Transmission won't engage plus several electrical problems, rodents caused short under fuse box

G

Gman's friendly neighbor

New member
May 11, 2025
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Dunlap TN
Hello, glad to have found this forum. I'm a retired shop owner and Japanese car mechanic from the 90's and early 2000's. As a favor I told my neighbor I'd fix his 2005 Sierra 2500 after it was in a local diesel shop for a month with no results. Problem evolved from a symptom that seems pretty common for these vehicles. Truck is mint for an 05, 125k miles and perfectly maintained, from California so no rust at all. He said about 2 months ago one morning trans didn't engage, he turned off engine, restarted and it went into gear fine. Drove for a week and problem reoccurred, slowly taking more on and off cycles to engage over the coming week. Then pulling up the mountain engine performance tanked, running on 4 it seemed. He pulled over and saw smoke coming from under the main under hood fuse box behind drivers side battery right by ECU. Towed to shop, tech said it was loosing power to 4 injectors intermittingly and took numerous attempts to get trans to engage but continuously popped out of gear "taking 10 minutes to move out of shop" Apparently he repaired 2 wires that had melted under fuse box (was full of nuts and droppings) a green and a brown/white. The rest of the wires seem unaffected. I checked the ecu and pcm connections, perfect. Codes are 102, 202, 203, 205, 208, 700, 2149, 841, 871, 872. And to clarify the trans does actually engage, audible sound and slight grab at both R and D, but very very slight pull when accelerated, like massive slip so obviously i didn't retry to drive. Blinking light under R position but not D

Said I needed to create this account to access wiring diagrams so I thought I might as well post just in case anyone has any ideas. I have no access to information besides what can be googled. Very grateful for and help of links to applicable wiring diagrams



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2004LB7

2004LB7

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Dec 15, 2010
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Welcome

Let us know which wiring diagram you need and I'll post it up. There are hundreds of diagrams so you'll need to let us know what circuit or item you are repairing. "Fuse box" is a difficult one as it's spread across many pages. So individual circuits help us narrow it down
 
G

Gman's friendly neighbor

New member
May 11, 2025
4
1
3
Dunlap TN
2004LB7 said:
Welcome

Let us know which wiring diagram you need and I'll post it up. There are hundreds of diagrams so you'll need to let us know what circuit or item you are repairing. "Fuse box" is a difficult one as it's spread across many pages. So individual circuits help us narrow
Click to expand...
the trans computer, trans, and the ficm (what I know as an ecu) diagrams would be great. I’m pretty confident the burned wires and other effected wires go to one and both of the control units. The trans computer in the fan shroud and what I’ve assumed is the ficm tucked below the drivers side battery. I read the 5 speed (04-05) rarely have tcm failure. With all those codes and wire meltdown under the fuse box I guess I’d start at the basics and ensure power supplies at the ecu’s and that outputs are reaching the trans. Also any factory flow charts for any of those those trans codes would be great. Since it won’t pull I guess I have to start there. The short was moderate and melted a good bit of insulation, must have popped a fuse or something somewhere, hopefully the control units would be protected in such an event.
 
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2004LB7

2004LB7

Super Moderator
Staff member
Dec 15, 2010
8,554
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113
Norcal
Gman's friendly neighbor said:
the trans computer, trans, and the ficm (what I know as an ecu) diagrams would be great. I’m pretty confident the burned wires and other effected wires go to one and both of the control units. The trans computer in the fan shroud and what I’ve assumed is the ficm tucked below the drivers side battery. I read the 5 speed (04-05) rarely have tcm failure. With all those codes and wire meltdown under the fuse box I guess I’d start at the basics and ensure power supplies at the ecu’s and that outputs are reaching the trans. Also any factory flow charts for any of those those trans codes would be great. Since it won’t pull I guess I have to start there. The short was moderate and melted a good bit of insulation, must have popped a fuse or something somewhere, hopefully the control units would be protected in such an event.
Click to expand...
The ECM is down by the driver's side battery. TCM on the fan shroud divers side. FICM up by the alternator passenger side
 
G

Gman's friendly neighbor

New member
May 11, 2025
4
1
3
Dunlap TN
Awesome replies, this is a pro forum and an excellent resource. Follow up to what fixed it, there were 3 problems. The burned wires were for the headlights not computer related. When checking fuses I noticed low battery voltage (12.2) with key on but full 12.6 at the battery. This led me to change the ignition switch which immediately fixed the transmission problems. Then able to drive it I experienced it running poor with 2 codes 202 and 2149. That led to repairing the #2 injector connection, he's real picky so we bought a new connector recommended by another post.
The biggest surprise was that the local diesel shop got so confused by these seemingly common flaws for this vehicle, it happens sometimes I guess but he referred to himself as a "B+" diagnostic man. Laughable. Dunlap TN is hard up for a full service diesel shop if anybody's looking to relocate. Thanks again and big hats off to all the guys on the front lines solving these problems everyday, it's a tough job, much respect
 
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