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Discussion Starter · #1 ·
Hey guys. Left work today and went over some railroad tracks and I noticed my speedo and tach went out. I then noticed my odometer was not working and my batteries were not charging. The truck still drove and I made it home. Got on here immediately. I’m going to start checking loose connections but I figured I’d start this thread hoping one of you guys knows exactly what the problem is. I’m thinking ESS…. Any help would be great. If I figure it out before then I will post. Thanks
 

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Discussion Starter · #13 ·
Because the same non-logical guesses are rampant. Do any of them show the ESS fixing the speedometer?

The logical way to troubleshoot would be to determine what the speedometer and the tach have in common. That requires opening the factory service manual and searching for a common link. More than likely that common link is a ground.
Yes I have an FSM just didn’t have it with me yesterday. I’ll look through it after work. Also the ac compressor doesn’t kick on.
 

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Discussion Starter · #17 ·
Just going to copy/paste myself from a previous post lol. Do you get bulb checks (WTS, WIF, etc?) when you turn the key on?

If the alternator wasn't charging but you get a GEN light on the dash -- alternator bad.
No tach, no charging, but speedo works -- ESS issue.
Tach+charging, no speedo -- VSS issue.
No tach, no charging, no speedo, no bulb checks -- PCM is bad (Maybe not fried, maybe just power/ground issues)
No TACH, No ODO, No CHARGE, No SPEEDO, No AC COMPRESSOR, No WAIT TO START, No GEN LIGHT. I’ll be checking stuff when I get home. Thank you.
 

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Discussion Starter · #18 ·
Tach, charging, and AC compressor will be inoperative if there is no ESS signal. But as others said, that should not affect speedometer or odometer. As said above, look for something in common
No TACH, No ODO, No CHARGE, No SPEEDO, No AC COMPRESSOR, No WAIT TO START, No GEN LIGHT. I’ll be checking stuff when I get home. Thank you.
 

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Discussion Starter · #19 ·
So after looking at some diagrams it appears that the relationship between the ESS and the VSS are circuit K4 sensor ground. I unplugged the ESS and the SPEEDO works and my CHECK BULBS now work. But no CHARGE still which makes sense because the computer doesn’t know the truck is running without the ESS plugged in. I tested the connector at the ESS with the truck on and I get 5 volts between the 5 volt supply and it’s sensor ground which is K4. I’m assuming the ESS is bad and when plugged in is shorting that sensor ground. Any thoughts?
 

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Discussion Starter · #26 ·
That K4 sensor ground is spliced near the fuel filter in the harness and those splices branch out from there. I checked continuity from the engine harness connector where the ESS is located to the PCM and everything was good. Luckily Amazon has the generic ESS for 50$. Part# Standard PC756. I know it’s the cheapo but I figured I’d try it. And it works. Thank you all for your input. I noticed in the FSM in the wiring diagram chapter 8W-30 there is a ton of information at the beginning explaining how the system works and what controls what.
 
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