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Salvage 2022 Model Y LR. High Voltage Battery contactors not closing. Car has the new Li-Ion 12v battery.

Hi All,

The car had a rear end damage (R Bumper, Liftgate):

1. Pyro fuse was blown: Have replaced
2. Driver side Seat belt restraint stuck: Not yet repaired/replaced
3. All Airbags are good

  • After the Pyro fuse was replaced, the charge port light has turned from Red to Blue but the car still won't charge. Occasionally I am able to click on the screen to “Start Charging”. The button momentarily turns gray (unclickable) but doesn’t charge and then the button returns to active but not clickable anymore. The car shows maintaining 260 miles of charge
  • The 12v battery drains and dies in few minutes with these messages. I also got a new 12v Li-Ion battery from Tesla and that too died shortly. Now I am using an external Lead Acid.
    • VCFRONT_a478 Schedule Service – Vehicle may not restart
    • VCFRONT_a402 Electrical system backup power is unavailable - Vehicle will consume more energy while idle
    • VCFRONT_a192 Electrical system is unable to support all features – shutting down features to conserve energy
    • VCFRONT_a191 Electrical system power reduced - Vehicle shutting down
  • On connecting the 12v battery, I can hear the usual low sounds and the screen turns on. I can put the car in “Transport Mode” and the EPB works fine.
  • But I do not hear the High Voltage Battery contactors closing sound and this is the likely the problem (and so the message VCFRONT_a402 Electrical system backup power is unavailable)
Trying to figure out. Didn't find any shorts or severed wires (except for the parking sensor harness on the Rear bumper which has been disconnected).

Appreciate any Help.
 
  • Informative
Reactions: JonB65
Made some progress.

I noticed that upon applying the brake, only one (left) tail lamp lit up. Checked the right one and didn't see any obvious physical damage. Nonetheless, disconnected it and connected a fully charged Lead Acid 12v Battery (12v Li-ion battery remained connected though no activity). Between all the startup sounds, amazingly heard the HV contactors close.

I was able to start charging. The Air conditioner kicked in.

The Li-Ion battery isn't charging though and I am still getting all the alerts and also a VCFRONT_a746 Low voltage battery disconnected - Reconnect low voltage battery.

I measured the voltage between +ve and -ve terminals on the car and it at 13.7v

I will leave it overnight to see if by any chance the High Voltage battery charges the 12v battery.

The Li-Ion connector has 5 terminals (Pin 1 is +ve, Pin 2 is -ve, Pins 3 & 4 seems to be an interlock loop that terminates on the connecter itself - Green tab with two contacts when checked with a multimeter has continuity and Pin 5 connects to a thin green wire going to the car).

Battery voltages between +ve and -ve is 13.6. Between -ve and pin 5 is 11.6, -ve and either 3 & 4 is 0.

The Li-ion battery likely has a memory or something. After pin 5 drops below 12v, the car doesn't make any effort to draw power from it. I charged the original Li-Ion battery that came with the car. Voltages between +ve and -ve is 14.5. Between -ve and pin 5 is 12.6. Connected it but the car remains lifeless.
 

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  • Informative
Reactions: JonB65
Made some progress.

I noticed that upon applying the brake, only one (left) tail lamp lit up. Checked the right one and didn't see any obvious physical damage. Nonetheless, disconnected it and connected a fully charged Lead Acid 12v Battery (12v Li-ion battery remained connected though no activity). Between all the startup sounds, amazingly heard the HV contactors close.

I was able to start charging. The Air conditioner kicked in.

The Li-Ion battery isn't charging though and I am still getting all the alerts and also a VCFRONT_a746 Low voltage battery disconnected - Reconnect low voltage battery.

I measured the voltage between +ve and -ve terminals on the car and it at 13.7v

I will leave it overnight to see if by any chance the High Voltage battery charges the 12v battery.

The Li-Ion connector has 5 terminals (Pin 1 is +ve, Pin 2 is -ve, Pins 3 & 4 seems to be an interlock loop that terminates on the connecter itself - Green tab with two contacts when checked with a multimeter has continuity and Pin 5 connects to a thin green wire going to the car).

Battery voltages between +ve and -ve is 13.6. Between -ve and pin 5 is 11.6, -ve and either 3 & 4 is 0.

The Li-ion battery likely has a memory or something. After pin 5 drops below 12v, the car doesn't make any effort to draw power from it. I charged the original Li-Ion battery that came with the car. Voltages between +ve and -ve is 14.5. Between -ve and pin 5 is 12.6. Connected it but the car remains lifeless.
Okay, so this is what I learnt:

Pin 5 on the battery is a LIN pin communicating with the car. When the car (master) senses Low Power, it sends a SLEEP MODE COMMAND to the slave (12v Li-Ion battery) to go to a "Low-power mode operation" and disables the LIN Bus. The battery MCU is still operational and the LIN can receive commands but cannot send until a wake-up event. Due to this, the battery won't even charge (unlike Lead Acid) even if the the car is now running, or you have the charger connected or the HV battery is supplying power.

Two choices at this point:
1. Wake-up the battery LIN (which I haven't figured yet)
2. Buy a new 12v Li-Ion battery from Tesla (obviously it will have the LIN communicating) even though your battery isn't dead/bad. It's just on a low power protection mode.

I see two Potential Problems:
1. Similar to my case, in an accident, the Pyro fuse will blow and HV battery will disconnect. The 12v Li-Ion will last you 30 minutes and then go to sleep unless you disconnect it. I saw that the car does warn how much power is left on the 12v until 5% remaining and then shuts off.

2. For any reason (maintenance or so) you disconnect the HV First Responders' Loop but leave the 12v connected, you should watch the car's screen and not let the 12v go to sleep.

I have a Model Y from Dec 2021 that has a 12v Lead Acid. The car in the above reference is a Model Y from Jan 2022 and has this new 12v Li-Ion. So I am assuming all Model Ys after Jan 2022 may have the Li-Ion 12v.

Thought I should share. Hope this helps some one..
 
I suspect this has nothing to do with the 12V battery. The car refuses to close contractors for some reading, but issue with 12V battery should not be one of such reasons.

Check the resistance on the new pyrofuse, it could be defective. Or maybe you forgot to plug in that small cable into it?

And just in case check to make sure the charge computer is not damaged.
 
  • Like
Reactions: ATPMSD

ATPMSD

Active Member
Mar 12, 2021
1,317
1,203
Atlanta, GA
I suggest if the HVAC is running then the HV contractor has closed as the HV system runs the HVAC, heater and drive train. However, there is also a DC-DC converter that supplies the 12-volt system when the contractor is closed. If you have a problem there then the entire 12-volt system is ruining off and draining the 12-volt battery,

Some of the errors noted, such as ”VCFRONT_a192 Electrical system is unable to support all features” seem to point to something like this.

Good luck!
 
  • Like
Reactions: mba83

ATPMSD

Active Member
Mar 12, 2021
1,317
1,203
Atlanta, GA
you can’t run the car solely off the 12v battery,

Well sort of. As I understand it if the 12-volt battery is to low you cannot wake up the car since there is not enough power to close the contractor to bring the HV battery online. But if the contractor is closed the car will run off the DC-DC converter, and if that is not working then it will run off the battery. In that case once the battery dies everything on the car will stop working, but the should still be drivable since the drive train runs off the HV battery. Of course the screens will be blank, stop lights and turn signals will not work, etc.

Just as an alternative to your suggestion, I keep this in my car as a backup jumper (I can’t easily tell if your suggestion requires a 120-volt connection, this one is self-contained):

 
Yes the battery may not have enough power to get the car to fully boot up - including closing the contactors.

So you are saying the car will keep driving without 12V power? With no 12V battery or DC-DC converter functioning? So many critical things in the drivetrain including computers run on 12V.
 

ATPMSD

Active Member
Mar 12, 2021
1,317
1,203
Atlanta, GA
This is something I found and posted elsewhere:

Main battery powers:
HVAC,
Heater
Drive Units

12V powers the rest:
Lights
Audio
Screens
wipers
Powered brakes (without power, you can still mechanically brake but harder)
Powered steering (without power, you can still mechanically steer but harder)
Battery Management System (no 12V means no way to charge the main battery)
Small motors/solenoids/electronic latches: for seats, windows, doors...
Accessories...
 

ShawnA

Active Member
Supporting Member
Nov 13, 2017
1,105
864
Edwardsburg, MI
Hi @UShe ,

I would check your low voltage levels.
All of your readings are consistent with a 12 volt lead acid battery...
The "12 Volt" AGM batteries are slightly lower voltage...

From the Model S and Model X forums where people are trying
to connect radar detectors and other accessories - They are cautioning
to be mindful that the new lithium ion low voltage battery runs close to 15.8-16 Volts...
This can and will ruin some accessories.

Unless you can get or build a different power supply to supply nearly 16 Volts
you are likely to always be too low on the lithium low voltage battery voltage.

Good luck,

Shawn
 
He
Hi All,

The car had a rear end damage (R Bumper, Liftgate):

1. Pyro fuse was blown: Have replaced
2. Driver side Seat belt restraint stuck: Not yet repaired/replaced
3. All Airbags are good

  • After the Pyro fuse was replaced, the charge port light has turned from Red to Blue but the car still won't charge. Occasionally I am able to click on the screen to “Start Charging”. The button momentarily turns gray (unclickable) but doesn’t charge and then the button returns to active but not clickable anymore. The car shows maintaining 260 miles of charge
  • The 12v battery drains and dies in few minutes with these messages. I also got a new 12v Li-Ion battery from Tesla and that too died shortly. Now I am using an external Lead Acid.
    • VCFRONT_a478 Schedule Service – Vehicle may not restart
    • VCFRONT_a402 Electrical system backup power is unavailable - Vehicle will consume more energy while idle
    • VCFRONT_a192 Electrical system is unable to support all features – shutting down features to conserve energy
    • VCFRONT_a191 Electrical system power reduced - Vehicle shutting down
  • On connecting the 12v battery, I can hear the usual low sounds and the screen turns on. I can put the car in “Transport Mode” and the EPB works fine.
  • But I do not hear the High Voltage Battery contactors closing sound and this is the likely the problem (and so the message VCFRONT_a402 Electrical system backup power is unavailable)
Trying to figure out. Didn't find any shorts or severed wires (except for the parking sensor harness on the Rear bumper which has been disconnected).

Appreciate any Help.
Hi

Did you find what is the problem, I have also same thing :(
 
Okay, so this is what I learnt:

Pin 5 on the battery is a LIN pin communicating with the car. When the car (master) senses Low Power, it sends a SLEEP MODE COMMAND to the slave (12v Li-Ion battery) to go to a "Low-power mode operation" and disables the LIN Bus. The battery MCU is still operational and the LIN can receive commands but cannot send until a wake-up event. Due to this, the battery won't even charge (unlike Lead Acid) even if the the car is now running, or you have the charger connected or the HV battery is supplying power.

Two choices at this point:
1. Wake-up the battery LIN (which I haven't figured yet)
2. Buy a new 12v Li-Ion battery from Tesla (obviously it will have the LIN communicating) even though your battery isn't dead/bad. It's just on a low power protection mode.

I see two Potential Problems:
1. Similar to my case, in an accident, the Pyro fuse will blow and HV battery will disconnect. The 12v Li-Ion will last you 30 minutes and then go to sleep unless you disconnect it. I saw that the car does warn how much power is left on the 12v until 5% remaining and then shuts off.

2. For any reason (maintenance or so) you disconnect the HV First Responders' Loop but leave the 12v connected, you should watch the car's screen and not let the 12v go to sleep.

I have a Model Y from Dec 2021 that has a 12v Lead Acid. The car in the above reference is a Model Y from Jan 2022 and has this new 12v Li-Ion. So I am assuming all Model Ys after Jan 2022 may have the Li-Ion 12v.

Thought I should share. Hope this helps some one..
Did you manage to wake up the Li-on battery?
I got similar problem with my M3 12v li-on battery. While I could connnect external lead battery to wake the car up but the li-on battery not charging at all and after leaving the lead battery connected for 30mins then disconnected, the voltage of li-on is barely 1v
 

ATPMSD

Active Member
Mar 12, 2021
1,317
1,203
Atlanta, GA
Is there a section or forum dedicated to servicing out of warranty Teslas in a DIY setting as well as like this salvaged vehicle with issues?

Curious to know what is possible to diagnose and repair in a DIY setting.
For repair, a good start is get the service manual, which is now free


Look under service subscriptions
 
For repair, a good start is get the service manual, which is now free


Look under service subscriptions
Yes I have gone through that.

What I am searching for explicitly is discussions and documentation of the hardware in these cars when they fail, symptoms leading to the failures and what specifically have people found to have failed and possibly fixed and repaired with understanding and discussions of plausible reasoning for failure with accessible tooling and capabilities in regards to the EV specific systems.

I don't see much chatter about people digging into these fixing and solving small EV specific and Tesla specific problems that are popping up very often with these. Knowing most are new/newer vehicles and seemingly fairly reliable for a younger manufacture, there are still problems and failures out there, but I am not finding many documented cases in all the different places I have been looking.

The few things I have seen are component teardowns from Ingineerix and a few youtube channels repairing salvaged vehicles.
 

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