LS Swap Troubleshooting..no pedal response

[shearjs]

We're just about to wrap up our 70 GMC with an LS swap, and have been doing some trouble shooting by just driving some shake down miles. It's been driven around 40-50 miles with no issues, and then this started. When the truck gets up to operating temps, it starts to develop a slight miss, and then the accelerator pedal stops functioning. The computer shows codes for the pedal sensor and for the throttle position sensor. We tried replacing the throttle body, and the pedal sensor, with no improvement. I'm kinda stumped at this point and open to ideas. The engine is a LQ4 6.0L from a 2004 Silverado 2500. It has a reworked stock harness and a basic computer tune eliminating VATS, emissions, etc. Any help would be greatly appreciated. Thanks.

[VroomVroom68]

Oh no, did you get a drive by wire one? I was going to say it's the throttle cable, but I'm stumped.

[BR3W CITY]

which codes exactly?

Does all of your stuff match (year/pedal/tac/tb/ecm).

[shearjs]

There were 3 codes: P1125, P1516, U0107. All components are from the same vehicle.

[smoky02]

My truck does that on occasion. I clear the codes and it works great. I have tracked down what component is intermittent though

[stingray72]

My pedal stops working if I stomp the pedal hard. Truck keeps running just no pedal. I have to turn the truck off and wait for a couple minutes then crank it back up and go again. it's baffling

[BR3W CITY]

Sounds like the pedal is having an issue with its position sensor readings. If you put a meter on the signal wires on the pedal sensor(s) you can check for an abnormal voltage sweep. Iirc the normal sweep is 0-10v or 10-0v. Newer stuff has 2 position sensors that should read equally opposite, in order to double check each other....if that makes any sense. Search for TAC pedal voltage on ls1tech for a little more clear info. I'm on my phone and going off memory.

[shearjs]

Thanks for the suggestion. I'll check it out over on LS1tech and see if I can dig up any info. I appreciate the help.

[jorgensensc]

This is similar to the problem I have. Sometimes if I go WOT at about 70 the engine goes into this limp mode, no pedal response. We narrowed it down to an issue with my ECM though, because I get code p0606, PCM internal performance problem.

[stingray72]

Originally Posted by jorgensensc

This is similar to the problem I have. Sometimes if I go WOT at about 70 the engine goes into this limp mode, no pedal response. We narrowed it down to an issue with my ECM though, because I get code p0606, PCM internal performance problem.

I bought a bluetooth ODB2 adapter and the torque app so I'm going to piss off the neighbors this weekend and see if I can get the pedal to go limp in the neighborhood while reading codes to figure out what's going on.

The minute I do it away from the house on purpose truck probably won't come back to life for me. lol

[shearjs]

We grabbed a replacement wiring harness from the pedal sensor to the TAC module yesterday, and it's temporarily working so far. I'll keep this thread updated as we progress. I appreciate all the responses.

[stingray72]

Originally Posted by jorgensensc

This is similar to the problem I have. Sometimes if I go WOT at about 70 the engine goes into this limp mode, no pedal response. We narrowed it down to an issue with my ECM though, because I get code p0606, PCM internal performance problem.

I've got the p0606 also, looks like it's time to find a tuner and or new PCM from my research so far

[BR3W CITY]

So apparently I found that the p0606 code can also be triggered by a b.s. 5v input reference on one of the busses. The o.p. sensor or a 5v gauge reference can cause this (on the newer stuff obviously).

Is there a VIN mismatch in your tune? That can also cause random dbw and bus errors.

[shearjs]

The wire swap did not fix my issues so I'm back to square one. The re shouldn't be any vin mismatches within my PCM but anything is possible I guess. The truck is now having this issue regardless of engine coolant temps so that shouldn't be related. I'm open to any ideas. Thanks.

[BR3W CITY]

Tac module itself could be failed/grounded out. When its already at operating temp, does it idle normally (if your not driving, just sitting there)?

If there is a large enough misfire, or you rapidly decelerate, the load change to the engine can bog it out, trigger a "low engine power" code, and limp the truck. On a dbw setup that means killing the pedal input. Can it maintain an idle on its own?

When you mentioned the temp, I thought it possible that when the truck came off of cold-start, the idle was dropping too low to maintain, triggering either a miss or low power fault and killing the pedal.

For ****s, I disconnected the tac and pedal from each other, pulled the battery for 20 minutes. Re-connected them while it was off, put the battery back on, started the truck and let it do a full idle-warmup. The fault never came back after that.

[shearjs]

It idles normally, but once you put it in gear and take off, you lose the pedal then the engine starts to miss. It doesn't completely die, but runs pretty rough at that point.

[BR3W CITY]

Humor me;

Idle it warm, foot on brake. Put into gear, but leave foot on brake. Does the simple act of putting increased load on the engine seem to trigger the event? Something like putting the truck in gear and let it try to idle up a driveway egress.
If it changes based on load we have a direction to look.

[jorgensensc]

Originally Posted by BR3W CITY

So apparently I found that the p0606 code can also be triggered by a b.s. 5v input reference on one of the busses. The o.p. sensor or a 5v gauge reference can cause this (on the newer stuff obviously).

Is there a VIN mismatch in your tune? That can also cause random dbw and bus errors.

Ok, I'm not trying to hijack the thread, but I may tag along for good measure.
Br3w City, what exactly do you mean? What type of erroneous 5v reference could cause this? I'm using the original oil pressure, coolant temp, and tranny temp switches via can bus for my gauges. I thought that for some reason the can bus gauges might be affecting the computer before I took the suburban to the dyno ( often when I would plug them in to the DLC the engine would idle up and smooth out.) but I didn't understand how that could affect the computer since the gauges only read what's on the canbus. After the dyno tune I didn't hook the gauges up when testing it, that is when I got the P0606 code, so I thought the gauges had nothing to do with it. But now I wonder, because I used a pull up resistor (recommended by Speedhut) on my speedo and tach, which are not run via canbus (didn't have them in the right size yet in canbus), but do get their signal from the ECM. Could that be the issue?
Shawn

[BR3W CITY]

Originally Posted by jorgensensc

Ok, I'm not trying to hijack the thread, but I may tag along for good measure.
Br3w City, what exactly do you mean? What type of erroneous 5v reference could cause this? I'm using the original oil pressure, coolant temp, and tranny temp switches via can bus for my gauges. I thought that for some reason the can bus gauges might be affecting the computer before I took the suburban to the dyno ( often when I would plug them in to the DLC the engine would idle up and smooth out.) but I didn't understand how that could affect the computer since the gauges only read what's on the canbus. After the dyno tune I didn't hook the gauges up when testing it, that is when I got the P0606 code, so I thought the gauges had nothing to do with it. But now I wonder, because I used a pull up resistor (recommended by Speedhut) on my speedo and tach, which are not run via canbus (didn't have them in the right size yet in canbus), but do get their signal from the ECM. Could that be the issue?
Shawn

When I posted it I thought of your build. What I read is that a damaged/fault/shorted oil pressure sensor is the common culprit for p0606 errors in the canbus equipped trucks. .5v = 0psi 4.5v = 130psi
If there is a failure on this circuit, it prevents vvt operation, it uses it for cam phasing. If there is ground-noise, the latent voltage on the ground side can cause a b.s. input on that particular loop. Thats why so many of the canbus wires say "low reference 5v" instead of "ground", they don't want a shared ground like an engine block or grounding post.
It can also mean that there is a general supplied current on the canbus system ABOVE 5.23 volts, which is the max that the 5v system can handle without triggering the code.

My eyes are falling asleep out from under me, but I'll try and find the threads I was looking through yesterday. None had a clear cut explanation, but I'm piecing together about 20 threads worth of stuff to deduct something. Aren't canbus gauges daisy-chained? So if there is an issue on 1, you can carry it across the rest?

[shearjs]

I tried what you suggested today. Let the truck idle up to running temps. When I put it in gear, the truck idles up, where as it did not use to. Backed it out of the garage fine. Once the accelerator pedal is pushed, I get the miss and lose the pedal. I got a code of NC107 this time around.

[jorgensensc]

That sounds like a vacuum leak. Idles up in gear? Usually they idle down.

[BR3W CITY]

p0107 would be a map, but the NC1o7 code is "NC107 Fault Uknown". I'm pretty sure its not an actual DTC code, I think its basically saying there is a wiring problem. I can't hardly find any information about it. Its come up on MAYBE 3 threads I've seen, period.

Its a default error code of some sort, indicating a wiring problem/short, or internal electrical fault that cannot be diagnosed with a DTC code. Its usually accompanied by another DTC or failure. Guessing a problem with the wiring harness, something internally shorted somewhere, or something stupid like poorly pinned ECM or similar, where your not getting a 100% connection, nor a 100%short.

[shearjs]

It's getting a little frustrating, to say the least. I think what's the most frustrating, is knowing that I drove the truck for 50 miles with no issues, and then this appeared. My dad has a buddy that works for the local dealership. We're going to get him to come by and see if he has any ideas this week. Hopefully we make a little progress. Thanks again for all the help and ideas.

[BR3W CITY]

Ask him to bring his TechII and put it on there. I want to see if there are ecm or tranny codes or another fault code that the regular aldl can't read.


Googling nc107 is useless, as you will only hear about US hwy 107 through North Carolina.

Did you end up replacing the TAC module? or was it just the harness?

Also take a look on the tb for the Purple and yellow wires coming out of the actuator. They pull under their own tension and the pins in the molex plug can work their way out.

[badazmalibu]

I am a Ford tech...as such when I have seen P0606 on Ford products it is generally caused by RF (radio Frequency) interference. The most common cause for this that I have seen is a faulty coil although I have repaired this by replacing the alternator in a few vehicles as well. You could try swapping the coils with another vehicle to eliminate that and just unplug the alternator(power cable included) and drive to see if the problem still exists.
As I said my experience is with Ford products and this may not apply but who knows
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