Tach started working part time. Now is inoperative more than it works. Engine runs fine. Logic tells me that the "short" or problem is between the pcm and the instrument cluster panel. Anyone had this problem before? Where are the cabling and connector locations-on the car, so I can check for bad connection/chafing? I've already cleaned and tightened the G 104 ground.
Any guidance is appreciated.

2004 Z06

 

You might need this!

 

BryonHunter,

Appreciate the information. Does this indicate my voltmeter should not be working concurrently with the tach? I need a little help reading the diagram.

Thanks

 

I don't understand the question. What does the voltmeter have to do with the tach?

 

Agree With Lucky, don't worry about volt meter unless it has a problem. I would be checking circuit #121 between PCM and IPC.

 

The diagram just shows the instrument panel cluster as a black box module. If something goes wrong in the black box that does not mean everything is affected. The voltmeter is reading a voltage that the IPC receives from the IGN circuit. The tach function is getting an engine speed signal from the PCM on another line.

Bill

 

Thanks, you guys have helped me understand the diagram better. Looks like I could have corrosion at connectors under the hood at the fuse box, as well as chafed wire.

 

Did you get it fixed, what did you find?

My stock 98 w/about 75k miles has similar problems. It works more than it doesn't now, but weather seems to make it act up more. Just took a 20mile test drive for another problem and it only cut out for about a minute during the ride, no bumps or weather associated with it. The engine and everything seems to run fine, even when the tach's not working.

The code, when it wasn't working, was "Open" or "Short" as best I can remember. The tach sweeps the range when you turn the key on, even when it's not working. All the other gauges work all the time. I think G104 looks ok (if it's the one below the fuse box under the hood). The wires, when you lift the fuse box under the hood, look ok as best as I can tell.

Where's the PCM shown on the diagram?

 

Maxvtol,

No, the tach now works less than it ever did. The ground under the battery is fine. I now will look at the ground plugs under the hood, near the front. I also understand there are some sort of connections at the passenger kick panel on my car. I've been working so much that I've not had time to really sit and work with my car.

 

Thanks for the reply Raleigh. I've tried a thourough cleaning of both the grounds plugs above the front tires, no good.

I'll post if I find anything definitive.

Does anyone know where the PCM is? Only diagram I can find looks like behind the passenger front tire, under the battery.

 

Try looking under the front (firewall) part of the passenger footwell. I checked all of my connections there, for cleanliness and tightness.

 

After reading through other tach problem threads, I decided to bump the Instrument Panel Cluster and the tach started working, temporarily.

I read through this thread and pulled the IPC.

I cleaned the connector, as best I could (it looks fine to me, all the pins are straight), but when you wiggle the connector, the tach either works, peggs out, or doesn't work. All the other gauges work all the time (except I can't test the speedo yet).

Any ideas, anyone??

 

maxvtol, if you wiggle the connector, and it changes the state of the Tac, you know you have found the problem area. I take it you're talking about the connector to the IPC???
Bad wire
Bad connection where where terminal is crimped on
Female terminal spread too wide
Bad solder joint at male connection to IPC (maybe PCB)
Corosion in connector

(White Wire, Circuit #121 is where I would be looking)

 

Thanks Byron,

I took the IPC apart with the help of this thread and checked the solder joint next to the pin with a meter while wiggling the pin and seems ok.

The white wire to the IPC pin looks ok. But I can't get the wire out of the connector. There's a hole next to where the male pin goes in, but no amount of fussing with a needle or small nail can I get the white female connector out. I know it snaps in somehow. Is there a special tool or a picture of that female connector somewhere so I know what I'm dealing with. Been messing with it for about an hour now.

 

You need the service manuals, it has instructions for dissembly of the various connectors.

 

Summary:
98 coupe w/73k miles auto trans. Rarely driven in rain and maybe once in the snow.

Took it to the dealer once for the same tach problem. Found he broke a tab off the dash and alignment pin on the radio/ac trim panel. Also didn't get the IPC back together properly. Also left out several screws.

All the connectors beneath the battery and PCM looked ok. Could beat on the IPC and tach would work temporarily.

Don't know which one fixed it (check links on post #12 and #14 on how to get to this point), but here's what I did in order of probablity:
1) On the white wire on the IPC connector, I inserted a jewelers screwdriver on the bottom of the outside hole adjacent to the white female wire pin. Pulled with very firm force with needle nose on the white female pin (not on the wire). Once out, the wire to connector looked ok, so slightly squeezed the female connector for tighter fit and re-bent latch on the female pin so it would lock back in the connector.
2) Dissassembled IPC down to the circuit board. The ribbon connectors may not have been seated correctly, don't really know but pay special attention to how they come out so you can get them back in properly. The ribbons go in the connectors, and the connectors latch down on them.
3) Tightened screws on the back of the gauge (in the dissassembled IPC) that go through the ribbon connector (weren't really loose).

I can wiggle the IPC connector and beat on the IPC and tach is steady, so I think it's fixed.

 

 

i realize this is an old thread for intermittent tach, but anyone have a just plain dead tach period in a C5? My 01 zo6 tach needle just sits there and doesn't sweep or anything. luckily i have another cluster and when i plugged it in it works fine. whats the next step???

 

You had a dead tach in your original IPC. You installed a different IPC, and it works normally. Seems you have the following options:

1) Have the original IPC repaired
2) Replace the IPC

....or am I missing something?

 

yea, i know its sounds simple but i want to use my original ipc. just seeing if there was a known failure on a ribbon cable or something.
who fixes these things?