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BOBBYSS
BOBBYSS, Master Technician
Category: Chevy
Satisfied Customers: 17474
Experience:  ASE MASTER CERTIFIED, AA DEGREE AUTO/DIESEL TECH
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I have a 2004 Chevy Silverado Duramax with a 5 speed allison

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I have a 2004 Chevy Silverado Duramax with a 5 speed allison transmission. last Year I needed to replace the nsbu switch, and everything worked fine until approx 2 weeks ago. I thought the switch was going bad again, but I replaced it and it did not fix the problem. When i put the truck in reverse or drive I can feel it go into limp mode. Often the brake and abs light comes on. The indicator light under the park, reverse, neutral, etc sometimes goes completely blank. If I stop and start the engine often enough, sometimes it will work like it is supposed to, and will continue to work as long as I don't shut the truck off. The next time I start it up, it may or may not work. It is getting worse, and often it malfunctions, going into limp mode or kicking out completely. Today I check the connectors for corrosion going to the tcm, but they look really nice and clean. I tried to check the wiring harness to see if I could find any shorts, etc, but have found none. I feel the problem is electronic, and I am starting to question if I have a faulty tcm. Can you give me any advice?
JA: Is it just the ABS light? Or is the brake system warning light on, too?
Customer: Sometimes both, but most often just the abs light.
JA: Are you fixing your Silverado yourself? What have you tried so far?
Customer: I have been trying myself, but I don't have a scanner to look at the codes, so I plan to meet with a friend tomorrow to see what all codes it is giving. the check engine light is on, so I'm sure it will give some readings. I didn't know if you have had any of these symptoms before to help us trouble shoot the problem.
JA: Anything else you want the mechanic to know before I connect you?
Customer: I think that those are the main things that I think of now.

Hello, my name is***** the check engine light i on then I would scan the computer for codes first. Those codes might help to find the issue. From the description of the issue this is almost always a failing ignition switch. it is common for the ignition switch to fail and cause a loss of voltage to certain circuits and cause this. I would do a voltage drop test of the ignition switch to see if it is failing. It may also be an issue in the rear connector of the transmission if there is transmission fluid getting in it. Please let me know if you need more help.

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Customer: replied 1 month ago.
Just a note to you on the problem I WAS having with the truck. You hit it with the correct diagnosis. The ignitions switch has been changed, and my truck is back to functioning like it is supposed to .
Your answer was very helpful, and I appreciate it! Thanks so much for your time and expertise!

No problem. If you need anything else in the future please let me know. Have a great weekend.