Headlight / Engine power reduced...PLEASE HELP!!

M

Murse

Member
So i'm having this problem where if my headlights are on, and I either use a blinker or turn on high beams I will get "engine power reduced" and throttle will be dead. Restart the car and everything works until one of those things happen again.
If I turn the headlights off, I can do everything fine, blinkers, high beams. I have unplugging one headlight, same problem. Both headlights and instantly engine power reduced without doing anything (assuming this is safety in case you dont have headlights).
Code that pops up is x7E8: P2138 - Throttle/Pedal Position Sensor/Switch D/E Voltage Correlation (SES, Pending, Current, Old, History)......which only makes things more confusing.
When this all started I assumed TPS/PPS was the problem, new pedal, new throttle body.
I am using those larger LED headlights that multiple here are using, they all seem to be functioning fine. I'm lost at this point....
Only other thing I have noticed is that with the lights on....left turn signal nothing changes....right turn signal the engine RPM increases very slightly with the turn signal....Any thoughts to at least help me move in the right direction would be amazing.

Thanks!!
 
G

Gtstorey

Goblin Guru
Sounds like you have headlight power wired into something that doesn't need it. Or you are pulling power for the headlights from some part of the throttle/pedal sensor circuit. You need to follow the factory diagnostics for the P2138 code and see if that doesn't lead you somewhere. Beyond that is visually tracing each of the headlight wires and the throttle/pedal wires to look for the issue.

Does hi vs low beam make a difference? I think I remember the low beams are fed directly from the switch to the relay and the hi beams are switch to bcm to a relay, at least on the later models. You need to add your signature with donor information because the wiring has differences between the different donors.
 
G

Gtstorey

Goblin Guru
And there is a slight chance this is a ground issue where voltage finds a path to ground by back feeding through a sensor because it can't make it to ground through the correct path.
 
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M

Murse

Member
thanks! Do you think this could be a bad headlight relay? Are both low beam and high beam supposed to be on together? I do notice that low beams do not shut off when high beams are on. I thought about replacing the front fuse panel as it looks like those relays cannot be replaced.
2009 cobalt ss/tc
 
M

Murse

Member
Gtstorey said:
And there is a slight chance this is a ground issue where voltage finds a path to ground by back feeding through a sensor because it can make it to ground through the correct path.
Click to expand...
sorry should have replied here, but post a new reply to main post.
 
Rttoys

Rttoys

Goblin Guru
Since I’m on my phone I can’t see if your car is listed in your signature and it looks like these are your first posts, so a few questions:

what year was your doner vehicle?
Is this something new that just happened?
Is your car complete or where are you in your build?
 
M

Murse

Member
I purchased the kit from the original builder with basically no miles on it. 2009 cobalt 2.0l turbo. I originally thought this was a new problem, but I think on normal daylight hours the lights just would come on. Car is complete and running, so unfortunately I cannot see any splicing or wiring as he has it very well taped and harnessed up.
 
G

Gtstorey

Goblin Guru
Turn you
Rttoys said:
Since I’m on my phone I can’t see if your car is listed in your signature and it looks like these are your first posts, so a few questions:

what year was your doner vehicle?
Is this something new that just happened?
Is your car complete or where are you in your build?
Click to expand...
Turn your phone sideways and it will usually show the signature.

The P2138 will cause reduced power so that is still the starting point. Bad headlight relay won't cause the problem. Maybe not impossible a bad battery and the additional headlight load is causing voltage issues. But that is way down the list of possibles.
 
Joebob

Joebob

Goblin Guru
At the very bottom of my post long ago with similar issues:


Short answer was it was not the throttle pedal nor the TB but the connector loose pins or the wires that you have to splice longer. replacing the connectors and wiring, fixed the issue.

As discussed in other email chains of not starting due to turn signal stalk not plugged in, Check is there are issues there or replace turn signal stalk. You could have an internal short there backfeeding grounds and such.



Joe
 
M

Murse

Member
Could someone post a wiring diagram for the goblin? I am wondering what splicing is/was required and maybe that might help me narrow things down, I looked a bit and couldn't find a wiring diagram as to what changes you make with the goblin.
 
G

Gtstorey

Goblin Guru
There isn't a single finished wiring diagram for a Goblin. There are pieces scattered on the forums, but not anything complete. And the pieces can vary depending on donor. You have to take a wiring diagram for your original donor and figure it out. For the most part each piece that remains won't change the diagram that much, although a few intermittent connectors may be removed. But the start and stop are in the same locations and usually with the same wire colors. The biggest change is probably the data wires.
 
Ross

Ross

Goblin Guru
Not really a wiring diagram, but it is a start:
Main wiring harness map for DF Goblin with lengths. Need to blow up the picture a lot to see the lengths.
Manual for your goblin donor. Downloadable 7-zip or WinRaR
 
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