A junkyard PCM is one of the cheapest parts of an LS swap. It's also one of the easiest to get wrong. Grab the wrong computer, leave the connectors behind, or bring home one that sat in a flooded truck, and your cheap PCM can cost you a lot of time. Here's what to look for before you pay for it.

Know Which PCM You're Looking For

Most Gen 3 LS swaps use one of two computers:

  • P01 (red and blue connectors): Usually found in 1999–2002 GM trucks and SUVs. It's the common choice for drive-by-cable throttle setups.
  • P59 (green and blue connectors): Usually found in 2003–2007 GM trucks and SUVs. It's the common choice for drive-by-wire throttle setups.

Match the PCM to your throttle body. If you're running a cable throttle, look for a P01. If you're running an electronic throttle with a pedal, look for a P59. (For the full breakdown, see our P01 vs P59 guide.)

What to Check Before You Pull It

  • Look for water damage. Check the pins and the case for corrosion, green crust, or water lines. Skip anything from a truck that looks flooded.
  • Check the case. Pass on cracked cases, broken mounting tabs, or bent pins.
  • Photograph the label. Get a clear picture of the service number sticker. We need it to program the PCM correctly, and it's easy to scratch or peel off in shipping.
  • Write down the donor vehicle's info if you can see it. Year, model, and engine size help confirm what you have.

What to Pull With It

  • Both harness connectors, with plenty of wire. Cut the harness long if you're allowed to. Extra pigtails come in handy for repairs.
  • The drive-by-wire parts, if it's a DBW truck. Grab the pedal and throttle body, and check whether that truck used a separate throttle control (TAC) module. Some years did, and your swap will need it too.
  • Any sensors you still need. MAF, O2 sensors, and the coolant temp sensor are often cheaper here than new.

Why a Junkyard PCM Won't Run Your Swap As-Is

That computer is still set up for the truck it came out of. It has VATS (the anti-theft system) turned on, and it expects the original body control module, transmission, gear ratio, tire size, and sensors. Plug it into your swap and you'll usually get a no-start or an engine that fires and dies.

It needs to be programmed for your combination. VATS has to be turned off, and the displacement, transmission, fans, sensors, gear ratio, and tire size all need to be set correctly. If your engine has a cam or bigger injectors, the startup fueling and idle also need adjusting so it will actually start and idle.

Get It Programmed and Ready to Run

Once you've got your PCM, mail it to us and we'll program a startup/base tune built for your swap.

  • Stock / Near-Stock Base Tune: $100. VATS removal, transmission setup, fan controls, sensor setup, gear and tire correction, and a basic startup calibration.
  • Cammed / Modified Base Tune: $150. Everything above, plus injector data, a cam-based VE starting calibration, and idle and spark setup for modified engines.

Supports P01 drive-by-cable and P59 drive-by-wire PCMs. Typical turnaround is 2–3 business days after we receive it.

Order your mail-in LS swap base tune here →

Don't want to hunt through a junkyard? We also sell pre-programmed P01 and P59 PCMs with the tune already installed: $200 for stock engines and $250 for cammed engines. Contact us or call (430) 215-4536.