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.
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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.
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Re: A/C Compressor activation on P59

Postby ShorTuning » Mon Aug 17, 2020 5:44 pm

EDIT** Didn't see all these later replies but basically say the same thing.

The problem you are more than likely having is the analog input circuitry existing on the board of your PCM. All the swaps I've done with the P59 PCM that require analog AC functionality required a PCM hardware number that also had the IAC drivers. Spent about 2 days on a swap car figuring this out...

Customers car with supplied DBW PCM without IAC drivers would not see the analog AC input no matter what file I edited or flashed into the PCM. I had a shelf full of '243 PCM's with IAC drivers present so I pulled one to try. Flashed the identical file into that PCM and instantly the AC status input activated!

So for analog AC input to function pickup a P59 PCM with IAC drivers also.

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Re: A/C Compressor activation on P59

Postby rocketmench » Thu Feb 11, 2021 2:30 am

Hi all, I can confirm that certain P59 pcm's are missing the analog circuitry in the motherboard to process the 12V A/C analog request signal. The missing components in question are 2 resistors and a capacitor, all SMD. One resistor (3kohm) provides a pull-down function at pin C2-17. The other 100 kohm resistor and 1.5 nF capacitor act as a "debounce" or low pass filter to eliminate high frequency noise on the A/C request line. This information was determined by comparing to a PCM with those components.

The good news (at least to me), is that this can be relatively easily fixed by adding in the missing components. See my attachment for a description of how to do this.

In recent bench-top testing, I can confirm that adding in those components enabled the analog A/C request on two different PCM's that would otherwise only respond to the serial signal.

Another observation is that as part of the bench-top testing, I used an HVAC module wired directly to the pcm to test the serial A/C request. No BCM needed.

To "trick" the PCM into thinking it was running, I used a nano arduino and the speeduino ardustim code to generate the necessary crankshaft and camshaft signals. I configured the code to generate those signals directly without any external communication. I then used lsdroid and tuner pro to configure the A/C request configuration in the OS.

Incidentally, the XDF file I have does not include A/C pressure fan-on and fan-off parameters, just coolant temperatures. If anybody has and XDF that provides the full set of A/C fan configuration parameters for the 12587603 OS I would be greatful.

P59 PCM_iac_analog_AC.pdf
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Re: A/C Compressor activation on P59

Postby Gampy » Thu Feb 11, 2021 4:14 am

Are these what you're looking for in the 12587603 OS ??
Fan #1 A/C Pressure Enable
Fan #1 A/C Pressure Disable
Fan #2 A/C Pressure Enable
Fan #2 A/C Pressure Disable
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Re: A/C Compressor activation on P59

Postby rocketmench » Thu Feb 11, 2021 4:51 am

Well, when comparing to a screen shot from a posting online from somebody's EFILIVE session, I see I am missing:

G0903 "Fan #1 Turn-on by A/C Temp"
G0911 "Fan #1 A/C Pressure Enable"
G0912 "Fan #1 A/C Pressure Disable"
G0918 "Fan #2 A/C Pressure Enable"
G0919 "Fan #2 A/C Pressure Disable"

tunerpro_acfan_parameters.jpg
tunerpro_acfan_parameters.jpg (76.13 KiB) Viewed 104 times

efilive_acfan_parameters.jpg
efilive_acfan_parameters.jpg (206.87 KiB) Viewed 104 times

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