2006 Chevrolet Silverado P0758

Tiny
DERDY9
  • MEMBER
  • 2006 CHEVROLET SILVERADO
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
Short version: I temporarily tapped my aftermarket radio power wire to the CRUISE fuse bc the harness adapter was bad. I didnt get around to fixing it. The radio shorted, blew the fuse, and the P0758 came up. I checked all wiring and replaced fuses. The truck only drives in third gear unless I shift manually. Is this simply a bad ignition switch that was caused by the short?
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Sunday, November 23rd, 2014 AT 8:05 PM

5 Replies

Tiny
CARADIODOC
  • EXPERT
How were you able to remove the original radio? GM cleverly designed the Body Computer into it so it has to stay in the truck. Have you tried reinstalling it to see if the problems go away?
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Sunday, November 23rd, 2014 AT 8:22 PM
Tiny
DERDY9
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I installed the aftermarket radio several months back. The radio isn't the problematic issue. I've driven it for several months with no issues. It started when a wire came loose from the butt connector and shorted. I reinstalled all the wiring and the radio is fine and fuses are good. But the truck only drives in third gear unless I manually shift. Its only the single code P0758. I'm lead to believe that somehow, the ignition switch went bad in the process.
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Sunday, November 23rd, 2014 AT 8:32 PM
Tiny
CARADIODOC
  • EXPERT
You aren't going to damage the ignition switch. The circuit was protected by the fuse. You would have to draw excessive current for quite a while to overheat the switch contacts and connector terminals, then numerous things on that circuit would be dead.

It's more likely you have a problem with shift solenoid. And if you have to pull the radio again for anything, get rid of those butt connectors. The only thing worse for this environment is snap-together Scotch-Lok connectors. The wires should be slid together so the strands slide into each other, solder the splices, make sure there's no sharp points sticking up, then seal them with heat-shrink tubing. Don't use electrical tape anywhere on your truck because that will unravel into a gooey mess on a hot day.
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Sunday, November 23rd, 2014 AT 8:44 PM
Tiny
DERDY9
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"Worse for the environment"? I didn't know the butt connectors contributed to my exhaust fumes. And electrical tape is fine if taped up right. I live in Texas. I know about heat. Why would it be the shift solenoid compared to the ignition switch? This problem occurred simultaneously with the fuses blowing.
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Sunday, November 23rd, 2014 AT 8:52 PM
Tiny
CARADIODOC
  • EXPERT
The "environment" means the humidity, heat, and vibration in the environment the electronics live in. Cars and trucks are the worst possible place to stick computers, connectors, and splices, yet the insane engineers can't seem to be satisfied with how overly-complicated they've made our vehicles.

I live in Wisconsin and I know all about electrical tape in cars. I don't know what you consider "taping it up right", but you won't find electrical tape on a vehicle coming from the manufacturer. You may know more than the engineers though.

Besides being a mechanic specializing in electrical repair, I've been a tv repairman since the '70s, and I can guarantee you professionals in both fields would never even consider using mechanical fasteners for electrical work. Scotch-Lok and butt connectors are by far the number one cause of trailer light problems due to the corroded wires they cause. My friend just moved his sister and brother-in-law up here from Austin. They both work for 3M and will tell you their Scotch-Lok connectors were never meant for use outside of a vehicle. I don't use them inside either. My point is not to argue the lack of professionalism in using these shortcuts, (you already found out why); it's simply to help you avoid future problems. What would you think of me if I didn't care enough to share that advice?

As for the fault code, they never say to replace parts or that one is bad. They only indicate the circuit or system that needs further diagnosis, or the unacceptable operating condition. Thanks to the proliferation of computers, it is no longer possible to draw conclusions like we used to do. In the past we would say since the problem started right after a fuse blew, it must be related to that fuse. I haven't looked at a diagram to prove me wrong, but generally there is no fuse dedicated for just the cruise control. Typically a fuse will have a number of items listed in the owner's manual that it's for, but most fuses protect multiple items, and not all of them will be listed because owners wouldn't recognize or understand half of the terms. On most cars and trucks the cruise control system is just an extension of the Engine Computer, and there will be multiple fuses for that.

You may have other things that aren't working that you don't even know about. Manufacturers often combine things to include an item you will notice. A common example is to combine the radio's memory circuit with the horn. With a blown fuse you'll notice the inoperative radio, but not the horn until you need it. While your fuse might be labelled "cruise control", there could be some other circuit tied in with it that has the problem.

There's no cruise control wires behind the radio, and I'm pretty sure you didn't remove the steering wheel to connect the radio, so I'm guessing the wire you touched was at the inside fuse box. There's another one under the hood.

I can envision three possibilities for this fault code. One is there's another blown fuse that you haven't found yet. The second is the fuse blew because of a shorted driver circuit in the computer caused by shorting the radio wire. The third is a connector worked loose while you were working in the area, and the wire for one of the shift solenoids is open. The computer problem would be WAY down near the bottom of my list and I'd be surprised if that's what it turned out to be. Most computers have a lot of safeguards built in for just such things, and it's usually pretty hard to damage them. My first choice is the overlooked fuse. Remember, I'm an experienced professional in two fields, and I can't tell you how many times my coworkers and I have gone down the wrong path or wasted time looking for a non-existent problem after overlooking something simple. Every week we get a good chuckle at someone's expense, but it reminds us how often this happens.

To get back to your ignition switch, there's typically only three, and sometimes four major switches built into it. That means those few circuits have to power everything that turns on with it, and there is not going to be a set of contacts just for the cruise control or just for the transmission. The most common part to fail used to be the section that turned on the heater fan and power windows, especially for people who used the fan on the higher settings a lot, but today most of those things are run by computers, and they do all the heavy switching. Still, if the switch had a set of arced contacts or overheated terminals in the connector, there would be multiple things that don't work.

I would pursue the fault code at the dealership or a transmission specialty shop. The dealer will have an entire book just for diagnosing transmission codes. If they're like the dealer I used to work for, the service adviser will photocopy the relevant pages if he isn't busy with customers. At the transmission shops, very often they can tell you exactly what you're likely to find for a code on a certain model. Most of the time whatever you can present, they've seen it before.
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Sunday, November 23rd, 2014 AT 11:44 PM

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