am going to have to tread jack for a minute here. I was going to use the Porsche wiring for the A/C compressor and fans. When that setup is used the second fan kicks on automatically when the A/C is turned on. When the LS computer controls the fans and the Porsche wiring controls the compressor that would no longer happen. Could I keep the A/C wired through the Porsche harness and the LS computer kick in the fans just as a result in the rise in temperature or is it necessary to wire the compressor to the LS ecu?

Great Question!

I think it is better to wire the A/C compressor to the LS computer, and supply 12V to the A/C request input when the A/C is switched on. That way the LS computer can alter the engine idle, etc for the load of the A/C. It will also switch the fans into high speed when needed. With the LS setup, at low speed, the fans are in series, when high speed is kicked in, each fan gets 12 volts independently. If you wire the fans into the LS computer, it will also turn them off at 35 MPH or so when they are no longer needed, provided you have VSS hooked up. It's only a few wires to add the A/C control to the LS computer. Just my thoughts on the subject.

Do I have to braze in the pressure switch in the A/C high line with that setup? I need more of your thoughts, I am pretty much thoughtless on the whole wiring aspect. I contacted you before about this then someone else suggested to use the Porsche harness for the A/C. Now I have come full circle and I am back to using the LS1 PCM.

Yes you have to put in the GM pressure sensor, I forgot to mention that, it's not a big deal, ports are available from a variety of sources. PM me for contacts, I'm happy to help.

I thought so, that is one of the reasons for wiring it with the Porsche harness. I found that docsblocks.com had the fitting for the sensor. When I start the wiring I really will have a lot of questions.

This would be excellent to have all documented, the wiring for fans, A/C, relays, sensors. This does sound like a better way to go go. From the manual, I thought the what to do this was with the porsche stuff.

This would be awsome to set up and it sounds like it would be easy if it were detailed. Would be a great update to teh manual for sure.