mikezohsix

I have a 2004 GTO motor and PCM.
In this car the low speed fan is controled by the body module. There's no wire listed on the PCM pinout for low spd, though there is one for the high spd.

I was wondering if other cars had the low spd fan controled by the PCM and if that pin might be active on my PCM, but just not listed because it isn't used on th gto?

69 Ghost

Tunercat added control for the PCM to control the A/C switch instead of the BCM which should in turn make the fan control come from the PCM but it has not been tested -yet. I am going that direction over the 411 but also have a 411 as a backup in case it does not work. This would require programming to your PCM.

mikezohsix

so you're saying in the original car, the low spd fan was turned on by the AC, and the high speed was temperature related - did I get that right?

Then there is no low spd fan signal on any LS PCM?

arthropraxis

The F-body PCM has lo and high speed fans in addition to A/C request on the PCM. I am using a GTO motor and switched to a F-body PCM to get those features without getting it reprogrammed.

Andy1

Is the AC request a +12V signal to the Fbody PCM?

Thanks,

Andy1

arthropraxis

From what I understand the F-body is a 12v signal, that is why I am using it. The GTO PCM that came with the motor doesn't have A/C request, it is handled by a class2 serial data line from the BCM.

69 Ghost

The statements are correct in the stock GTO tune runs the first fan and A/C off the BCM but keep in mind if you have a 2004 GTO motor and harness and if you decide to go to a 411 PCM you will still need programming. Either way there is really no way around it. As stated the latest Tunercat definition has the switches to change the A/C request to the PCM and it also has a fuel segment switch so you can run your fuel gauge off the PCM for more accurate results. Also the grounding in the 04 O2 sensors are different than the 02 O2 sensors and you will need to deal with that.

69 Ghost

The alternator wiring is also different and will have to be dealt with.

arthropraxis

The alternator should be easy enough as it does not have to be connected to the PCM. What can be done for the O2 sensor grounds?

arthropraxis

69 Ghost, I have both PCM's, the F-body ,programmed with a mail order tune, and the GTO. I found the F-body grounds for the O2 sensors are at the body and the heater is through the relay. The GTO is grounded through the PCM. Can the F-body be programmed to ground the O2 sensors through the PCM?

arthropraxis

Pin 42 on the blue connector can be programmed to turn on the low speed fan relay for the GTO PCM. If the A/C request signal can be confirmed to be activated by the GTO PCM then the fans should work as they are supposed to. Right?
If so, does anyone have access to the software and want to program my GTO PCM?

busta9876

iTrader: (3)

I used a 2004 GTO base calibration in my 86 k5 blazer with a 5.3L and TH400. (cable throttle) I made no special changes and my low speed and high speed works fine off blue pin 42 and red pin 33. I just set the temps and it worked.

As for the o2 sensors, GTO uses what are called isolated ground sensors. 2003+ PCM's ground the TAN wires going to all 4 o2 sensors internally. In the 2002 and down PCM,s the tan wires had to be grounded external from there. So for 2002 and down you had two options. CASE Grounded o2 sensors, where the sensor had to be grounded in the exhaust pipe, or some 2002 down also had ISOLATED ground sensor, however, since the tan wires were not grounded by the PCM, harnesses setup for ISOLATED ground sensors had a large splice pack with all the tan wires from all 4 sensors, 4 wires going to the PCM tan wire locations, and 1 more wire going to a LOW REFERENCE pin on the PCM. (4 wires to o2's, 5 wires to PCM) see here for more info. http://www.lt1swap.com/vortec_o2_sensors.htm

All the LS1's used case grounded sensors, 99-02 could use either, or sometimes both types in the same harness. (6.0L, 8.1L)

-Brendan.

69 Ghost

That is good to know I did not test this. For the O2 sensors it is a little more complicated than that. The 04 GTO has some additional diagnostic capabilities than the 02F-body 411's. One of the reasons for grounding the O2's to to the PCM.

arthropraxis

Well, that answers the low speed fan question. If it can be confirmed the A/C request can be programmed then I can use the GTO computer.

busta9876

iTrader: (3)

You can always use that computer with a base express van calibration. The express vans use an a/c system with a/c request going through low side cycle switch first, then on to the PCM. PCM from there controls the a/c clutch relay.

There are several types of a/c systems. Some tuning software I use will let you choose the a/c system type.

arthropraxis

Brendan, thanks for the info. That may work for what I need. I am doing a conversion on a Porsche 944 with a 2004 GTO LS1. If the GTO PCM is enabled to control the clutch relay will it turn on the second fan with it?