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Discussion Starter · #1 ·
Hey Everyone. Really weird issue with my 1994 K1500 6.5 TD. When I hit my brake pedal, the Speedo jumps and the trucks stutters and surges…in drive or park. Actually even stalled while in park when I mashed down on the pedal hard enough. Any idea what might be causing this?
 

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I would start by going through all of your grounds. remove each one, clean then reinstall
Have you checked for any codes?
 

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Discussion Starter · #3 ·
I would start by going through all of your grounds. remove each one, clean then reinstall
Have you checked for any codes?
That's a good idea. No...I haven't checked for codes. Because I don't have a reader for OBD-1 i keep forgetting it's an option... LOL
 

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Discussion Starter · #5 ·
You can check for codes using a paperclip and this info: Diagnostic codes OBD I
So as a follow up...I have a trailer brake controller in the cab. When I slide the switch that would manually engage the trailer brakes, it does the same thing...not quite as bad as pressing the pedal, but it does stumble and the speedo needle jumps up.
 

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Remove the STOP/HAZ fuse and see if anything changes.
Do the same with the BRAKE fuse.
 

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Discussion Starter · #7 ·

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Discussion Starter · #8 · (Edited)
It does not do it with the STOP fuse removed! What does that mean? BTW...how did you think to check that?!

With the STOP fuse in and the BRAKE fuse out...the truck still stumbles and stalls with the brake applied.

I didn't think anything of it...but I had to refill my coolant reservoir and the hose overflowed/flowed directly behind the tank for a bit before i caught it....could water have gotten into anything in that area to cause this?
 

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Discussion Starter · #9 ·
Remove the STOP/HAZ fuse and see if anything changes.
Do the same with the BRAKE fuse.
It does not do it with the STOP fuse removed! What does that mean? BTW...how did you think to check that?!

With the STOP fuse in and the BRAKE fuse out...the truck still stumbles and stalls with the brake applied.

I didn't think anything of it...but I had to refill my coolant reservoir and the hose overflowed/flowed directly behind the tank for a bit before i caught it....could water have gotten into anything in that area to cause this?
 

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Doubt you caused any problems with the coolant.
There should be a relay above the master cyl. on the fire wall, to the drivers side of the BARO sensor.
That is the brake lamp/CHMSL relay only on 94's. Unplug that and see what happens.
 

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Discussion Starter · #11 ·
Doubt you caused any problems with the coolant.
There should be a relay above the master cyl. on the fire wall, to the drivers side of the BARO sensor.
That is the brake lamp/CHMSL relay only on 94's. Unplug that and see what happens.
I unplugged it...a gray relay mounted on the firewall...truck would not stumble with that unplugged. Does that mean that relay is bad?
 

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There is a short in the brake/turn lamps. CHMSL lamp has been cleared by removing the relay.
Could be wires, or bulbs, or corrosion or even the relay or multifunction switch.
The PCM always has 2 brake signals going to it, one OFF, one ON.
When you press the brakes those signals reverse.

643735
 
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Discussion Starter · #13 ·
There is a short in the brake/turn lamps. CHMSL lamp has been cleared by removing the relay.
Could be wires, or bulbs, or corrosion or even the relay or multifunction switch.
The PCM always has 2 brake signals going to it, one OFF, one ON.
When you press the brakes those signals reverse.

View attachment 643735
Wow. This will be exciting LOL. Best place to start? I’m terrible with electrical. Thank you so much for your help. I’m impressed you dialed in on this so quickly!
 

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Discussion Starter · #15 ·
Trailer plug shorted
That's an interesting thought...I did tow a trailer recently. My plug is mounted on the side of the bed unfortunately making it a bit more difficult to get to but worth checking!
 

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^^ X2 on what DP said. Short in the plug, or trailer brake wiring/controller Can cause your problems.
 
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Discussion Starter · #17 ·
^^ X2 on what DP said. Short in the plug, or trailer brake wiring/controller Can cause your problems.
I will tear that apart tomorrow first. (y) Thank you all for the advice!
 
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