c5_pewter_vette

I've search the forum for this problem but I haven't found anything similar.

I have a 2001 coupe. I was driving home from the airport the other day and my engine just stopped. The headlights still worked and the dash lights still worked (it was at night). The door locks made a "click" sound when the failure occurred. I guess the car was unlocking the doors. I coast to a stop (with all lights fully operational) and restart the engine with no problems and drive home.

Today, I finally have a chance to look at the car. Placing the ignition in the "ON" position displays zero volts sometimes and 12VDC+ at other times. When it reads zero the car will turn over strongly but won't start. When it reads close to normal the cars starts as expected. The in-dash voltmeter needle actually jumps erratically yet a voltmeter on the battery shows a good charge. During all this, the headlights and underhood light are bright and strong. The dash lights and interior chime, however, are erratic. The computer is obviously suffering from undervoltage and is complaining about all kinds of issues. The battery is fairly new and is holding a charge as measured with a voltmeter across the terminals. The in-dash voltmeter reads OK when the engine is running BUT the digital display shows the voltage periodically dropping to 10-11 volts for just a split second.

I don't have a schematic of the electrical system. The symptoms are like there are two electrical circuits operating differently. One with the headlights, etc... that works fine along with the battery. The second one is intermittant and controls the interior lights, dash lights, computer(s), and the spark, etc... part of the ignition system.

Could this be the TAC module? A found information during a forum search about bad TAC modules but the symptoms don't appear exactly similar. I'm not sure what the TAC module does.

I think the key symptoms that will pinpoint the problem are 1.) Headlights OK and good voltage across the battery and 2.) bad voltage displayed on dash voltmeter. Whatever is between the battery terminals and the point in the circuit where the in-dash voltmeter read the battery voltage is either loose or defective. Anyone have an idea what it could be?

Thanks.

Bill Curlee

The TAC module is most likley not causing this issue. Sounds to me like your have a loose connection and are loosing power to the electrical system or some modules. Check your codes and let me see what DTC codes are set.

There are some key areas to inspect, clean and tighten before you start replacing stuff and driving your self crazy. Believe me, Ive been down this road before!

Here is where I would start.
- Remove the battery cables. Spray each cable end terminal out with brake parts cleaner and then spray them out with WD-40. Torque them back on with a torque wrenck to 11 ft/lbs.

The battery cable on the starter solonid is known to come loose and cause electrical issues. While you have the battery cables disconnected, check that connection. The ground connection for the engine is down in that area too. It's forward and above the starter. Make sure that it is tight also.

Another common problem area is the chassis ground connectors. read this post that I started a while back and clean your grounds.

http://forums.corvetteforum.com/show...ion&forum_id=1

Please let me know if this info helps you.

Bill C

c5_pewter_vette

Hi Bill,

I can't retrieve any codes since there isn't enough power to run the computer. Headlights work great though. I did tighten (but not clean) the battery connections with no luck. I get plenty of juice from the battery it's just not getting to the circuit that runs the dash lights, computer, etc... and part of the ignition system (starter works fine - engine turns over strongly but no start).

The voltmeter in the dash supposedly measures battery voltage when the ignition is in the "ON" position. Do you know where that voltage is measured? The voltmeter reads zero while the voltage at the battery terminals read 12.22 volts. I believe the circuitry between those two points contains the source of the problem. I just don't know what it is yet.

Thanks!

c5_pewter_vette

Could this be caused by a relay? I looked at the car again this morning and now the car sometimes starts. The voltage is very low sometimes when I turn the ignition to "ON" but after 3-4 seconds the voltmeter in the dash goes to normal and the car will start. During the 3-4 seconds it sounds like a relay (or relays) next to the battery is chattering.

How do you remove (unplug) a relay?

Thanks.

vettenuts

How old is the battery? Any evidence of leakage (did you remove the battery and look?

c5_pewter_vette

I found the problem. It turned out to be the ignition switch.

I found a resource on the web alldatadiy.com which had service info for the Corvette online. Probably you guys had heard about the website but it was news to me.

Anyway, I went through the schematic and followed things back from the in-dash voltmeter and found that the IGN relay (Relay 42) was not energized. I found that Fuse 47 of the I/P Fuse Block inside the car had the correct voltage but Fuse 15 did not. This indicated that one section of the ignition switch was defective. I jumpered across the switch to verify the diagnosis and everything starts to work. The next thing I need to find out is if an ignition switch is something that I can replace myself.

Being an EE, I'm glad I had an electrical problem. If it had been a major mechanical problem I would have been out of luck.

Thanks guys for the help!