Not sure which Gen 3 LS computer you have? The quickest way to identify it is by checking the connector colors, service number, and original application.

P01 ECU

Most commonly used in 1999–2002 Gen 3 GM applications.

Look for:

  • Red and blue connectors
  • Commonly found in early Gen 3 LS trucks and cars
  • Smaller 512 KB calibration
  • Frequently used for drive-by-cable LS swaps
  • Common service numbers include 12200411 and 12212156

P59 ECU

Most commonly used in 2003–2006 Gen 3 GM applications, with some later applications depending on the vehicle.

Look for:

  • Green and blue connectors
  • Larger 1 MB calibration
  • Common in later Gen 3 trucks and SUVs
  • Frequently used with drive-by-wire systems
  • Supports many later transmission, fan, and operating-system options

The easiest visual check

Red and blue connectors = usually P01

Green and blue connectors = usually P59

But connector colors are only the first step. The service number and calibration still need to match the engine, throttle system, transmission, and wiring harness.

Do not assume throttle type from the ECU alone

A P01 or P59 may be configured differently depending on the original vehicle and operating system.

Before ordering a tune, confirm:

  • ECU connector colors
  • Service number on the label
  • Drive-by-cable or drive-by-wire
  • Engine size and year
  • Transmission type
  • Injector information
  • MAF and MAP sensor setup

Using the wrong calibration can create problems with starting, throttle operation, transmission control, fans, gauges, or communication with other modules.

Need help identifying your ECU? Send a clear picture of the label and connectors along with your engine and transmission information.

Midgard Industries EFI Tuning
Longview, Texas
midgardind.com

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