2000 Z71 3rd only, no tach, no speedo.

[Rick Baran]

Hey everyone, I'm Rick Baran. I'm a retired sailor who owns a 2000 Z71. Before anyone comments on my avatar, that's my 1972 Chevrolet Titan 2-axle semi-tractor!

As the title states, my tachometer, speedometer, and odometer have stopped working. My transmission will shift into/out-of Park, Reverse, Neutral, and 3rd. My transfer-case appears to shift normally as well(I have the electric switches on the lower dash to the right of the steering column).

Once in a while(maybe 1 in 25 starts) EVERYTHING will work normally for a few hundred feet up to an entire day's driving(25-30 miles).

Anyways, I have been researching on our interweb, and decided to replace the two Speed-Sensors on the transfer-case. That had no effect whatsoever. I also disconnected the battery and checked ALL fuses with no change.

I read that the VSSB(?) was located behind the glove-compartment. I cannot locate it behind the passenger's glove-compartment. I don't have a wiring-diagram nor do I have a component-location diagram, so I'm having difficulty proceeding any further in troubleshooting.

Do any of you have any ideas as to how I should proceed? I've read several forum-posts discussing the possibility of a bad Ignition-Switch. I've also read about the VSSB, which I take it is a sub-computer and not the big clunky heat-sinked box on my driver-side inner-fender?

I've also considered finding a 6.5 diesel and a 4L80 transmission and replacing my 325k mile 5.7 gas/4L60. Anyone wish to weigh-in on that option?

 

[Rick Baran]

To those of you who at least looked at my posts, thanks for looking. I'll try to get answers elsewhere.

 

[HiHoeSilver]

To those of you who at least looked at my posts, thanks for looking. I'll try to get answers elsewhere.

Sorry that you didn't get any responses. I didn't even see these posts until now. Sometimes they need a bump.

If your cluster works sometimes, even for a minute, I think you probably have a suspect electrical connection somewhere. You could give the harness where it connects a good check. Another common problem that affects the cluster and other electronics is ground problems. Check/clean up the ground from the block to the firewall.

One last note. I know your truck is a 2000. But since it's a Z, it's an OBS body. Your posts would be better seen by the guys who know best in the 1991-99 section.

Maybe we can get a little help moving them so you don't have to retype your life story.

@07Burb

 

[bottomline2000]

You have an OBS style truck so you may have better luck in the 1991-99 section..

That big rig should be a fun retirement project..

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[Rocket Man]

Possibly a bad ground somewhere but that’s all I can think of.

 

[Rick Baran]

Thanks for the responses. Can any of you tell me what sensor actually provides the signal to the tachometer? I was just wondering if that sensor and not the two speed-sensors on the Transfer-Case might've gone bad in addition to a ground.

A few years ago the dash-cover started 'cracking', and is now completely in pieces...kinda llike a Dodge Ram pickup dash. Anyways, that failure allowed my driver's side dash to 'droop' a bit, so maybe the connections are the issue. I'll tear it down today and see what I can find.

 

[east302]

The VSS (near the transfer case) is communicating with the VCM for the speedometer. The screenshots below are for a 98 from alldatadiy. On one of your other threads, I posted a link to the service manuals.

It gets into the weeds and I didn’t copy all of the relevant tables, so and it may be worth looking into a subscription for your 2000. Anyways, this kind of gives you an idea of what they offer.

The common factor with the tach and speedometer is the instrument cluster, so my guess would be that your issue is with that.
























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