100 Series Battery Gauge Spikes (1 Viewer)

[ghong14]

Hi Fellow IH8MUDers,

Started to notice that the battery gauge on my 98LX470 started spiking towards 18V when I turn on the car. The spike correlates with increasing the RPMs as I drive the vehicle. The Battery lights is turning on as well. After driving the car for a bit the gauge goes back to normal and the battery warning light also turns off.

I had a Denso alternator replacement put in this car just a year ago. Looks like this vehicle model fits the 12V version. Also replaced the battery last week, didn't solve the issue.

I did some research and saw that this may be a result of voltage regulator getting shot. Thought I get everyone's thought.

 

[Biga27110]

Interesting I will be following along. I'm sure others will have an answer.

 

[94SRUNNER]

This looks like it may be a failing alternator. I suggest stopping by a auto parts store and have them test your alternator and battery to be sure.

 

[JunkCrzr89]

this may be a result of voltage regulator

That is indeed the problem.

 

[jerryb]

junk is the new magic 8 ball. haha
Additives are useless.
Correct, not wrong.
That is indeed the problem.



Mr crzr, do you think injector clicking, combo meter stepper motors, and valve shims have the same clicking sound if out of bounds?

 

[JunkCrzr89]

Mr crzr, do you think injector clicking, combo meter stepper motors, and valve shims have the same clicking sound if out of bounds?

No. dB and pitch differ.

 

[ghong14]

Hey guys still need some help here. My mechanic swapped the alternator (denso) and the battery. Same issue reoccurred after leaving car parked overnight. When I turned on the car this morning, dismayed to see the voltage gauge up again.

Could this be a fuse issue? Seems to reoccur after parking the car for a while then goes away
After you drive or leave the engine on for 5 mins.

 

[jLB]

I assume that you are only seeing this when the engine is running?

If you assume that the voltage regulator is working properly, having replaced the alternator, my guess would be a bad connection on the “ALT-S” line.

 

[ghong14]

I assume that you are only seeing this when the engine is running?

If you assume that the voltage regulator is working properly, having replaced the alternator, my guess would be a bad connection on the “ALT-S” line.

What is the ALT-S line?

 

[jLB]

What is the ALT-S line?

It’s a connection between the alternator and battery, that the alternator uses to “sense” the battery voltage.

Sometimes a diode is used on this line, to boost alternator output for AGM batteries.

I also know that the alternator plastic connector/plug has a tendency to crumble, so that’s probably where I’d start looking. The second place would be the 7.5a fuse on the line, marked “ALT-S”.

 

[Biga27110]

This might sound silly but have you taken a volt meter to the battery while the engine is running to verify the gauge is not faulty.

 

[ghong14]

This might sound silly but have you taken a volt meter to the battery while the engine is running to verify the gauge is not faulty.

Yes I have. When the volt meter in the car spike it also shows on the external voltmeter. The result is ~17V than the normal 14V

 

[Biga27110]

Yes I have. When the volt meter in the car spike it also shows on the external voltmeter. The result is ~17V than the normal 14V

I expected it to be fixed with a new alt and battery. I'm very curious as to what's going on and the solution.

 

[ghong14]

I expected it to be fixed with a new alt and battery. I'm very curious as to what's going on and the solution.

Mechanic first switched the alternator with another Denso. Same issue. So he swapped the battery. Problem went away when he checked. Picked up yesterday. Same issue this morning.

 

[Biga27110]

@2001LC @FxFormat