Help Needed: GX Died After Battery Swap / Low Voltage / No A/C — Alternator or Fusible Link?

[yosshaa]

Hey everyone — looking for some help diagnosing an issue on my 2019 GX460, about 117k miles.

I’m supposed to leave for a two-week road trip soon, so the timing is not ideal.

The GX was just at Lexus for an oil change and general checkup. I asked them to test the battery while it was there. They told me the battery needed a charge but otherwise tested fine.

A few days later I was working on hardwiring a dash cam using power near the rain sensor. I was working on it for an hour or two because I was getting some odd behavior and could not get the camera to power on correctly. When I checked the wires with a voltmeter, I was only seeing about 8–9 volts. I then checked directly at the battery and saw the same thing.

I started the GX and the voltage continued to drop. I went inside to grab my wallet because I figured I needed to go buy a battery, and by the time I came back out, the truck had died.

I pulled the old battery, jumped in my wife’s car, and bought a new X2Power Group 27F AGM battery. Installed it, and the GX fired right up, but then died. I started it again and it seemed to run, but now the A/C will not come on. The A/C button lights green for about three seconds, then shuts off. I tried the HVAC reset procedure, but no change.

I also disconnected/reconnected the battery terminals thinking maybe it needed a hard reset after the battery swap. Still no fix.

Current voltage readings:

• Around 11.8–11.9V while idling
• Drops to around 11.3V with accessories running
• The truck has died again after restart, so it seems like it is running off battery only and not charging.

I ran a scan and got several codes:

Engine

• P0335 — Crankshaft Position Sensor “A” Circuit

A/C

• B1422 — Compressor Lock
• B1449 — Air Outlet Damper Control Servo Motor Circuit, Rear

Other

• B15DB — Telematics Transceiver Disconnected
• U0233 — Lost Communication With Side Obstacle Detection Control Module, Right
• C1AEC — Front Sensor Communication Circuit
• C1AED — Rear Sensor Communication Circuit
• Several additional telematics-related codes

At this point, I’m thinking the alternator may be bad. It could just be time — 7 years old and 117k miles — or I’m wondering if I may have damaged something during a winch install a couple weeks ago. I’m also wondering about the main fuse/fusible link between the alternator and battery.

Before I throw an alternator at it, what would you guys check next?

My current plan is:

1. Fully charge the new battery.
2. Check voltage at the battery with the engine running.
3. Check voltage at the alternator B+ stud with the engine running.
4. If the alternator shows 14V but the battery does not, chase the fusible link/charge wire.
5. If the alternator also shows 11–12V, assume alternator or alternator control circuit.

Does that sound like the right diagnostic path? Also, would a charging-system failure explain the A/C compressor lock code and the A/C button shutting off after a few seconds?

Any help is appreciated. Trying to get this sorted quickly before the road trip.

 

[Bang Bang]

After the battery has been disconnected, the first time you try to restart, it will fire up and immediately die. That is normal. As for the other issues, I would tend to think it's the alternator that needs replacing. I would bring it to the auto parts store and let them load test the battery and alternator.

Also, after doing a quick Google search, I would think that all the codes except the P0335 will all be addressed by fixing the electrical issue. The P0335 may as well but you may need to do like Schwooby and swap that sensor.

Thread '2010 Lexus gx460 throwing p0335 code'

Jun 23, 2026

This seems to be the crankshaft position sensor. I cleared the code to make sure it wasn’t a false thing after checking my gas cap.

My CEL, 4lo light, center diff light are all flashing. My dash display is also dark now.

Anyone dealt with something like this before?

• Schwooby
• Replies: 3
• Forum: GX460 / Prado150

 

[Rednexus]

Agree on the alternator. It should be generating 13-14 volts when running. If it's generating far less than that at the battery cable lug on the alternator, the alternator is damaged. The alternator probably crapped out and killed your battery to start with. The alternator hangs low on a GX to start with, 117K is not an unreasonable lifespan for one. I would however re-check your accessory wiring and possibly disconnect it while you complete troubleshooting.

If it is your alternator (which I think it is), you may have to settle for a non-OE Toyota/Denso replacement given your upcoming trip. Most any parts store can get you a new alternator in a day, if they don't have one in stock. I'd suggest getting one from NAPA - they might be able to get an actual Denso reman. Even if it's not a Denso reman their remans are usually a bit better quality than the other big chain stores.

 

[yosshaa]

Confirmed its the alternator... replacing with a 240 amp alternator, lucky to find it in town: 2019 Lexus GX460 4.6L V8 Alternator | Tucson Alternator - https://www.tucsonalternator.com/product/822829/2019-Lexus-GX460-4.6L-V8-Alternator/3-ORG/

not expetced but probably good to get the bigger alternator and bigger battery considering the new winch and road tripping with a plug in fridge.

 

[Rednexus]

Confirmed its the alternator... replacing with a 240 amp alternator, lucky to find it in town: 2019 Lexus GX460 4.6L V8 Alternator | Tucson Alternator - https://www.tucsonalternator.com/product/822829/2019-Lexus-GX460-4.6L-V8-Alternator/3-ORG/

not expetced but probably good to get the bigger alternator and bigger battery considering the new winch and road tripping with a plug in fridge.

If you have not already, you really should do Big 3 wiring upgrade with a 240 amp alternator. The OEM hot wire from the alternator to battery is only around ~10 gauge and unfused. If there is a big enough draw on the upgraded alternator (i.e., running the winch with the engine on), it can melt that tiny wire and possibly burn your rig down. I used 1/0 gauge wire for my Big 3 upgrade and DIY'd the cables/ends, but you can also buy a pre-made kit. This is also a good time to upgrade battery terminals if you have not (I like SDHQs myself, and they are another local vendor to you).