2002 5.3 DBW issues

[t-tung]

Got a few issues. Using a PSI harness and PSI brake switch. Engine fires and idles fine. It will rev fine with the foot off the brake but not with the brake pedal depressed. Like if I wanted to do a power brake, I wouldn't be able to. That is the minor problem but I think it may be tied to the big problem. I hooked up a Snap-On scanner to it and I'm not getting any voltage readings in the TAC data screen and its throwing a P0122 code. We verified all 3 5-volt signals going into the TAC from the pedal (2 0-5 when depressing pedal and 1 5-0 when depressing pedal.) So the pedal is working. We checked the 6-wire TPS on the throttle body; all checked out fine. Check the 2-wire connector (brown in A; yellow in B) throttle body connector. It works. I'm not sure what else to look at. Seems like there's something out of place between the TAC and the PCM. On the scanner when looking at engine data, it shows when you depress and release the brake pedal. Doesn't show up on the TAC data screen. I don't know if there's something that I'VE got wired wrong or if maybe one of the wires between the TAC and the PCM are in the wrong spot.
I've tried another pedal and TAC module from an 03 and have seen no difference.

What am I missing here??

[t-tung]

Everything worked perfectly before we pulled it

[BR3W CITY]

Locate the wire your using for Ground off the TAC, and separate it from any other grounds. Connect it to its own solid ground, and see if anything improves. Mine was throwing intermittent codes related to the DBW system (also a 2002/2003), and improving the ground and re-seating all the plugs helped. I'd suggest unplugging the battery before doing this so its "starting fresh" on the new ground and has a chance before popping any existing codes.

Where is your TAC located? If it were getting excess heat/flex/vibration i could see problems. The PCB boards inside can break solder joints if they are physically flexed.

*I actually had a very weird issue with the U0107 code possibly being caused by MASS magnetic field interference, which is hard to believe, but I have a theory

[t-tung]

Alright will do. I THINK the ground for the TAC comes from PSI bundled together with 3 other grounds so what you're saying makes sense and may be the problem. I've got two good grounds going from the block to the frame, one solid one going from the block to the firewall and another solid one going from the frame to the firewall so I feel pretty confident I'm well grounded. I'll give anything a shot right now

[t-tung]

TAC isn't permanently mounted yet. I haven't been driving it or anything. I just got it fired up for the first time the past weekend

[ls1nova71]

So are you saying the throttle works when it isnt in gear, but doesnt when it is in gear? Is the pedal going dead and not doing anything? Also, you cant put a 2003 TAC on a 2002 engine unless you have the matching throttle body, pedal and PCM. Since you say it was working before, did you have the whole truck or did you get it at a salvage yard? Your TAC should be the all plastic one, and your throttle body should have two plugs, does it? Also, who tuned it? Are you sure it has the correct OS?

[t-tung]

Originally Posted by ls1nova71

So are you saying the throttle works when it isnt in gear, but doesnt when it is in gear? Is the pedal going dead and not doing anything? Also, you cant put a 2003 TAC on a 2002 engine unless you have the matching throttle body, pedal and PCM. Since you say it was working before, did you have the whole truck or did you get it at a salvage yard? Your TAC should be the all plastic one, and your throttle body should have two plugs, does it? Also, who tuned it? Are you sure it has the correct OS?

I bought a whole, running 2002 Tahoe and pulled everything I wanted off of it. I haven't put it in gear, only messed with the brake switch. With the brake pedal depressed (lights on), the gas pedal won't work. I've even revved it up to 1200rpms, depressed the brake pedal and it will "kill" the throttle back down to an idle. I tried a 2003 TAC and pedal (in every combination with the stock pieces) just to see if anything would change and it didn't. I didn't think about a 2003 TAC not working with a 2002. So I guess if the 2002 TAC somehow went bad, the 2003 wouldn't help me anyways.

Throttle body has a 2-pin on the passenger's side and 6-pin TPS on the DRIVER's side. Like I said, everything was in perfect driving condition when it was pulled so the components SHOULD be good.

[t-tung]

Texas Speed & Performance did the tune

[ls1nova71]

Ok, I see now. That is odd that the brake switch would kill the throttle, never seen that before. How is your brake switch wired? I wonder if it was wired backwards and tried locking the converter when the brake pedal was depressed?

[t-tung]

Purple wire from PCM gets power with foot off brake. Yellow wire from PCM get power with brake pedal depressed. Both per PSI wiring diagrams for the harness and brake light switch

[t-tung]

Still having this problem with the brake "killing" the throttle and it's driving me crazy. Still have the P0122 error and data from TAC still isn't showing up on the scanner. Any ideas? We thought the yellow wires (pin 6 and 16) on the TAC module may have been switched accidentally bu they checked out. Pulling my hair out here.

[ls1nova71]

If it ran fine before the swap, then you need to look at what was changed. In this case its the harness, and maybe the tune. Have you asked PSI about it? Also have you tried unhooking the wires to the brake switch to see if it would power brake then?

[t-tung]

I've been on the phone off and on with PSI trying to troubleshoot it. If I disconnected the yellow wire from the brake switch it would surely power-brake because it won't be getting a signal at all. Their instructions specifically say it has to get 12v power when breaks are applied though. Says harm to your transmission can come from not being hooked up. Then on their instructions for the brakelight switch it says the yellow wire is for Gen IV only so idkwtf to do.

[t-tung]

For reference here is the brake-light switch I have http://www.psiconversion.com/tech_ar...STRUCTIONS.pdf

And here is the harness I have http://psiconversion.com/tech_articl...structions.pdf
Page 11 has the wire breakdown