Why is my truck freaking out?

Asked by Apr 25, 2014 at 11:37 PM about the 1991 Chevrolet C/K 1500 Silverado Extended Cab SB

Question type: Maintenance & Repair

It was doing fine when I noticed that my speedometer began jumping up and down, the brake light came on, the transmission is shifting in and out of overdrive, and it hesitates.  It's definitely and electrical issue, I just have no idea what's going on.  Can anyone help?

15 Answers


A 91 should have a 700r4. The torque converter clutch is activated electronically. Are u sure its shifting out of overdrive or are you feeling the TCC engage and let go. Im saying this because of 2 things. A 700r4 is hydrolic and shifts on its own and the tcc will only engage over a certian speed and lets go when the brake is applied. It sounds like the computer is freaking out ir you have a bad connection somewhere.

I drove it today Andrew and you're right, I am feeling the TCC engage and let go. I'm certain it is connected to the other things going on as it happened all at once. I am hoping it's not the computer freaking out. I will check the connections. I just put a steering column into it about three weeks ago. Could it be perhaps the neutral safety switch?


Make sure the ignition switch got plugged back in securely. Is the switch on the column you old one or the one from the column? It could cause this

I installed a new ignition switch when I installed the column. I decided the difficult location warranted a new switch so I wouldn't have to replace it later. I checked it after reading your answer and it is plugged in securely. I really hope you have other ideas as I am stumped over this.


it says your brake light came on? your brake warning light? abs? or actual brake lights?

The brake warning light.

Hey Andrew, do you know how to enable the on board diagnostics? I don't have any fancy machines to help me diagnose this problem. By the way, I am grateful for all your advice.


On the connector jump the 2 pins on the top right together. Turn the key to "on" and it will begin flashing long flashes are 10 and quick flashes are 1. First and last codes are always 12. If it doesnt show code 12 then there is an ecm problem


Andrew has given you info on getting your onboard diagnostics codes, something went awry with that steering column job - either that - or you need to call a priest for an exorcism. Personally I'd stick with letting Andrew assist.

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Sounds like sound advice Chassy, I'm going to take you up on that. I'm going to do exactly as you say Andrew. I'm pretty sure I can handle it. We have storms coming and they are pretty close so I will do it tomorrow and keep you up to date on my progress. Hey Chassy, do you know anyone who can perform an exorcism? Just in case.


no advice on exorcisms -sorry.

1 out of 1 people think this is helpful.

Hey Andrew. Sorry it took so long to get back to you. My house was destroyed by a tornado that tore through here a week ago. You prob ably heard about about them. Now that the rubble has been cleared and the rebuilding has begun, I can get back to my truck repair. I checked all of the connections on the steering column and they all appear to be plugged in fully. I then jumped out the connector and got one short flash followed by two more short flashes. This pattern repeated itself over and over. That's all I got. You think maybe the ECM is bad?

I just crawled out from under my truck after discovering that the connector that plugs into the speed sensor was completely destroyed. On wire was torn loose and the other wire is hanging on by a thread. I'm going to change out the connector and see what happens. I'll be in touch.


That plug will have alot to do with this. And yes i have heard alot about those storms coming thru. Glad your ok. The TCC will only engage after a certain speed (usually around 45mph). If it was getting an intermittent signal it would cause this. Needs fixed anyway. Not sure if this would cause the brake light.

Hey Andrew. The problem is solved. It was the disconnected Speed Sensor. You should have seen the plug, it was absolutely destroyed. After splicing the new plug to the wires coming from the truck (of course I used heat shrink type butt splices) the truck is doing fine. Like you, I'm not sure what the brake warning light had to do with all this, but it's operating normally as well. I cannot thank you enough for all your help. I'm not sure I would have solved this without you. Take care, and I hope we get the chance to talk again soon.

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