For those of you who are running P59 ECU with OS 12587603 along with a manual transfer case or you just simply want the 4WD indicator light to come on on your dash when 4WD is engaged this is how you fix it. to start i have looked at many, many variants of 7603 OS in hex comparison software and not a single one has the 4WD indicator output enabled in it. Doing this is literally the same as the voltage gauge fix where 5 bits needed changed to enable the output from the ECU for the cluster over class 2.
This is for 12587603 OS only. it might work on others but i dont know. I put together a quick dirty tuner pro patch with the maps that get changed in it. mouse over the read me!! in the XDF menu, apply the patch, see the difference it made and than smile because your 4WD indicator works now. also make sure you have the P01/P59 checksum plugin installed, the XDF will automatically correct the checksum when you save it. if you dont have it installed tuner pro will bitch about it lol.
Forgot to mention i threw a patch in there for the voltage gauge fix for those of you running 03-06 IPC's in your 99-02 trucks or SUV's too.
4WD IPC indicator fix with 12587603 OS
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dubcrazy8392
- Posts: 38
- Joined: Fri Jul 18, 2025 10:57 pm
- cars: -1981 6.0L LQ4 swapped C10 (aka lumpy)
-2000 silverado 2500 (daily work horse that does it with style)
4WD IPC indicator fix with 12587603 OS
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Last edited by dubcrazy8392 on Wed Dec 10, 2025 4:40 am, edited 1 time in total.
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sparepartsblazer
- Posts: 101
- Joined: Mon Dec 04, 2023 1:18 am
- Location: Missouri
Re: 4WD IPC indicator fix with 12587603 OS
Will have to try this out.
Now if we can just kill that damn pesky ABS Light.
Now if we can just kill that damn pesky ABS Light.
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dubcrazy8392
- Posts: 38
- Joined: Fri Jul 18, 2025 10:57 pm
- cars: -1981 6.0L LQ4 swapped C10 (aka lumpy)
-2000 silverado 2500 (daily work horse that does it with style)
Re: 4WD IPC indicator fix with 12587603 OS
Actually i outlined how to do it with an 03 IPC running 15104999 calibration which can be found in the IPChammer program in this post. im sure with a hex comparison tool you can find the same bit pair in other year OS calibrations and turn off the ABS light too.sparepartsblazer wrote: Tue Dec 09, 2025 12:59 pm Will have to try this out.
Now if we can just kill that damn pesky ABS Light.
viewtopic.php?t=9091
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sparepartsblazer
- Posts: 101
- Joined: Mon Dec 04, 2023 1:18 am
- Location: Missouri
Re: 4WD IPC indicator fix with 12587603 OS
Im using an 07 Envoy IPC in mine.Actually i outlined how to do it with an 03 IPC running 15104999 calibration which can be found in the IPChammer program in this post. im sure with a hex comparison tool you can find the same bit pair in other year OS calibrations and turn off the ABS light too.
viewtopic.php?t=9091
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dubcrazy8392
- Posts: 38
- Joined: Fri Jul 18, 2025 10:57 pm
- cars: -1981 6.0L LQ4 swapped C10 (aka lumpy)
-2000 silverado 2500 (daily work horse that does it with style)
Re: 4WD IPC indicator fix with 12587603 OS
that one i dont know, sorry.sparepartsblazer wrote: Wed Dec 10, 2025 4:46 amIm using an 07 Envoy IPC in mine.Actually i outlined how to do it with an 03 IPC running 15104999 calibration which can be found in the IPChammer program in this post. im sure with a hex comparison tool you can find the same bit pair in other year OS calibrations and turn off the ABS light too.
viewtopic.php?t=9091