What to make of this? Tesla Service says it’s not PCS.

[Uzi05]

In April, I took my car into service because my car for a long time would not charge at 48 amps, I would have to drop it down to 40 amps to stay there or else it would drop down to 24 amps. I confirmed it wasn’t a wall connector issue.

They replaced some part and that didn’t help the charging stay at 48 amps. Then they made another appointment saying it’s most likely the HV battery. Then, within 2 weeks, my home charging limited to 24 amps with PCS warnings and then eventually no AC charging at all.

They confirmed in messages that they will need to replace the HV and PCS on May 12th with an appointment for 7/6.

When I came to drop my Cybertruck, they insisted that only the HV battery is needing to be replaced. I stressed to them that I’m certain I have the PCS issue that every Cybertruck is having right now. But they are saying they’re sure it’s just HV battery and my truck does not have PCS issue.

Luckily, I have a loaner now because only supercharging when the closest ones are 30 minutes away has been a huge pain.

I’m just disheartened and venting at this point. Why are they not just fixing the PCS? I see everyone else getting there’s done. I clearly have the same issue.

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[LarryASilva]

For what it is worth ... I decided to run your interesting question past Gemini AI. The answer sheds a lot of light on your question.


MY QUESTION:
As all AI engines know, the PCS issue with the Cybertruck is well known. What would cause Tesla to report that both the HV battery and the PCS need to be replaced?

GEMINI AI ANSWERS:

When Tesla recommends replacing both the Power Conversion System (PCS) and the high-voltage (HV) battery in a Cybertruck, it is almost always due to electrical contamination, physical damage at the connection points, or a cascade failure that threatens the integrity of the battery pack.

While the PCS and the HV battery are distinct components, they are physically and electrically "tethered" in ways that make their failure modes interrelated. Here is why both are often replaced together:

1. Thermal and Electrical "Blowback"
The PCS is responsible for converting AC power (from home charging) to DC, and for stepping down high-voltage power to run the truck’s 48V systems. If the PCS suffers a critical internal failure—such as a short circuit or a massive spike in current due to a component failure like a MOSFET—that electrical surge can travel back through the connections into the HV battery’s internal circuitry. To protect the vehicle, Tesla’s diagnostics may determine that the battery’s sensitive management hardware or contactors have been compromised by the same surge that killed the PCS.
2. Contamination or "Fretting" Damage
The connection between the PCS and the HV battery is a critical, high-load interface. If there is a poor connection, moisture ingress, or corrosion at the high-voltage busbar interface:

• Localized Melting: Excessive electrical resistance can cause intense heat, leading to melting or "fretting" of the connectors on both the PCS side and the battery pack's high-voltage terminal.
• Terminal Damage: Once these high-voltage terminals are physically damaged or pitted by electrical arcing, they cannot be reliably cleaned or "re-pinned." Because the battery's terminal is often integrated into the pack assembly, the entire battery pack must be replaced to ensure a safe, factory-sealed connection.

3. Coolant Contamination
The PCS and the HV battery share cooling loops. If the PCS suffers a failure that results in an internal coolant leak, that liquid can be forced into the high-voltage harness or even the battery pack itself. High-voltage systems and liquid coolant are extremely dangerous in combination; if coolant has entered the battery enclosure, the pack is typically deemed non-serviceable and must be replaced to prevent future short-circuiting or fire risks.
4. Diagnostic "Safe-State" Protocols
Tesla’s diagnostic software is exceptionally conservative regarding high-voltage safety. If the system detects "insulation resistance" faults (where the high-voltage system is leaking current to the chassis) that the technicians cannot isolate to just the PCS, they will often require a full system replacement. Replacing both components ensures that the "new" PCS is being mated to a "pristine" battery environment, eliminating the risk of a latent fault in the old battery damaging the new, expensive PCS unit.
Summary of the "PCS Issue"
It is worth noting that many PCS failures are currently being attributed to internal component defects (often related to power electronics) rather than battery issues. However, if you are being told both need replacement, it is almost certainly because the service center has detected physical damage at the junction between the two or contamination that makes it unsafe to reuse the existing battery terminals.
If your vehicle is still within the warranty period—particularly under the newer 7-year/70,000-mile ZEV powertrain warranties—ensure you clarify with the service advisor whether this is being covered as a defective component repair or if they are citing external factors (like environmental damage or debris) for the dual-replacement.

MY QUESTION:
But ... would the 4680 cells themselves be harmed?

GEMINI ANSWERS:
The short answer is no, a PCS failure does not typically "harm" the 4680 battery cells themselves in the way you might fear—such as causing them to lose capacity or degrade chemically.
The cells and the PCS are distinct components. The PCS is a power electronics module (the "brain" that manages charging and voltage conversion), while the battery pack is a storage vessel for energy.
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However, when a technician tells you that both need to be replaced, it is almost never because the cells are bad. It is because the "battery pack" is being treated as a single sealed, proprietary assembly that cannot be repaired at the component level.
Here is why that replacement recommendation happens, even when the cells are likely perfectly fine:
1. The "Non-Serviceable" Architecture
Tesla designs its battery packs to be essentially sealed "black boxes." When an electrical fault occurs at the junction between the PCS and the battery (like a short circuit or a fried contactor), the damage usually occurs at the high-voltage busbars, connectors, or internal safety fuses located inside the battery pack casing.

• Tesla’s service centers are generally not equipped to open a 4680 pack to replace a single connector, a melted busbar, or a blown fuse.
• If the connection point on the battery side is damaged (e.g., pitted from an electrical arc or melted from a short), the entire pack is deemed "compromised" and replaced to maintain factory safety standards.

2. The Difference Between "Cells" and "Pack"
It is important to distinguish between the individual 4680 cells and the entire battery pack assembly:

• The Cells: These are the thousands of tiny cylinders that hold the chemical energy. They are extremely durable and are not affected by the PCS's failure to convert AC power.
• The Pack: This includes the cooling system, the management electronics (BMS), the high-voltage contactors, and the massive internal wiring harness.
• When you hear "replace the battery," it is usually because the infrastructure inside the pack—not the chemistry of the cells—was damaged by the electrical event.

3. Why the "Both" Requirement?
You might wonder why they can't just fix the PCS. If the PCS failure caused an "overcurrent" event or a short circuit that traveled into the battery, Tesla’s diagnostic logs will show a "permanent fault" or "insulation resistance" error.

• Because the battery's internal safety components (the contactors/fuses) are designed to "trip" only once in a catastrophic event, they cannot be reset.
• If the PCS is replaced but the battery's internal safety components are also blown or damaged, the new PCS would fail immediately upon connection. Replacing both is the only way to ensure the vehicle is "electrically clean" and safe to drive.

In summary: Your 4680 cells are likely still perfectly healthy, but they are trapped inside a housing that has sustained damage to its electrical interface. Tesla’s "replace both" protocol is a safety and liability measure to ensure no residual electrical damage causes a fire or a secondary failure down the road.

 

[mongo]

In April, I took my car into service because my car for a long time would not charge at 48 amps, I would have to drop it down to 40 amps to stay there or else it would drop down to 24 amps. I confirmed it wasn’t a wall connector issue.

They replaced some part and that didn’t help the charging stay at 48 amps. Then they made another appointment saying it’s most likely the HV battery. Then, within 2 weeks, my home charging limited to 24 amps with PCS warnings and then eventually no AC charging at all.

They confirmed in messages that they will need to replace the HV and PCS on May 12th with an appointment for 7/6.

When I came to drop my Cybertruck, they insisted that only the HV battery is needing to be replaced. I stressed to them that I’m certain I have the PCS issue that every Cybertruck is having right now. But they are saying they’re sure it’s just HV battery and my truck does not have PCS issue.

Luckily, I have a loaner now because only supercharging when the closest ones are 30 minutes away has been a huge pain.

I’m just disheartened and venting at this point. Why are they not just fixing the PCS? I see everyone else getting there’s done. I clearly have the same issue.

If service mode doesn't have the cyclo health alerts, it not the PCS. 40A charging is a different failure than the DCAC sub-module fault.
They should verify AC charging before returning the truck.

 

[Uzi05]

If service mode doesn't have the cyclo health alerts, it not the PCS. 40A charging is a different failure than the DCAC sub-module fault.
They should verify AC charging before returning the truck.

I do have the PCS warnings. Still they insisted now my truck doesn’t have the PCS problem

 

[mongo]

I do have the PCS warnings. Still they insisted now my truck doesn’t have the PCS problem

The HVBATT errors could be causing the displayed PCS charging fault (whereas PCS wouldn't cause that HVBATT fault). The key indication for PCS based charging failure are the DCAC health faults in service mode.

 

[mongo]

On the other hand

If it is, they'll replace it too

 

[Uzi05]

The HVBATT errors could be causing the displayed PCS charging fault (whereas PCS wouldn't cause that HVBATT fault). The key indication for PCS based charging failure are the DCAC health faults in service mode.

Wow, thank you for the reassurance sir. I hope I do get AC charging back at full 48A after the HV battery replacement. They said it’ll be about a week.

 

[mongo]

Wow, thank you for the reassurance sir. I hope I do get AC charging back at full 48A after the HV battery replacement. They said it’ll be about a week.

Oh my little grey cells just reminded me that a pack swap includes the PCS (along with everything in the Ancillary Bay)

 

[Outdoors]

Oh my little grey cells just reminded me that a pack swap includes the PCS (along with everything in the Ancillary Bay)

Yes, and when I asked in March when my pack was replaced if I would have any new PCS problems. Tesla said no. As I got a new one.

Well the new PCS went .

 

[mongo]

Yes, and when I asked in March when my pack was replaced if I would have any new PCS problems. Tesla said no. As I got a new one.

Well the new PCS went .

That sucks

 

[Gigahorse]

Not the answer you want, but they don't have the PCS parts, big backlogs, so they are delaying/pushing those repairs back as far as possible.
They won't touch it until home charging is completely not working because the trucks will just sit at the service center for weeks/months waiting for PCS parts.

 

[bosshog]

I have one warning pcs a -051 Schedule service
I contacted service

SC sent me an update.
I haven’t had a problem since

Is this the early warning signs of failure?
What do I look for next ?

 

[agordon117]

I have one warning pcs a -051 Schedule service
I contacted service

SC sent me an update.
I haven’t had a problem since

Is this the early warning signs of failure?
What do I look for next ?

I showed an a051 several days before my home charging reduced to 24A and I got the a127 and a136 errors. I only saw the a051 in service mode though until the night before my charging speed was reduced. The morning the PCS went, I saw the a051 outside of service mode with "unable to charge, schedule service" in the notification screen.

So, your mileage may vary, but it does seem to be correlated from what I'm able to find and what I experienced.

 

[bosshog]

I showed an a051 several days before my home charging reduced to 24A and I got the a127 and a136 errors. I only saw the a051 in service mode though until the night before my charging speed was reduced. The morning the PCS went, I saw the a051 outside of service mode with "unable to charge, schedule service" in the notification screen.

So, your mileage may vary, but it does seem to be correlated from what I'm able to find and what I experienced.

So that code looks like the warning code before the other codes show up .

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