C5 Tach Problem
Thread Starter
6th Gear
Joined: Jul 2004
Posts: 6
Likes: 0
From: wilson nc
C5 Tach Problem
I have a 98 white M6 coupe. Starting having a tach problem last week.
While driving, the tach started "fluttering". This lasted for a few days. Now this week, first day I drove the car and the tach worked perfectly.
Very next day, the tach will not work at all and has not worked since, with the engine running. But, when you turn the ignition to start the car, the tach will cycle normally back and forth as it should. Checked all fuses and look O.K. Checked codes for tach signal board fault and did not find any. Any ideas folks? Remove dash maybe to check for loose connection to tach?
While driving, the tach started "fluttering". This lasted for a few days. Now this week, first day I drove the car and the tach worked perfectly.
Very next day, the tach will not work at all and has not worked since, with the engine running. But, when you turn the ignition to start the car, the tach will cycle normally back and forth as it should. Checked all fuses and look O.K. Checked codes for tach signal board fault and did not find any. Any ideas folks? Remove dash maybe to check for loose connection to tach?
Drifting
Joined: Jun 2004
Posts: 1,887
Likes: 2
From: Havin' fun in Frederick, MD!!!
St. Jude Donor '05 '09
I took a look in the schematics for this, but it either doesn't go to that level of detail, or I don't yet know how to interpret them to find that detail. Sorry I can't help beyond this point, but I suspect there is someone here who can. Good luck.
Drifting
Joined: Jun 2004
Posts: 1,887
Likes: 2
From: Havin' fun in Frederick, MD!!!
St. Jude Donor '05 '09
The "Instrument Panel, Gages and Console" section of the service manual has a troubleshooting guide for the tach but it is pretty limited. There are 4 steps to it, the first asks if you performed an IPC diagnostic. If you have not it directs you to that step. The second step tells you to compare the diagnostic tester output with the tach output. If it does not, the third step tells you to replace the instrument cluster. The fourth step tell you to operate the system and verify the replacement corrected the problem. So much for detailed troubleshooting.
Again, good luck.
Again, good luck.
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Don't have this problem with mine, but will be watching this thread to see if anyone has a solution to this issue. 
Melting Slicks
Joined: May 2007
Posts: 2,014
Likes: 80
From: San Antonio Tx
My HUD acts up at the same time my tach does... today it died driving down the road... got home turned car off and back on... working perfect... I have shift light installed so I double checked this connection as its connected directly to the tach... problem seems to be ok but will update this as more info comes... car will be at shop thurs for dyno.. see if we can break the 808hp mark ** true test for the tach **
Le Mans Master
Joined: Dec 2004
Posts: 5,789
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From: Myrtle Beach SC
St. Jude Donor '05-'06
Does the tach sweep normally at turn on? GM IP motors are notorious for going bad from that era. They have replacements that are better but I tried doing it in a sunfire and it did not work. I guess my soldering skills weren't up to the task. After doing an IP diagnostic you will probably need to either send it off for repair or replace it.
Last edited by Redeasysport; Mar 28, 2011 at 10:56 PM.
Melting Slicks
Joined: May 2007
Posts: 2,014
Likes: 80
From: San Antonio Tx
Yep does initial sweep no catching no problems nothing and It's usually at low rpm while cruising Ie 70mph in 6th gear I'm at 1900rpm if I keep them above 2500 ish no problems arise.... usually its high rpm ''after all the research'' that people see this problem...
Le Mans Master
Joined: Dec 2004
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From: Myrtle Beach SC
St. Jude Donor '05-'06
Still doesn't mean the servo motor isn't going bad. They can be very intermittent at first. The one I observed ended swinging all the way around and jamming the speedo. What does yours do just drop out? Is it accurate the rest of the time?If so in a C4 there is a "Tach filter" that was notorious for going bad. It had capacitors in it that died. I still do not know enough about the C5 Tach ckt to give you a good answer other than the possibly bad servo at this point I will see what I can find out......
Le Mans Master
Joined: Dec 2004
Posts: 5,789
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From: Myrtle Beach SC
St. Jude Donor '05-'06
http://forums.corvetteforum.com/c5-t...ermittent.html
I think your answer may be here It appears the PCM sends a signal to the IP no filters juat a straight shot so either PCM or IP(servo?) is bad. Damn computertized crap.
I think your answer may be here It appears the PCM sends a signal to the IP no filters juat a straight shot so either PCM or IP(servo?) is bad. Damn computertized crap.
Last edited by Redeasysport; Mar 29, 2011 at 02:14 AM.
Le Mans Master
Joined: Dec 2004
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From: Myrtle Beach SC
St. Jude Donor '05-'06
