John McGraw

I went to fire up my LS2 conversion today, and the throttle does not work.
The engine runs, but throttle does not open. I finally got Autotap to read the DTC's, and the code was P2128 which is throttle pedal sensor failure.

Does anyone have a flow chart for troubleshooting the throttle pedal assy, so I can determine if it is the pedal or the wiring? It sure would be nice to know how it is supposed to work before I start changing parts. It is a brand-new harness and pedal From Speartech.


Regards, John McGraw

cam75w/ls1

iTrader: (2)

Hmmh, I know on the late model throttle by wire setups the there are actually 2 sometimes 3 throttle position sensors made into the gas pedal sensor. Usually when one fails it still operates the throttle with the exception of check engine light for a code for one of the tps's internally. I also have experienced no throttle at all symptoms and it was the pedal assembly or no power to the pedal. Ok, I just checked the wiring for a 2005 vette w/ APP it shows that code you pulled could be voltage problem. Make sure your APP is getting 5 volts reference and not 12. On the GM's they are showing 2 sensors on your APP. Sensor 1 increases from 1 volts to 2.5volts when you step on the gas. Sensor 2 goes from 4 volts to 1 volts when you step on the gas. Problem is I don't know if the wiring is the same colors as this schematic but hopefully it might point you in the right direction.

John McGraw

Thanks, that helps a lot! With only 6 wires, I should be able to figure out what is what. If I get 5 V on the two wires, and low reference on the two others, then I can pretty much bet that the acc pedal unit is bad. I will have to look, but I think that both my GM trucks use the same pedal unit. I might have to swap one out off of one of my trucks to proof it.


Regards, John McGraw

John McGraw

Well, I just went out and crawled under the dash, (no small feat for a guy of 250lbs and a C2 Corvette), and I had 2 wires with 5 volt reference, and 2 wires with ground reference, so I would say that it is a safe bet that the pedal is bad. I am going to pull the pedal and try and figure out if the right wires are on the right pin, but without the schematic, it may be tough.
I will look at the truck tomorrow, and if it is the same, i will pull it off and try it.


Thanks, John McGraw

John McGraw

It just gets stranger and stranger! My wiring was the same color code as the one you posted. The wires are landed on the correct pins, the impedance of both sensors in the ECM is about the same (about 250 k ohms, which seems about right), the pots in both APP sensors seem to be very linear, and move in opposite directions as they should, but the throttle still does not operate.
I know that the TAC motor is good, as it does it's little jog when you turn the key on. I am just about to pull my hair out! I have pissed away all day on this problem and am no closer to knowing what is wrong. I am going down to 6th street and drink some beer tonight and hit it again tomorrow when I am fresh.


Thanks John McGraw

John McGraw

Well, went out this morning, plugged the pedal back in, and it worked like a champ! It must have been a bad connection in the connector at the pedal.
The engine runs like a scalded cat! The exhaust is a little louder than I wanted, but I am still so happy, that it will take at least a couple of days to get this stupid grin off my face!


Regards, John McGraw

cam75w/ls1

iTrader: (2)

Hmmh, wonder if the computer didn't see the added hardware?? Well I'm glad it's going now. At least the conversion works! So, what's the conversion in??

John McGraw

Yea, it was strange! Only thing I can figure was that I did not have the plug fully engaged in the pedal. Thanks a lot for the schematic, without it I would have been still chasing my tail! At least is allowed me to prove that there was nothing wrong with the wiring, which was a big step.

The conversion is a 65 Corvette convertible with a tube chassis, C5 front suspension, and C4 rear suspension. It has a 05 LS2 with a 4L65E trans.

It is a companion for my 59 Corvette with same frame setup and a LS1 engine. I wouldn't want it to get lonely when I am not around.
The 59 is a great car, but I can't really drive it with the top up, so I never take it on long trips. At least I will be able to drive with the top up and the A/C on in the 65!

Here is a some pic albums with my projects.

http://www.villagephotos.com/pubgallery.asp?id_=339303

Come by my shop some weekend and shoot the bull. I am over on the SW side of town. Give me a call on my cell 663-2327

Regards, John McGraw

cam75w/ls1

iTrader: (2)

I'll have to check the place out since we're building hybrids. I'm building a 40x60 shop right now w/ a paint booth on the outside. I've been buying Mustangs,Camaros,and Rx-7s. I've already finished a 75 Camaro w/ LS1. Two RX-7s w/ Mustang Gt drivetrains. I have a 69 R code fastback Mustang right now that will be the first build in the new shop. It'll get a 2007 GT500 drivetrain w/ blower when one comes availible. Right now I'm doing the 408 stroker in my S10. It's a 6.0L out of a 2005 HD2500 stroked w/ Callies internals. The L92 heads w/ carbed intake modified to work w/ fuel injection. I'm still in progress on it and won't be finished till April. I'm rebuilding my "tow" truck so I have alot on my plate. Nice to see you're into vettes. I used to work for Corvette Country awhile back and have Vettes of my own. Looking for 2005-2007 as we speak. I'll keep your number and give you a call after the holidays. If you need to call me then you can reach me at 512-331-9797. That's my work number and can call anytime. Thanks,
Robby(cam75w/ls1)