CVetteLuver

My 91 C4's dash gauges stopped working. Only the speedometer works.....the tach always reads 6000 rpm's when driving....all the other gauges are frozen still. Does it need a computer part or what?

leesvet

check the grounds for the instrument panel. Often its just a dirty connection or a loose plug. Grounds are always the first place to go when something electrical acts strange on a Corvette. Might want to go thru the fuses also..

OkieC4

Check your 5A CLSTR fuse in the main fuse panel, then the G201 ground beneath the l/h side of the IP on the kick panel.

FSM 8A-82-0

383vett

One important ground for the ip is on the bellhousing to block bolt, driver's side, middle of the three. If that is off, the ip will not work correctly.

CVetteLuver

Thanks everyone for the suggestions/ideas....will check all of those areas today

leesvet

yes...that ground bundle on the trans bellhousing is the single most important of all. There are at least 4, maybe 5 ground wires there. The ecm and instrument wire is in that stack. There is also a lt ground strap from the block to the frame in that same area.

Look at the "jumping" terminal behind the battery for loose connections. These are the fusable links to all the sub-systems inside the cabin.

CVetteLuver

Still checking...fuses are good.Oh, and I have no interior lights either,except when the rear hatch is open! Will check gound wires underneath after I jack it up.

OkieC4

Per the FSM, the common grounds for those systems are G106 at the gang above the oil filter, G201 and G202 on the kick panels below each side of the IP.

Do your courtesy lamps work from the light switch?

CVetteLuver

Yes, the courtesy lamps work from the light switch, but now since I've pulled and checked fuses.....the center speedometer dial where it shows mileage, fuel, ect....is blinking like crazy...from metric to eng....back and forth while I'm sitting still at idle!!! Geeze, do I have to do to a dealer mechanic and get ripped off for repairs?

OkieC4

Check the G201 ground behind the l/h kick panel under the IP. Otherwise, I would check the connectors at the CCM.

Also, this sounds kinda silly, but try pushing in on the left lower side of the cluster to see if the IP is fully seated in the socket or giving the dash pad a slap directly above the lcd to see if you have a loose pin where the lcd plugs in to the IP connector....

0KEN W ANDERSON

Sounds like a bad CCM/BCM. Have you recently jump started your car?
A battery jump box is sudden death to this computer.

CVetteLuver

Yeah, sounds silly, but it worked after I slapped the top center of the dash out of anger, and it stopped blinking and it showed current mileage, fuel level, and tach ideling incorrectly at 4k. Other gages not working at all.

I'm not familiar with this C4 at all, but I'll try looking behind the kick panel.

MyFirst90coupe

When I bought mine the Speedo / fuel screen barely displayed and the tach was dead. I took the IP out and cleaned all of the contacts with rubbing alcohol. The Speedo / fuel screen works like a champ now. I'm convinced that my tach is just dead. Have another cluster on the way to fix that.

anyway, my suggestion is to pull the cluster and clean contacts. It can't hurt and only takes about 30 minutes.

Good luck!

OkieC4

Yeah, it figures, the pins on the LCD either build a little corrosion or wear over time and get loose in the small connector coming off the IP circuit board.

Are your cluster "panel lamps" (backlighting) working?

As far as the gauges not working, it's time to pull the IP cluster out and check the "plug in" connector on the dash.

After you get the IP clusted out, using a test light or a voltmeter, on the IP dash connector, bottom row, counting left to right, the first pin on the l/h side (A1) is the ground for the gauges and lights. Connect a test light (or voltmeter) between A1 and A4 (fused power feed). Turn on the key. Test light on or VM showing 12V? Yes, car circuits and fuses are ok and problem is in the IP circuit board. No light or volts, A1 is the ground which ends up at G201 and A4 is the power feed from the CLSTR fuse to the gauges when the ignition switch is on.

Next try A3 to A1. If you have power, then the CLSTR fuse and ground to G201 are good.

A3 is the feed for your backlighting...... but the CCM controls the dimming.