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

 

[Dirt Ferguson]

I know the gauges on these vehicles can be a littly wonky, but my battery voltage gauge started consistently reading under the 14V mark. I've also had some odd electrical issues pop up in the last week. I have no idea the last time the battery was replaced. Probably time to start there and see if it makes a difference?

My current battery is a Toyota battery. Will switch it out with a 27F Interstate from Costco.

 

[2001LX]

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.

What was the solution? I'm getting the exact same problem.

 

[2001LC]

When we see the Dash battery meter pushing up near 18V. It usually mean alternator need replacing. We check to see if same voltage, read at battery, with multimeter. We also check all wire to and from alternator to/and battery and those from battery to/from fusible link. All good and see battery matching (18 volts) dash gauge. This indicates over change, due to fault in alternator. Overcharging alternator, usually burns up the battery.

If on the other hand, Battery reads ~13V and dash gauge ~18V and wire/connections all look good. Likely a gauge issue. We can look at actual volts, in tech stream. If its data also reads ~13V. This further points to dash gauge issue.

 

[2001LX]

I initially measured around 16V at both the battery and the dash gauge. Shortly after, the alternator failed and stopped charging (voltage dropped to battery level, and the engine would stall if the battery was disconnected). I replaced the alternator, but after about 20 minutes of driving, the same failure occurred: the battery gauge spiked, followed by alternator failure. On the second replacement, I also installed a new battery. Everything seemed normal at first, but the battery gauge eventually spiked again, and the battery warning light illuminated. This time, the alternator continues to charge at 14.3V, but the battery light remains constantly on.


The battery terminals and fuse blocks show no corrosion or rust, and all fuses have been checked and are functional. One additional issue I’ve noticed is that the AHC (Active Height Control) system is no longer operating.

Battery wiring for future reference: https://st.club-lexus.ru/attach/u/73155338eaae12f559c39045c9fadc8a.pdf

 

[2001LX]

After changing the alternator for the third time, it seems that the problem is fixed!