928vette

I've read through other similar posts, but they did not seem to help.

Problem:
The Drive By Wire Accelerator Pedal (APP) does not function properly on my 2001 Corvette LS1 hybrid swap.
Here is a good description of Chevy Drive-by-wire: http://chevythunder.com/drive_by_wire.htm

Overview:
Accelerator Pedal (APP) assembly, Throttle Actuator Controller (TAC), PCM, and engine are from the same 2001 Corvette (I pulled them all myself). The car had been rolled so the top was smashed, no significant front-end damage.
I do not have the Body Control Module (BCM).
I am using the original corvette wiring harness and fuse box. I have attempted to apply the correct 12V and grounds. I have grounded pin 15 of the TAC in particular.
When the throttle is manually opened/closed, the scanner displays the correct position.
The APP has never registered anything other than zero% in my scanner program (HPTuners).
When the accelerator pedal is pressed, nothing happens/changes.

Troubleshooting:
I measured the voltages between the APP and the TAC and they seemed to me to meet the requirements identified in one of the DTC descriptions:
There are 3 APP circuits in the pedal, here are the expected ranges from pedal out to pedal max:
· APP 1 Pin F(dkblu): Increases from less than 1.1V to greater than 2.1V
· APP 2 Pin C(ltblu): Decreases from greater than 3.9V to less than 2.9V
· APP 3 Pin K(dkgrn): Decreases from greater than 3.2V to less than 3.1V
I measured the values at the TAC (using an ohm meter and a safety pin inserted into each wire) and the values were:
APP 1: 0.46V to 2.65V
APP 2: 4.5V to 2.28V
APP 3: 4.1V to 2.86V
These look perfect to me, I think the APP is working perfectly.

What works:
The APP appears to have the correct voltages as the pedal is depressed.
The TAC communicates properly with the PCM.
The Throttle Position Sensor works properly and reports the correct value to the TAC (and scanner).
The TAC reports the correct throttle position to the PCM even when the throttle is moved manually.

What doesn’t work:
The APP always registers zero%.
The throttle never physically moves.

Questions and things to try:
Is the throttle supposed to cycle open and close at engine turn on? This one doesn’t, it has never moved except manually. If it is supposed to move, I will measure the voltages on the throttle control (pins 8 and 16) to see if they change at startup. There is no ‘start’ signal going to the PCM, I assume it knows it is starting based on RPM??
Can I apply voltage to the throttle to see if it opens? If I apply 12V, will it open or is that too much voltage?
I have done nothing with the cruise control inputs to the TAC, I assume that they should have no effect on reading the pedal position. Is it possible that they need to be grounded so they appear off?
Is there any setting or anything the PCM might need that would cause this problem?

Summary:
It appears to me that the TAC is broken, but I hate to spend $350 only to find out I’m wrong. I just replaced the TAC connector, just in case. I simply don’t have enough experience to be confident that the APP isn’t correctly reported because of a problem in the throttle control motor or something that the PCM needs and is not getting. Any help is appreciated. Hopefully, some of the info I’ve produced here will be helpful to others in the future.

928vette

With the key on, but the engine not running, should I expect that pressing the accelerator pedal would cause the throttle to open and close? On a drive by cable system, of course it would, but with drive by wire, I can imagine that it might not.

99MUSTANG5.3L

The only thing I can suggest is cleaning the throttle body and make sure that the blade isn't getting hung up anywhere. I've heard of similar problems caused by the throttle blade being hung up on the housing.

garys 68

iTrader: (1)

Where did the pedal to TAC harness come from? There are some changes between years. Double check the wiring from the vehicle/year specific schematic, not the link you posted.
On my 02 trucj DBW, the TB moves with key on, engine not running.

928vette

I built my own cable, separate from the harness. I cut the original 10-pin connectors from inside the engine compartment and inside the car. The connectors appear to be identical on both ends. I then spliced-in new wires to 9 of the 10 original wires (1 is plugged/not used). I verified via the schematics that the pins are 1-1 (pinA goes to pinA, pinB goes to pinB, etc.). I used an ohm meter to ensure continuity for each pin. I have the shop manuals for my exact vehicle, which is what I use, the link above was just for convenience of others. I am going to check it all again against the schematic and also disconnect it to make sure that the TAC/PCM produces the expected DTC. The difficulty here is that I have no knowledge as to what happens internally in the TAC.
Many thanks for your suggestions.

garys 68

iTrader: (1)

On my 02 TAC and pedal, E connects to J and J to E.
Double check your schematic.

928vette

I checked the schematic and the pins are definitely 1-1. It shows pin E going to pin E and pin J going to pin J. If they were supposed to be different, I don't think that the voltages I checked could have been correct for the pedal out and depressed. I also checked the wire colors on each connector-end, assuming that, if they crossed E/J J/E, that the colors would be different, but the wire colors were the same.
If I remember correctly, the '01 and '02 are almost identical engines, right? Does your schematic actually show the E-to-J? I may just swap the pins for lack of anything better to do, if my schematic is correct, then it won't hurt anything.

fptransport

just one question, did you connect the pedal after connecting the battery power to the pcm,,
I had a problem on mine, since I first connected the battery power to pcm, then I connected the gas pedal to the module, and the pcm couldnt/wouldnt read it, after I disconnected the battery and reconnected it it worked fine..\
hope this helps

busta9876

iTrader: (3)

you stated "When the throttle is manually opened/closed, the scanner displays the correct position."

Normally, when the key is on (as would be required to read data) the TAC module will command the throttle at a near closed position. If something tried to physically move the blade, you would hear the motor push against your finger as your tried to move the blade. A properly powered up TAC system will require a lot of force to move the blade from its home position. If it just pushed open easy, something is wrong, maybe a code set, etc. Does engine run?

have you scanned it for codes?

garys 68

iTrader: (1)

My 02 LQ9 schematic shows E to J and J to E. The harness I bought aftermarket is wired E to J and J to E. Worked perfect the first time. Confirmed in several schematics on LS1 swap FAQ.
But I also found a 99 vette schematic there that showed J to J, and E to E.

928vette

Thanks to everyone for their help and suggestions. I found the problem - the throttle control motor was bad.
Troubleshooting the accelerator problem was a challenge because:
1) The PID that is supposed to display the accelerator position does not work if the throttle control motor (on the throttle body) is bad. I would have thought that the TAC would correctly display the actual accelerator pedal position at all times, but this is not the case. It appears that, if the TAC fails to control the throttle motor at start-up, then it fails to provide the accelerator position from then on.
2) The DTC "P1516" occurs when the ignition is turned on, but if the DTC's are cleared, it does not reappear.
3) It initially appears that an accelerator problem must be either the accelerator pedal or the TAC module, it is not clear until you dig into the design that it is a closed-loop system consisting of the accelearator pedal, TAC, throttle control motor, and throttle sensor.

TurboGoKart

iTrader: (1)

My hybrid is doing the exact same thing right now, but with a P1518, that WON'T clear.


Question about your throttle motor operation, when I turn my key on, I can hear a faint clicking coming from that motor. Does your motor do this now that it's replaced and works? I also have no accelerator operation.


I'm wondering if that just needs to be replaced too before I pony up and get a new TAC lol.

928vette

In regards to your clicking question, what should happen is - when you first turn on the key, the butterfly on the throttle body should open and close real quick, not exactly clicking, but just a cycling open and closed.

The connector I was working on was between the accelerator and the TAC so is different than your issue. P1518 is related to the cable between the PCM and the TAC. Before I spent any money, I would find the pin on the TAC and the pin on the PCM that has the serial data and use a meter to make sure that the wire isn't open in the cable (there may be two wires, not sure). If the wire is good then clean both connectors and plugs then plug it in. Make sure that you have good grounds on all of the PCM ground lines and all of the TAC ground lines. Also, make sure you have at least 12V on your battery. If that all works, then probably a new TAC is needed. Wish I had a spare one to loan you.

928vette

In regards to your clicking question, what should happen is - when you first turn on the key, the butterfly on the throttle body should open and close real quick, not exactly clicking, but just a cycling open and closed.

The connector I was working on was between the accelerator and the TAC so is different than your issue. P1518 is related to the cable between the PCM and the TAC. Before I spent any money, I would find the pin on the TAC and the pin on the PCM that has the serial data and use a meter to make sure that the wire isn't open in the cable (there may be two wires, not sure). If the wire is good then clean both connectors and plugs then plug it in. Make sure that you have good grounds on all of the PCM ground lines and all of the TAC ground lines. Also, make sure you have at least 12V on your battery. If that all works, then probably a new TAC is needed. Wish I had a spare one to loan you.

Jim_PA

iTrader: (9)

Mine does, but it's an '04 truck setup.

TurboGoKart

iTrader: (1)

No worries! I just bought one for $180. So if it doesn't work, I'll just resell it at least just to get what I paid for it. Thanks for the tips on the 2 serial data circuits. I will check them again as well as the grounds. Check, double check, triple check, quad check....etc.

TurboGoKart

iTrader: (1)

Grounds are good. I just depinned the serial data wires at the 16-pin plug on the TAC and the PCM, and re-pinned it straight from the PCM to the TAC (to make sure nothing was shorting out/wires interfering with each other) and still no go. My voltage for those two wires is correct. We'll see what happens when the new TAC gets here. If it doesn't work I suppose I'll just switch to drive by cable.

Vetteman61

iTrader: (1)

Man, thank you so much for this comment. I had my computer updated and the pedal still wasn't working right. I happened to read your post before I started tearing everything down to test again and this was the problem. Had to have the battery hooked up after the pedal wires were hooked up.

G Atsma

An 8-year old thread can come in handy at times, huh? Glad it helped!

Vetteman61

iTrader: (1)

Most definitely