Urgent help needed. 2013 GMC 2500HD, broken down in Brazil

[Martyn]

Posting for a good friend of mine who has broken down in Brazil. He is trying to get the truck onto a boat back to the US but it has broken down. we are looking for some sound ideas or suggestions on troubleshooting this issue so he can make the boat.

This is the message he sent to me:
”Writing from Brazil with a frustrating issue, I hope you can help. Please note that parts are relatively unavailable. Although we do have a full set of tools and a fuel pump, alternator, water pump and starter on board.
Vehicle- 2013 GMC 2500HD, 6.0 gasoline, 4x4, 108,000 miles, carrying a Northstar camper for the past 20,000 miles from USA to Brazil.
Issue- Cranks but no start, no spark. Eventually started and idled rough. Then ran fine. Another day it started and ran fine then went into low-power and stalled/died. Another day it ran fine for hundreds of miles and multiple starts. Now back to crank but no start, no spark. Urgently need it to start to put it on a boat back to the USA.
Findings and attempts- Fuel pump noise is heard. Fuel is at rails. Fuel pressure was tested and in range. Batteries (2) are at full charge and full output. Pulled and tested all fuses. Pulled, cleaned and tested continuity on all grounds. Checked and cleaned TPS connection. Pulled, cleaned and reconnected ignition switch. Used other ignition key. Exchanged relay from AC compressor/fuel pump. Cleaned air filter. Cleaned MAF. Cleaned throttle body. Disconnected and reconnected batteries, waited 30 minutes. Dash lights up, CEL comes on. Stabilitrak light comes on. Clockspring was recently replaced. Checked for codes.......
Codes- P0122, P0686, P0685, P1682”.

I checked the codes and got this:

P0122 throttle position sensor

P0122 GMC Possible Causes
What does this mean?
Faulty throttle position sensor
Throttle position sensor harness is open or shorted
Throttle position sensor circuit poor electrical connection


P0686 Engine Control Module Power Relay Control Circuit Low
P0686 Possible Causes
What does this mean?
Weak battery
Low voltage while cranking
Faulty Engine Control Module (ECM) power relay
ECM power relay harness is open or shorted
ECM power relay circuit poor electrical connection
Blown ECM fuse
Faulty ECM

P0685 GMC - Engine Control Module Power Relay Control Circuit Open

P1682 GMC Possible Causes
What does this mean?
Faulty ignition switch
Ignition Switch harness is open or shorted
Ignition Switch circuit poor electrical connection
Faulty Engine Control Module (ECM)

There is a technical note for GMC on the last code see link here

P1682 GMC: Code Meaning, Causes, Symptoms, & Tech Notes (With Video)

There are 2 ignition 1 voltage circuits supplied to the Engine Control Module (ECM). The first ignition circuit is provided by the powertrain relay,

www.engine-codes.com

 

[alanymarce]

Sounds as if there's a gremlin in the electrics (I know, stating the obvious). We had similar weird problems in East Africa on one trip until we found an auto-electrician who really was an expert - all sorted in a couple of hours. I suggest finding a good auto-electrician in Brazil.

So, where in Brazil? It's almost as big as Europe and bigger than the 48 contiguous states of the USA. I could ask some contacts however there's no point asking someone in Porto Alegre if the vehicle's in Boa Vista...

 

[Herbie]

The ECM Relay and power codes make me think that's your main issue. The ECM drives the spark and if there's an issue w/ voltage or current supply, it's a likely failure point.

One thing to check is that GM often used the same size relays in multiple positions - if your friend does not have spare relays (or replacements are not available), try swapping positions of like-sized relays to see if the problem moves or resolves sufficiently for his transport issue. (On my Chevy van, for example, the fuel pump, A/C, and I believe ignition relays are all the same p/n.)

The other obvious one to check in these situations is the ground locations. GM likes to "pool" ground connections to several nodes around the chassis. These are theoretically all at the same electrical potential, but corrosion or a bum connection at any one of these can cause a host of oddball behaviors. Chase down all available ground paths and give 'em a tug and, if necessary, a wire-brushing, to ensure everything is clean and secure.

 

[alanymarce]

...and while I think of it, you can by-pass some relays, at least temporarily. To echo Herbie's comments, on our problem in Africa, one of the things the expert did was to clean up all of the ground connections, as well as most of the others - dust and corrosion are the enemies of electricity...

 

[roving1]

So, where in Brazil? It's almost as big as Europe and bigger than the 48 contiguous states of the USA. I could ask some contacts however there's no point asking someone in Porto Alegre if the vehicle's in Boa Vista...

This. I may have a contact in Sao Bernado do Campo outside Sao Paulo that could maybe help.

 

[quickfarms]

Grounds are often overlooked but are a necessary item.

Personally I tend to add grounds if I have electrical gremlins.

I do hate ECU’s

It is so much easier to deal with the old mechanical stuff

 

[dirtnadvil]

My GM has always had weird electrical problems, Most always a bad ground. Its a good place to start as you can clean them up your self and see if it helps....Also mice can chew up wiring. Anyways, good luck to your friend...

 

[Martyn]

My friend Mike is waiting for a mechanic with a scanner that can work with his GMC. He has started work on cleaning all the grounds, and he is testing the voltage in and out of the relays. We are currently focusing on the electronic part of the ignition switch, we are working on getting the wiring diagram of the switch itself, if you have one for this year of 2500HD please share.

Mike is thankful for all the help he is getting, it’s very isolating to breakdown in a foreign country and the feeling that others are out there willing to help you can make all the difference. Keep the suggestions coming and I’ll keep you posted on how we are doing.

 

[jeep364]

Consider posting on Gm-trucks.com , huge group over there.

Hope he gets it sorted.

 

[NevadaLover]

Here is the diagram you need.

 

[Martyn]

Thank you for all of your assistance so far. I’m passing it all on to Mike. I know that having this help from afar is definitely lifting his spirits.

 

[alanymarce]

So, where's the vehicle?

 

[jadmt]

So, where's the vehicle?

must be a secret...seems like a reasonable question.

 

[Martyn]

must be a secret...seems like a reasonable question.

I’ll ask Mike and let you know where the vehicle is.

 

[Martyn]

Here is the news from Mike.
We are located in ”Dois Irmaos. Near Novo Hamburgo. We got it started today. Not the switch. We had to jump power from fuse 12 to fuse 5 which is for the THROTTLE POSITION SENSOR. Ran reallly rough. It did idle. We also now have a code U0100 (Code U0100 stands for Lost Communication with ECM/PCM).

But it starts. I have been on with an engineer for the last two days. He has been telling me which fuses to jump and check. Tomorrow I will take the fuse plate out and check the wiring. They think we have a ground issue. Can’t wait.

The electrical diagram you sent was really helpful.”