DBW not working, troubleshooting??

[imsuchaman55]

I have a 2001 5.3 with DBW, and we have gotten it to fire up, but we are getting zero response from the fuel pedal. Is there a way to test any of the plugs on the throttle body, fuel pedal, or TAC module to trouble shoot what could be the problem? I see on the schematics that some wires are 5v reference, is there a way to test any of these? Any help would be greatly appreciated
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[ls1nova71]

It's a 2001 with DBW? They made them, but they were only in the high end trucks like Escalades and Denalis, so finding parts for them isn't as easy as the newer ones, they use a throttle body that looks alot like a Corvette, and the TAC module is all plastic, is that what you have?. Do you have the correct TAC and matching pedal? And the PCM to match all three? Other than that you can check for power and ground, but beyond that you'll most likley need a scanner.

[imsuchaman55]

Originally Posted by ls1nova71

It's a 2001 with DBW? They made them, but they were only in the high end trucks like Escalades and Denalis, so finding parts for them isn't as easy as the newer ones, they use a throttle body that looks alot like a Corvette, and the TAC module is all plastic, is that what you have?. Do you have the correct TAC and matching pedal? And the PCM to match all three? Other than that you can check for power and ground, but beyond that you'll most likley need a scanner.

Yes it is a 2001 out of a gmc sierra. The engine, pcm pedal and TAC are all from the same truck supposedly. The salvage yard said they are from the same truck, but who knows. The TAC is the plastic one, and throttle body does look like a corvette one. I have been trying to track down info on what pins are power and ground for the plugs in the dbw system. I am thinking the tune I had done on the PCM could be the problem also. I am tempted to get a cable throttle body and get the pcm reflashed with a cable tune and being done with it, but am pretty aggivated since I've already mounted the fuel pedal and sealed the wiring harness all up
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[imsuchaman55]

I also have a OBDII plug I will be wiring up, will the code reader be able to tell me what the problem is? I have a friend that has a code reader. Thanks for your help
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[ls1nova71]

The pink wire pin 7 of the C1 connector (harness side that plugs into the TAC, not the one going to the pedal) is power, make sure you have ignition power on it, and pin 16 black/white is the ground. Also you could check for continuity between pin 8 brown and A on the throttle body and pin 16 and B on the throttle body.

[BR3W CITY]

Mine threw a code when it had Tac/pedal mistmatch problems. Honestly the only problem I see people have with DBW is usually mistmatched components or the occasional bad tac or burned out (i think) potentiometer on the pedal. Then look for the stupid stuff like pinched wires, missing pins in the clip etc

[imsuchaman55]

When I connect the battery, with key off, the throttle body makes an electric noise, like a quiet hum, but no response from the pedal. I think I will go to the salvage yard and get a cable throttle body, remove my harness and thin it out some more. I'm not using cruise control, so the dbw doesn't seem worth the hassle. Its just very frustrating that you make sure you get everything from the same truck, and still have issues like this. Oh well!!
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[BR3W CITY]

What your describing sounds exactly like an equipment mis-match. When you start, it will hum and cycle the tb to proof the sensors. After that it will either not respond to input, or respond once then lock out.
Can you post a pic of your pedal?

[imsuchaman55]

I can try to get a pic of it. Im at work but I can get someone at the shop to crawl under there and get a pic of it. When the engine showed up from the junk yard, it had the TAC still connected to the harness, but the fuel padal was not there. They then sent the pedal over later. Im thinking maybe they sent it from a different truck? Also, I had my PCM flashed a few weeks ago, and when I told them it was a 2001, they didnt know it was a dbw, so I took it back this week and they reflashed it with a 2001 dbw program, could this also be my problem? Or does it sound mainly like item mismatch?

[ls1nova71]

Sounds like mismatched parts still, but also make sure they flashed it with a 2001 tune, if they used the more common 03 and up, it wont work. Since you hear a sound coming from the TB it sounds like its working, did you verify power and ground at the TAC?
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[ls1nova71]

One more thing, if that checks out, try wiggling the wires about 6 inches or so away from the throttle body, that's about where they will break. The breaks will be in the insulation so you probably wont see them, but moving the wires around will make continuity at times so you may find a problem that way.
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[imsuchaman55]

Originally Posted by ls1nova71

Sounds like mismatched parts still, but also make sure they flashed it with a 2001 tune, if they used the more common 03 and up, it wont work. Since you hear a sound coming from the TB it sounds like its working, did you verify power and ground at the TAC?
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I havent had a chance to check anything yet because Ive been at work. I will try to get by the shop after work and check though. I put in a call to the salvage yard here in town that I got the pedal from to have them double check to see if the fuel pedal that goes with this engine/pcm is still in that truck. I have a feeling that when we called to get the pedal, the guy in the yard just went out and grabbed the closest on around, and it was a 03 and up.

Originally Posted by ls1nova71

One more thing, if that checks out, try wiggling the wires about 6 inches or so away from the throttle body, that's about where they will break. The breaks will be in the insulation so you probably wont see them, but moving the wires around will make continuity at times so you may find a problem that way.Posted via Mobile Device

I checked all of the wires when I re-did the harness and before I bundled it all back up and didnt notice any breaks, but I can double check.

[Daaaanz67]

I just got my computer flashed by bill at forced fed, I had him verify the vin for my computer you should check if yours is on file at his shop on his lap top. Maybe you could find some part number on the pedal get the vin from bill call a dealer to double check for correct pedal. I would try to keep the dbw if it's not to difficult .
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[imsuchaman55]

Originally Posted by ls1nova71

The pink wire pin 7 of the C1 connector (harness side that plugs into the TAC, not the one going to the pedal) is power, make sure you have ignition power on it, and pin 16 black/white is the ground. Also you could check for continuity between pin 8 brown and A on the throttle body and pin 16 and B on the throttle body.

I will check and update

[imsuchaman55]

Originally Posted by Daaaanz67

I just got my computer flashed by bill at forced fed, I had him verify the vin for my computer you should check if yours is on file at his shop on his lap top. Maybe you could find some part number on the pedal get the vin from bill call a dealer to double check for correct pedal. I would try to keep the dbw if it's not to difficult .
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I'm glad you were able to get bill to help you out, he's a great guy to deal with.

We had a friend with a code reader come by tonite. Figured out everything was good but the fuel pedal. It was showing 2 of 3 channels putting out over 100% of the voltage they were supposed to without the pedal being touched. And only 1 channel showing any change when pressed. Thank god for his code reader and laptop with alldata. Thank you guys for helping!
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[imsuchaman55]

I wanted to post this for anyone that is having this issue in the future. This is what we found to be wrong by using the code reader.

First we found these schematics, and double checked all pin locations.



I found all schematics and pinouts on this page, but cant copy the images to post here. http://www.chevythunder.com/drive_by_wire.htm

On TAC plug, C2. Pink, Pin 7 had ignition voltage, and black/White, pin 15 had ground.
Checked continuity on circuits between TAC plug C2 and Throttle body plug. All wire showed continuity and in proper plug location.
Also checked for continuity between TAC plug C2 and Throttle actuator control (TAC) motor plug, and all were correct.

So we knew were were getting power and ground from the PCM. and wiring between TAC and throttle body were correct. Next, we checked continuity and pin location on TAC plug C1 and Accelerator Pedal Position (APP) sensor. All pins were in correct location and showed continuity.

Then plugged the TAC plug into the TAC, and checked the 3 5v reference pins at the APP sensor plug to make sure we were getting 5v from the TAC. All 3 showed to be correct. Plugged back into pedal.

We then removed plug on the TAC motor and checked for any grounding while pedal was depressed. No grounding showed the wiring to the TAC motor was good.

We then connected everything back up, plugged in code reader, and started the truck.

We found this info on alldata, so I copied it here

"Circuit Description
The Accelerator Pedal Position (APP) sensor is mounted on the accelerator pedal assembly. The sensor is actually three individual Accelerator Pedal Position sensors within one housing. Three separate signal, ground and 5.0 volt reference circuits connect the Accelerator Pedal Position Sensor assembly and the Throttle Actuator Control (TAC) Module. Each sensor has a unique functionality. The APP sensor 1 signal increases as the accelerator pedal is depressed, from below 1.1 volt at 0% pedal travel (pedal at rest) to above 2.1 volts at 100% pedal travel (pedal fully depressed). The APP sensor 2 signal decreases from above 3.9 volts at 0% pedal travel to below 2.9 volts at 100% pedal travel. The APP sensor 3 signal decreases from above 3.2 volts at 0% pedal travel to below 3.1 volts at 100% pedal travel. Observe that the signal circuits for APP Sensor 2 and APP Sensor 3 pull up to 5.0 volts and the APP Sensor 1 signal circuit pull to ground within the TAC Module."

With the truck idling, and no throttle input, The code reader showed that sensor 1 signal at 5 volts and showing 100% pedal, sensor 2 showed 4.1 volts and 0% pedal, and sensor 3 showed 4.8 volts and 100% pedal. When the pedal was depressed, sensor 1 & 3 showed no change in voltage or % pedal. Sensor 2 seemed to change the voltage and pedal % correctly.

From this info we narrowed it down to either being the wrong pedal, or the APP is toasted.

I dont know if this will be of any help to anyone else, but I figured I would post for anyone with future similar problems.

[OldCreek]

Instead of getting another pedal assembly from the junk auto salvage, you should order a new APP sensor online or from the parts store.

I had/have a similar issue, intermittently. I may try to change the TAC module, also. I've already changed the app sensor once.

[BR3W CITY]

if he has the wrong year pedal , it doesn't matter if his sensor is bad. Some have 2 sensors that read opposite resistance sweeps, so if his tac looks for 1 signal and gets 2 or vice versa it won't work correctly.

[OldCreek]

Copy that.

However, on my pedal the sensor can be unbolted from the pedal assembly. I would assume the appropriate sensor from the correct year/model could bolt into it's place? The wiring plugs into the sensor and not the pedal.

Depending on the year/model, maybe one sensor can not be substituted for another if the plug and mounting holes are different.

...maybe I just need to go down and look at my assembly.

[BR3W CITY]

the pedal shapes and mounting bases are different, the metal pedal you can remove the sensor from the bracket. I don't know if you can do that as the sensor looks to be in the plastic box that is part of the plastic cast pedal.

Another thing....I can't find much info on a 2001 with DBW....are we assuming that is uses the 02-05 truck setup? Or maybe it uses the 98+ corvette dbw, as it was already in production. The pins on the connectors are the same pretty much, but the tac is different.

I was checking out this
http://www.chevythunder.com/drive_by_wire.htm

Interesting info with diagrams, may or may not help.

[farmtrucks]

i had this problem - I swapped the pedal (same kind) and it fixed it - I think mine could have been out in the weather to long. I thought it could only be 3 things - TAC, pedal, throttle body -- luckily the first thing I swapped fixed the problem. Find a buddy that has a stock pick-up and start swapping parts.

[imsuchaman55]

We ended up getting another pedal and plug from the Salvage yard. The new pedal with the old plug did not work, but we changed the plug with the new pedal and it worked fine. Then we put the new plug with the old pedal and it didnt work. Weird, maybe the plug and the pedal was bad.

[BR3W CITY]

stranger things have happened! Glad you got it working.