Gen 3 LS Bench Harness (P01/P59)
For years I’ve read about people building bench harnesses which enable them to read and program PCMs (Powertrain Control Modules) on their workbench instead of having to swap them into a car. Additionally some folks in some automotive groups I am active in have developed programs and methods to accomplish things the commercial tools (such as HP Tuners) explicitly do not let you do.
Two examples of this:
- You can generally recover a “bricked” ECU unless the boot loader was overwritten during a failed flash.
- You can clone an ECU as long as your source and destination PCMs are the same hardware.
So, I ordered an OBDLink scan tool and began work on building my bench harness. The donor harness was hacked up junkyard style still attached to a 5.3L engine in a ~2002 Tahoe that rolled over on the interstate. Because of how they cut it up to remove the engine it was pretty useless but perfect for what I needed and it was free!
It is actually fairly simple to depin the harnesses. You unbolt them from the PCM, then remove the cover/guides (red) in first pic, then just release the fingers with a pick and push the wire out with another pick or small screwdriver. The only connectors you need on the PCM are: ground, battery power, switched power (ignition key), and serial data (how you actually read/write data).
With the confidence that it worked, I ordered a variable DC power supply and a few other things so I could build a self contained portable bench harness. When not in use, the PCM connector sticks to the Velcro strip. The Battery on/off switch simulates disconnecting the battery in the car while the ignition on/off switch simulates turning the ignition key on and off in the car.
