Voltage issue

So I was driving today and the check gauge light goes off and the voltage gauge jumps up to 19v! It stayed there and the trans wouldn't downshift! I pulled over and shut it off and restarted it. Everything was fine for a while. I wheeled for about 1-2 hours and it was all good... Got back to the faster part of the trail and it started going crazy again. The dash lights get super bright and then dim while it shows 19v! Any idea guys? It's a 97 4.0l auto btw

Stop driving it....... Take the alt out and have it tested. Battery to at this point as you've been driving it. Your alt is overcharging the battery. The internal regulator is bad.

Seems I have heard of this before, and it was a bad ground.
Regulation is done by the PCM, not the Alt.

Try cleaning battery grounds at chassis and make sure they are good at the battery., Also the strap which connects the engine to the chassis.

Check the nut at the end of the PDC under the cover.

Just a wild guess, but pull the fuel pump relay and look at the pins, are any discolored blue or black? The PCM and the fuel pump share a power source, if the fuel pump is sucking down the power it seems possible the PDC would try to compensate.

That 19 volts sure sounds familiar, but I'm old and the old brain just doesn't work like it used to.

If you have low voltage going to the dark green and black wire at the PCM, for whatever reason, it is likely you will get high charging.

If you have a short in the alternator near the end of the windings, it is likely you will get high charging. You may be able to pick this up checking the ground at the case with the battery negative ground, using your low scale volt setting. You'll typically get a little voltage like 0.2-0.3 volts anything higher and something is wrong.

It may be the voltage regulator built into the PCM is taking a dump and there isn't much you can do about it. They say if you arch the B+ (dark green and black) wire at the PDC multiple times or even the battery terminals multiple times (with the key in the run position), it can scramble the brains in the PCM and mess with the program. I really don't know if it is fact or fiction, but I'm pretty careful about arching the battery terminals multiple times when I put them back on and make sure the key is off.

You should have stored codes that may put you on the right track. At least three different alternator failure codes (if I remember correctly) that may help narrow down the exact problem.

WB9YZU said:

Seems I have heard of this before, and it was a bad ground.
Regulation is done by the PCM, not the Alt.

Try cleaning battery grounds at chassis and make sure they are good at the battery., Also the strap which connects the engine to the chassis.

Click to expand...

The strap which connects the engine to chassis was broken... Will drive tonight and confirm that was the issue

Reviving this old thread cuz my 2000 just did the CHECK GAUGE and 19V on the meter thing. Had been sitting for most of the winter, jump started it yesterday, ran fine for 4 or 5 minutes sitting, then it happened. I shut it down and it was dead again when trying a restart.
Alboy, did you get the problem resolved?

Never mind. Used my search-fu and found a bunch of possible fixes and things to check. All sounds like fun too...not!:laugh:

Reviving this old thread. My 1997 just did the red "check gauges" and the volt gauge went to 19V. All other gauges were normal. This is my dd. All went back to normal when I made a turn off the main road. The second time, it went back to normal when I pulled over and left it idle. I cleaned battery terminals 30 days ago as it was not turning over normally when starting. Will check codes and that ground strap tomorrow.

Ricker said:

Reviving this old thread. My 1997 just did the red "check gauges" and the volt gauge went to 19V. All other gauges were normal. This is my dd. All went back to normal when I made a turn off the main road. The second time, it went back to normal when I pulled over and left it idle. I cleaned battery terminals 30 days ago as it was not turning over normally when starting. Will check codes and that ground strap tomorrow.

Click to expand...

Codes are P0340 and P0118 wtf? Still showing high volts on the dash gauge at times with the red check gauges light, but 12.8 to 14.4 at the OBD2 port via my Scangauge (a little higher than normal). The negative battery cable seems hotter than than positive cable at the battery. No unusual odors under the hood, battery is not hot or venting fluid. I'm leaning towards a bad cable or a weak battery. Load test showed 11.8 v with headlights, radio and ignition on for 5 minutes.
Any suggestions?

The voltmeter, like all the gauges on the dash are outputs from the PCM fed though the communication bus and decoded by the dash.

Your Voltage is also regulated by the PCM as a direct input to the field winding of the alternator.

What is at the port may be a regulated voltage, not unregulated system voltage.

Most often, a high voltage reading is due to the PCM loosing it's ground reference. Check your grounds from the batter to the Chassis and the Chassis to the Engine. Also check your PCM mounting and grounds on that side of the vehicle.

-Ron

Yes, it was the ground wire at the battery. All is good now.