E38/T42 Bench Harness

[village_idiot]

Does anybody on here make one, or have one for sale?

Chime in on which on you personally use, and how you like it. (I would like to be able to flash the ECM/TCM both as if hooked to the vehicle, if possible)

So far, out of all of my searching, I like the Speartech or Bench-force the best of what I have seen. Any others out there I should look at?

I would attempt to make my own, but have not found a source on the connectors that are reasonable enough to justify building one vs the cost of just buying Speartech's unit... If you know where those are, send a link please?

[kevin87turbot]

I use the Speartech harnesses. They have been very reliable for bench tuning.

[village_idiot]

Thanks Kevin! Does it recognize an ECM/TCM combo as a "vehicle" when they're both hooked up? I've only bench flashed Gen3 stuff before. Also, if it is only an ECM hooked up, is it still 2 credits or not?

[kevin87turbot]

It reads them independently. It'll give you the OS for both the ECM and TCM, and you can read them together or seperately.

It's just 2 credits either way.

[Ben Charles]

Made my own, have a TCM connected to it for reading ECMS, can flash customer TCMs when provided..

But I have to have a TCM connected to my bench harness to work, not sure how John at speartech set up there bench harness?

[village_idiot]

To be clear on the credits thing...

If I hook to ECM only now to disable DOD and pay my 2 credits, then later I want to hook to the vehicle or ECM/TCM to make more adjustments...

When I paid 2 credits for ECM, does that cover TCM since same VIN? Will I have to pay again when it's time to adjust the TCM if done at different times? I feel like if same VIN, then same 2 credits but I've cost myself a lot of money over the years not asking questions I thought were obvious.

This might be a question for the guys at HPT, but figured you might have some insight. Thanks for your help!

[kevin87turbot]

I've made a few of the early model bench harnesses, but they are pretty basic.

The Speartech harness is pretty nice. It's set up for both T42 or T43 trans controllers...but you don't have to connect the TCM at all if you just want to flash an ECM.

[village_idiot]

Ben... I don't have hands on with one, but I do see that it is on a Y harness and the TCM part is removable from the harness with a connector. Their setup comes with E38 and T42/T43 harnesses..... So maybe I should call, and see if the only reason it's "removable" is just to switch between 42/43 or if you can actually remove it and program ECM only

EDIT - Kevin answered while I was typing. Thanks again!

[kevin87turbot]

To be clear on the credits thing...

If I hook to ECM only now to disable DOD and pay my 2 credits, then later I want to hook to the vehicle or ECM/TCM to make more adjustments...

When I paid 2 credits for ECM, does that cover TCM since same VIN? Will I have to pay again when it's time to adjust the TCM if done at different times? I feel like if same VIN, then same 2 credits but I've cost myself a lot of money over the years not asking questions I thought were obvious.

This might be a question for the guys at HPT, but figured you might have some insight. Thanks for your help!

Yes, you'll be covered when you install the ECM in the vehicle...it won't charge you anymore credits. It doesn't matter if you connect the TCM to the bench programming harness or not.

[kevin87turbot]

To be clear on the credits thing...

If I hook to ECM only now to disable DOD and pay my 2 credits, then later I want to hook to the vehicle or ECM/TCM to make more adjustments...

When I paid 2 credits for ECM, does that cover TCM since same VIN? Will I have to pay again when it's time to adjust the TCM if done at different times? I feel like if same VIN, then same 2 credits but I've cost myself a lot of money over the years not asking questions I thought were obvious.

This might be a question for the guys at HPT, but figured you might have some insight. Thanks for your help!

I've actually got an extra Speartech harness if you're interested...
Just DM me.

[village_idiot]

Yes, I am. Will DM now

[blindsquirrel]

Most vehicles have the CAN wiring so that the TCM is inline with the ECM - disconnect the TCM and the ECM no longer has a CAN connection to the DLC. Express vans used a different layout with the ECM/TCM on separate legs (for whatever reason GM put the ECM and TCM on opposite sides of the engine compartment on the Express). The ECM has a built-in terminating resistor that's internally connected, so it terminates itself automatically when it's at the end of a run. But the T42 can also be placed at the end of a run - it also has a terminating resistor inside, it's just not internally connected to anything. It has to be jumpered in to be in the circuit. It's at pins 15 & 19.

2008 Express GMLAN.png Suburban GMLAN ECM-TCM-BCM.png

[THE CHAD]

I use the Speartech harnesses. They have been very reliable for bench tuning.

...Yep agree ive used Speartech bench harnesses for years on all platforms and never ever had a issue