When I start my car in the morning, I get 14.2 or 14.3 volts. The longer I drive the car, the lower the volts get. It will go down slowly (an hour or so of continuous driving) to about 12.8, with dips down to 12.2 or so. Air conditioner brings it down a point or two when running. Headlights on, also loses a point.

At about 13.4 volts I start getting codes. I've been working on these for a while now. I'm getting the P1220 code, which is then throwing me into reduced engine power. That is the killer. I've been tracking this down for MONTHS. The TB itself, the TPS sensor and all associated parts have been replaced now, so it's not mechanical. I have done all of the grounds on the car. I have checked the wire loom and the connectors with a pin, all the usual Bill Curlee recommended fixes in the long electrical thread. Still no luck. So now I noticed this. Not sure if it's related or not. I also get the Low Engine Oil message coming on. That sensor has been replaced, and the oil has been checked.

So does anyone else notice this? Is this a thing all C5's do? Do you start with 14 volts and as you drive watch the voltage go down into the 12's? Where does the 14 volts come from exactly? This is a new 12 volt battery (after replacing an optima red top to a new store bought wet cell just to see if that was the issue). As it rests, the voltage goes up? How???

 

ISN'T ELECTRICITY FUN?


Try this experiment:

Run a temporary 10ga wire from the POSITIVE battery terminal to the BATT terminal on the back of the alternator (under the black rubber boot)

Once you have that wire properly secured,, see if the voltage issue is resolved.

POST YOUR RESULTS!

BC

 

Two things, consider having your alternator bench tested to prove it is functioning proplerly.

Second, when faulty connections occur they increase in resistance as they heat up. As the resistance increases the voltage dropped across the faulty connection wil increase hence the dropping voltage. Given that this has been going on for months it would suggest that while your alternator is not yet proven fully up to spec it must be working or the battery would have completely drained by now. That said it may not be outputing the proper current level due to failed diodes or faulty regulator.

If you pull the alternator to have it tested you might want to have the battery checked at the same time. If both check out fine it's time to go through the schematic checking connections. Bill's suggestion would prove out the connection that brings current from the alternator to the battery. Past that it could be grounds etc..

 

Why not leave it,if it fixes the problem?

 

Because that's a band-aid, not a fix. If there is a loose connection at the starter, it needs to be addressed.....and could affect the starter operation. I guess it all depends how hillbilly you want your car to be.

 

I wanna be there to watch what happens when that non-fused wire gets grounded somewhere between "point A" and "point B".

 

Ok, bad choice of words.I meant until he could get the real problem fixed.

 

Whatever works for you......

 

100% correct! Thats why I said temporary! If you have a POOR connection at the starter the next thing that will happen is the terminal will melt off the solenoid. This a a method to determine if the connection at the starter is causing the issue. If GM wanted a hard wire from the battery to the alternator, there would have been one there.

If the symptoms change,, go fix the bad connections and ditch the temp wire!

BC

 

A picture is worth a thousand words.

 

Okay, sorry for the camera phone pics, but these threads are useless without good photos! Or at least some!

All grounds have been redone like this:



We did alternator side like this:



And battery side to the hot side of fuse box:



So after this the car started at 13.7 volts. Tried all power, air, radio, etc, and got it down to 13.4 where it stayed. Drove for a while, couldn't get any codes to throw other than the Low Engine Oil.



It never went below the 13.4 however, except occasionally when braking. So what does this mean? How long should I leave it on for testing? Can we put a fuse inline? What amp would that be? So where does this lead to? Is this an alternator issue or starter?

Thanks guys!

PS,

I don't mind a little hillbilly when needed:



Yes, that IS a standard beer can fix for a header exhaust leak!!!!

 

Take your alternator and battery in for testing. This will show if you have a regulator or diode problem with the alternator. It will also show what the status of your battery is. What is the battery voltage right after you shut the engine off? Did you check the engine ground strap?

 

STOP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

That digital meter reading on the DIC,,,,,,, IS NOT actual battery voltage!!!!!!!!!!! It is the voltage that the I G N I T I O N SWITCH is supplying the modules on the HOT IN RUN & START circuit. If you want to know actual alternator output,,, READ THE BATTERY TERMINALS at the BATTERY and the BATT terminal on the back of the alternator.

IF,, the voltmeter on the IPC & DIC are significantly less than actual battery voltage, you have an issue inside the ignition switch or in that circuit.

- C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html

Read and post the battery terminal voltage vs IPC/DIC voltage readings.

BC

 

Now that's good to know, Bill! Thanks!

I was wondering where 14v was coming from!

Okay, so directly on the positive battery post is 12.5 and just turning the key on, not starting engine, I get a 12.1.

Time to follow the yellow brick link to the ignition switch then?

 

The problem with the ignition switch is it may work OK one time and fail the next. Or ,,, fail after the engine is running. If you think it may be suspect, either repair it or replace it. Fail meaning in a circuit that needs a good amount of current, burnt contacts will heat up and wont allow it to receive what it needs. As it heats up, it passed less current and the voltage on that feed will drop off to very low levels.

The ignition switch also has FIVE different circuits. Three may be good and TWO may be defective.

Here's why:





BC

 

Thanks Bill! I feel like I've done everything else to no avail, so I might as well get this one out of the way, too! I will post up pics of the results!

 

Gotta love an update so soon. Bill hit it dead on yet again! If you are even in Albuquerque, NM I will buy you a beer (or three!).

Here's the mess that happens:



Here is the module:



And a close up of the badness:



So cleaning up now, and will do the tests recommended in the other thread to make sure a new one is not needed. A few things were broken, tabs and such, to get to this, leading us to believe this has been replaced before!

More when we're done!

 

Have you added any electrical loads to the car, high power aftermarket stereo, fog/driving lights etc.?

 

Has anyone tried wiring in a heavy-duty relay to power the loads from the ignition switch on those two contacts? I've seen those two particular contacts burned in a couple of pics, and it seems like the car just draws too much current for the switch to handle. Is there any room for a relay close to the switch to drive those loads?

 

So all cleaned up, the contacts now look like:



Put it back together. Drive around.

P1221 throws again as I'm driving home from work. That throws Reduced Engine Power.

Still not fixed.

VERY frustrating!!!!

So here is the list of what has been done:

Ignition switch cleaned
Battery Replaced
Grounds grounded
TPS sensor replaced
TB replaced
The loom going to the TPS has been checked. Tested the pins for grip, etc....no bare wire on the loom, etc...

What the hell else can I try? ANY suggestions will be considered!!!