blainemaxwell

I just got my jet boat running with 2004 LQ4. The Engine will start and idle fine. The ETC won't work, as soon as I turn the key ON the throttle blade goes closed and back to 19% and sets the following codes.
[PCM] P1125 - APP System (SES) (Pending) (Old) (History) (Current) (Immature)
[PCM] P1516 - Throttle Actuator Control (TAC) Module Throttle Actuator Position Performance (History) (Immature)
[PCM] P2120 - Throttle/Pedal Position Sensor/Switch D Circuit (Pending) (Old) (History) (Current) (Immature)
[PCM] P2125 - Throttle/Pedal Position Sensor/Switch E Circuit (Pending) (Old) (History) (Current) (Immature)
The accelerator pedal has no effect on the throttle blade.
All the components are from the same donor truck. I tried a different APP sensor and no change. I have read and searched lots of threads and haven't found any solution.................. Any Ideas....?

busta9876

iTrader: (3)

The APP sensor needs to be rotated slightly off its resting position when the pedal is released. I ran into this with a gas pedal I had, kept getting APP codes. The pedal was modified to fit the vehicle, so I first tested it with another complete pedal assembly I had, and it worked fine, so I pulled the working APP sensor off the extra pedal I had, and put the sensor on the modified pedal I had already installed in the vehicle, and the same codes came back. There is no adjustment to the sensor, so you will need to make a stop for the gas pedal when it returns.

You may notice that only 1/2 the travel of an APP makes throttle go wide open. I had one install that the gas pedal was just too high, and uncomfortable to drive. I was able to adjust the stop on the throttle, and moved the gas pedal 1/2 way down, and then used the bottom half of the travel. The TAC/PCM learns minimum position after a few key cycles.

Good luck, please report back what you find.

psiconversion

iTrader: (5)

Are you still running the base Truck Tune?

Jon
PSI

blainemaxwell

The only thing I've changed from the base tune is VATS disabled and all inapplicable DTC's. I will try the pedal @ rest adjustment tonight. The weird thing is I unbolted the complete pedal assembly out of my 2003 GMC daily driver and plugged it in and it did not change the problem. Maybe it did not like the at rest value of that pedal either? BTW I use HP Tuners. I will try some things tonight, Thanks Guys.

psiconversion

iTrader: (5)

Is the TCC/Brake switch wire hooked up and is the check engine light hooked up?

Jon
PSI

blainemaxwell

Do you mean Blue pin-33, and Green pin-46? No and no. Also what do I do with Green pin-50? Will I need a VSS?

psiconversion

iTrader: (5)

Hook up your check engine light and the brake switch wire. Throttle should work. You shouldnt need a vss.

Jon
PSI

blainemaxwell

Can I just use any 12vdc lamp on the MIL output?

blainemaxwell

Ok I hooked up a MIL negative from PCM positive from constant power, TCC wire to constant positive, and pin-6 from TAC (brake lamp proof) through resistance to ground. The MIL works as I can command it On or OFF. I can clear DTC's but they instantly return.


[PCM] P1125 - APP System (SES) (Pending) (Old) (History) (Current) (Immature)
[PCM] P2120 - Throttle/Pedal Position Sensor/Switch D Circuit (Pending) (Old) (History) (Current) (Immature)
[PCM] P2125 - Throttle/Pedal Position Sensor/Switch E Circuit (Pending) (Old) (History) (Current) (Immature)

busta9876

iTrader: (3)

per alldata

P2120
Sets when APP sensor 1 voltage is below 0.24v or above 4.49v
or
5 volt reference circuit is less then 4.54v or more then 5.21v

P2125
This code is the same as P2120, except deals with APP sensor 2 circuit.

P1125 sets when the difference between APP 1 and APP 2 are more then a predicted value.


Diagnostic flow chart shows check P2120, P2125 before dealing with P1125, whatever is causing the 212x codes, is likely also causing the P1125.

You need to find the PID for raw APP sensor voltage on HP Tuners. See what the voltage reads, and see if it falls in the range listed above.

You may also check with a digital volt meter, attached is schematic for 2004 drive by wire pedal to tac module wiring.

Also, make sure your gas pedal harness is wired correct, note that E & J are crossed at each end, all the other pins are A to A, B to B and so on.

Also, I've noticed the 03+ truck pedal harnesses only have APP 1 and APP 2, even though the schematics show APP 3, the harness should only have 6 wire on it.

blainemaxwell

Well no luck. I have verified positive 5 volts on reference wires both sensor 1 and 2 low reference to ground is good on sensor 1 and 2. I checked continuity on serial data wires from PCM to TAC module. All values were checked with DMM @ APP end of harness. I can't see voltage through HP Tuners scanner????? I also checked resistance from TAC module end of harness to APP. Both sensor 1 and 2 have nice sweep with pedal but sensor 2 resistance is consistently about 1100 ohms lower than sensor 1. Both sensor circuits ( 5 volt to signal ) have higher resistance at rest than full throttle. I can't prove the TAC module is bad so I hate to just throw parts at it. And like I said ALL the components came from the same donor truck. What gives????

psiconversion

iTrader: (5)

Pin 6 goes to switched power through brake switch. Same a TCC clutch.

Jon
PSI

blainemaxwell

I've tried pin 6 to ground, stop lamp resistance to ground, and switched power. Maybe I do have a bad TAC module?

ls1_chevelle

iTrader: (9)

when I first fired my car with a dbw setup it woudl reset the the TB like you say and just idle all damn day but no input would get detected. Never scanner for codes but it turned out to be a dead TB.

try and get your hands on another TB, just unhook your old one, plug it in to the new one and see if it operates without the engine running(key to run positon but not running)

blainemaxwell

I just swapped TB with the one on my truck and the one from the boat works on the truck. I did the same thing with the TAC module and it worked also. I must have a wiring or tuning problem, but what?

blainemaxwell

Wooohoooo!!!! I figured it out after all the BS extra wires I thought I needed, busta9876 was wright on. The APP only uses about the middle half of its travel to open the throttle blade to WOT. And I had my pedal set up to use all the travel. I played with shimming the pedal at rest ( clearing the codes every key cycle) until the PCM liked the value at rest and wallah it worked, but if I go full throttle the TB closes and the codes return. All I have to do now is make a stop at full throttle ( at the TB) before APP full throttle.

BTW I did not need any extra wires mentioned above.
As far as the other APP that I tried not working, I had not cleared the codes with my scanner before trying it

Thanks for all the help guys.