90 Grand Prix issue... gauge cluster issue

[StealthWyvern]

Hey guys! I’m currently helping a friend fix up his old ladies car so she can have something decent to roll around in. So far we have fixed roughly 90% of all the issues. Theirs just one thing that im not 100% sure about. It’s a 1990 Pontiac Grand Prix 3.1 v6 auto coupe. SE(I think). The issue that im having is the gauge cluster! Everything works on it like normal except the tach and speedo. You can be doing 20ish and the speedo will state your going 120mph! Also it “idles” at 5.5k. I know it doesn’t due to the sound and my scan tool. Any ideas what this issue could be? All fuses are good, no codes. Also when you come to a stop the speedo reads 0mph.



Edit: The tach or the speedo always apear to read like 5 times of what the actual speed or rpms are.
Edit2: The car runs, drives, and shifts fine also

[sunlightsilver]

The tach I am not sure on, but the speedo problem could be the pick up in the transmission. Check for corrosion, broken wires, if that is all good and it is cheap enough replace the sensor.

[StealthWyvern]

The tach I am not sure on, but the speedo problem could be the pick up in the transmission. Check for corrosion, broken wires, if that is all good and it is cheap enough replace the sensor.

its a electronic guage cluster.. I'm thinking it might be the ECU becuase the low gas light is on even with a full tank , and it does say check gauges thats all lit up. I'll check the grounds once I have a chance to look at the car.

[sunlightsilver]

It very well could just be a grounding problem, check the ground strap from the frame to the motor, other than that it might be the sending unit for the gauge cluster.

[zoom zoom maz6]

time to start checking out the lower body harness.

could be a bad ground........

could be a fried cluster..... it is 19 years old after all. spend 10 mins in the Junkyard and you should be able to find one.

as for the speedo reading wrong. check your speed sensor and clean it. should fix things up.

in the early 90s gauge clusters didnt interface much with the ECU..... So I dont think you have an ECU issue. back in the day(how Ironic it is to say about something younger than me) things were run more on relays and fuses, than being fused into the ECU.

[jw116]

ok. so. i have exactly the same problem. i took the entire dash console out to see if any circuits were fried. thats a big negative. so where is this so called speed sensor located? cause this is kindof important to fix. thanks for the help!

[StealthWyvern]

ok. so. i have exactly the same problem. i took the entire dash console out to see if any circuits were fried. thats a big negative. so where is this so called speed sensor located? cause this is kindof important to fix. thanks for the help!

If its the exact same problem and car as my friends its here.
http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c15280067e60


P.S. We haven't gotten around to trouble shoot anything on her car yet. Some people say check the ground on the ECM/PCM which is under the fuse panel in the engine bay.

[zoom zoom maz6]

linky isnt working stealth

here is one that works (http://cgi.ebay.com/ebaymotors/Speed-Sensor:1988-92-Pontiac-Grand-Prix,Buick,Chevrolet_W0QQitemZ390025692733QQcmdZVi ewItemQQimsxZ20090121?IMSfp=TL0901211510010r10454)

[zoom zoom maz6]

should be on the transaxel somewhere......