TAC module wiring from main harness
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Teching In
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TAC module wiring from main harness On my new Speartech harness for a 2004 Tahoe 5.3l, I removed the pins from the TAC harness plug coming off the main wiring harness that comes from ECM and plugs into the TAC module so I could pass them through the cowl. I took many pictures as to make sure I got the correct pin out alignment for reinstall. What I didn't realize is pin 3 and 15 are both black. Now I'm not sure how to figure out which goes into their correct slot. From what I gather pin 3 is for low reference signal and pin #15 is for ground. Any way to test this? Thank you for any help you can provide
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From: Ann Arbor, MI
In this post, the TAC uses 2 "low reference signal" for its 2 potentiometers. It also has a ground on pin 15. This is likely more like yours:
https://www.lsenginediy.com/gm-gen-i...uipment-guide/
As a different TAC, in this post the TAC uses 3 "low reference signal" for its 3 potentiometers. No ground is listed:
https://ls1tech.com/forums/conversio...e-pinouts.html
The purpose for 2 potentiometers is as a safety check. E.g. if one potentiometer failed and signalled WOT, you could be in a heap of trouble. When the 2 potentiometers don't agree the ECM goes into low throttle limp mode. I guess 3 potentiometers gives you even more safety.
In short, I think your pin 15 is ground and Pins 3 and 10 are Low Reference.
The difference is that a "low reference signal" goes to the circuit board in the ECU, which in turn goes to ground; in contrast a "Ground" may go to a ground connection on the engine or frame. If all your ground wires are good, there should be no difference.
However since the ECU is looking for "small" differences in the signal from the two potentiometers, I would make sure the Low Reference goes to the ECU.
If you are comfortable with an Ohm meter, it is easy to check which pins are which.
https://www.lsenginediy.com/gm-gen-i...uipment-guide/
As a different TAC, in this post the TAC uses 3 "low reference signal" for its 3 potentiometers. No ground is listed:
https://ls1tech.com/forums/conversio...e-pinouts.html
The purpose for 2 potentiometers is as a safety check. E.g. if one potentiometer failed and signalled WOT, you could be in a heap of trouble. When the 2 potentiometers don't agree the ECM goes into low throttle limp mode. I guess 3 potentiometers gives you even more safety.
In short, I think your pin 15 is ground and Pins 3 and 10 are Low Reference.
The difference is that a "low reference signal" goes to the circuit board in the ECU, which in turn goes to ground; in contrast a "Ground" may go to a ground connection on the engine or frame. If all your ground wires are good, there should be no difference.
However since the ECU is looking for "small" differences in the signal from the two potentiometers, I would make sure the Low Reference goes to the ECU.
If you are comfortable with an Ohm meter, it is easy to check which pins are which.
Thread Starter
Teching In
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Thank you for reply Ok, I did get the pins aligned correctly. Ohm meter made it a quick and easy fix.
However, I have one more hurttle to jump. As this LS1 truck motor is a custom build I used an LS3 throttle body that utilizes an X link to give proper signal to ECM. I am attempting to fire the motor for the first time since this build started 5-6 years ago. I am doing as many checks as possible prior to fueling and first attempt at firing. So, my last question before attempt firing, should I be able to operate the LS3 throttlre plate with foot pedal with the key in the on/run position. For that matter, should the gas feed operate the pedal in any ignition key position or does the throttle plate only energize after engine is running? Obviously this is a drive by wire. My thought was to attempt and see if I had signal from gas pedal TAC to throttle plate prior to fueling the tank for the first time. I didn't want to cause problems by actualting the gas feed while attempting to see if throttle plate would actuate by foot feed with gas flowin g from tank
However, I have one more hurttle to jump. As this LS1 truck motor is a custom build I used an LS3 throttle body that utilizes an X link to give proper signal to ECM. I am attempting to fire the motor for the first time since this build started 5-6 years ago. I am doing as many checks as possible prior to fueling and first attempt at firing. So, my last question before attempt firing, should I be able to operate the LS3 throttlre plate with foot pedal with the key in the on/run position. For that matter, should the gas feed operate the pedal in any ignition key position or does the throttle plate only energize after engine is running? Obviously this is a drive by wire. My thought was to attempt and see if I had signal from gas pedal TAC to throttle plate prior to fueling the tank for the first time. I didn't want to cause problems by actualting the gas feed while attempting to see if throttle plate would actuate by foot feed with gas flowin g from tank
Last edited by Ronf; Jul 15, 2023 at 05:20 PM.
