A/C Compressor activation on P59

They go by many names, P01, P59, VPW, '0411 etc . Circa 1999 to 2006. All VPW OBD2 PCMs.
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Re: A/C Compressor activation on P59

Postby PeterTremonti » Thu Jul 30, 2020 5:09 am

20200729_125034.jpg
It looks like the compressor from a 2003 express van has an extra connector in the back. Not sure what it's for yet but there is a difference between what I have and what the PCM would be expecting I think if I tell it it's a van.

Does anyone have a picture of the inside of a P59 from an express van that would show the traces? I opened mine and it doesn't look like they go anywhere electrically on the surface. Maybe there's an internal layer to the PCB? Not sure.

Gmpartsdirect.com shows PCM for a 2003 Express to be 12581565 and the suburban to be 12581565 or 89017750 (which replaces 12602802). I don't have any more info on the part numbers and am mostly curious what the insides of a van PCM look like to compare with my PCM.

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Re: A/C Compressor activation on P59

Postby ironduke » Thu Jul 30, 2020 5:45 am

Multilayer circuit boards make it pretty difficult to follow traces.. I'm wondering if you write the analog switching cal to it and then put voltage to pin 17 if the data list for ac request changes to yes.. don't know if it needs to be running? Could also provide voltage thru the low pressure cycling switch(pin 55) and see if it grounds pin 43.. Should see data list show a/c request and ac clutch commanded change.. if it does all that then your done and you'll be ready for when your lines are done..

Below is Silverado compressor controls, they are different.. Trucks use a a/c pressure sensor in the high side line instead of the high pressure cutout switch.. Not sure what else is different yet

2004.Silverado.Compressor controls.pdf
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Re: A/C Compressor activation on P59

Postby Gampy » Thu Jul 30, 2020 8:01 am

I have a 2003 Express unit setting here ... HW:12575502 SVN:12581565 - 2003 Chevrolet Express Cargo Van 2500 AWD - Automatic M30 4L60E - 5.3L LM7

I believe non IAC units do not have the hardware to do analog A/C.

You might like to have a look at a 2004 Vette, I believe they are DBW, Analog A/C on a IAC unit. I could be wrong.
I'm not angry, I'm a brash, blatant, driven, passionate individual that is extremely intense!

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Re: A/C Compressor activation on P59

Postby PeterTremonti » Fri Jul 31, 2020 2:09 am

Gampy wrote:I have a 2003 Express unit setting here ... HW:12575502 SVN:12581565 - 2003 Chevrolet Express Cargo Van 2500 AWD - Automatic M30 4L60E - 5.3L LM7

I believe non IAC units do not have the hardware to do analog A/C.

You might like to have a look at a 2004 Vette, I believe they are DBW, Analog A/C on a IAC unit. I could be wrong.


I found something yesterday on LS1Tech.com that said something similar about needing to have a PCM with IAC hardware to make the A/C work with a 12V signal on pin 17... I'll have to check the other PCMs I have laying around here and see if any of them have the parts to make this work before I buy another PCM.

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Re: A/C Compressor activation on P59

Postby PeterTremonti » Fri Jul 31, 2020 6:21 am

Assuming the DBC PCMs are the only possibilities, I've found a list from LT1swap.com. To quote their page http://lt1swap.com/cable_conversion.htm


What makes things nice, is GM still used a Cable throttle body in the Express Vans with the 4.8/5.3/6.0L engines until 2005 and the GTO in 2004. To allow cable throttle, the PCM has to be able to control the IDLE AIR CONTROL (IAC) motor. This is simply a stepper motor. As the stepper motor turns one way or another, it opens or closes a valve, and controls air flow into the engine. I have identified the PCM's 2003-2007 that WILL SUPPORT the idle stepper motor required for Cable Throttle Control. (MOST PICKUP TRUCK PCM's DO NOT SUPPORT DBC) If your number is 1 digit off, it won't work.

1999-2002 Serv. No. 09354896, 12200411 - All BLUE/RED connector PCM will work with either drive by wire, or drive by cable, the PCM simply needs programmed correctly.

2003: Serv. No. 12576106 with Hwd. No. 12570558 - Most all 2003 trucks should have this PCM

2004: Serv. No. 12586243 with Hwd. No. 12583659 - Mostly GTO and Express vans got this PCM, as well as Caddy CTS-V. MIGHT be in trucks.

2005-2006: Serv. No. 12589462 with Hwd. No. 12589161 - I think you'll only find this in Express Vans. Maybe in some pickups.

2007: Serv. No. 12602801 with Hwd. No. 12589161 - Found only in Express Vans (even if the VAN was DBW, it supports cable throttle)

Also, a tip on finding these. Any 4.3L V6 Pickup or S10-S10 Blazer/Jimmy will have the above computer, and can be programmed for the V8 Gen 3 LS engine.


05:01pm - Found another list from https://www.mrk-motorsports.com/gm-iac-pcms/

GM PCM’s with IAC drivers (needed for “Drive by Cable”)

SERV. NO.- HWD NO. –

12200411 – xxxxxxxx – 2002 F-Body, Corvette, S10, IAC DRIVERS INSTALLED
09354896 – xxxxxxxx – IAC DRIVERS INSTALLED.
12576106 – 12570558 – 2003 G-VAN, LM7, IAC DRIVERS INSTALLED. ALSO C-TRUCK LM7

12582605 – 12580786 – 2003 C-MPV, L59
12586242 – 12583660 – 2004 C/K-TRUCK, LM7

12586243 – 12583659 – 2004 GTO LS1, IAC DRIVERS INSTALLED
12589463 – 12589162 – 2005 C/K-TRUCK/MPV, LM7, LQ4
12589462 – 12589161 – 2005 G-VAN, LQ4, IAC DRIVERS INSTALLED
12589463 – 12589162 – 2006 C-PICKUP, LM7
12602802 – 12589162 – 2006 C-PICKUP, L59

12602801 – 12589161 – 2006 – 2007 Express, Drive by Wire, IAC DRIVERS INSTALLED

Green = IAC Driver Circuit Present

Red = IAC Driver Circuit NOT SUPPORTED
Last edited by PeterTremonti on Fri Jul 31, 2020 7:04 am, edited 1 time in total.

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Re: A/C Compressor activation on P59

Postby Gampy » Fri Jul 31, 2020 6:47 am

Those lists are missing HW:12575502, SvN:12581565 ... Other then that they match the hardware list I posted.
The first one on the first list is a P01, the first two on the second list are P01's, all P01's have IAC.
I'm not angry, I'm a brash, blatant, driven, passionate individual that is extremely intense!

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