Multiple alerts- truck in limp mode-Resolved (for now)

[JCERRN]

Got in the truck and it threw multiple errors- will list below, but vehicle in limp mode. Tried getting out and back in as recommended, issues persist. Roadside cant do remote diagnostics, only initiate tow to SC. SC closed until monday, so thats my only option right now.

no idea what the source is- but it seems like multiple controllers went offline and are not communicating with the truck. Already had my PCS replaced once.

had a reduced charging issue a couple weeks ago, SC said it was not a repeat PCS failure because it only happened once. Wonder if that was the warning shot. Who knows.

Errors:
TAS_a313_dampingCntrlDisabled
DI_a062_systemLimpMode
RSA_a211_activeRampingZero
DI_a127_pepsMIA

Power reduced
Loss of system redundancy detected- unable to shift out of park. Out of Park (P), the vehicle may suddenly lose electrical power, steering, and propulsion, and may be unable to apply the parking brake.

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[RustyEdges]

That's a real bummer . I hope you are able to get back home.

 

[TexasDev]

What year CT and when did you get the PCS replaced? (any idea if it was rev-G?)

 

[JCERRN]

What year CT and when did you get the PCS replaced? (any idea if it was rev-G?)

2025, replaced april 2025 with rev E

 

[JCERRN]

That's a real bummer . I hope you are able to get back home.

Ty. Fortunately, the issue happened at home and i had alternate transportation to get where i needed to go.

 

[TexasDev]

2025, replaced april 2025 with rev E

Dang. Well here's to hoping rev G solves it for you permanently.

 

[JCERRN]

Dang. Well here's to hoping rev G solves it for you permanently.

Not even sure thats the issue, but the LLMs seem to think its likely the pcs or some related connector, since they are all on the 48v system, and those all going offline or into protective mode indicates either they lost power, there was a spike in power, or failed, or each of those things simultaneously failed, which is highly unlikely. Its been fine for about 5000 miles (vehicle just hit 10k miles…)

 

[mongo]

Not even sure thats the issue, but the LLMs seem to think its likely the pcs or some related connector, since they are all on the 48v system, and those all going offline or into protective mode indicates either they lost power, there was a spike in power, or failed, or each of those things simultaneously failed, which is highly unlikely. Its been fine for about 5000 miles (vehicle just hit 10k miles…)

Looks like wire harness or connector fault. Drive unit can't talk to the primary steering motor: DI_a127_pepsMIA

 

[JCERRN]

Looks like wire harness or connector fault. Drive unit can't talk to the primary steering motor: DI_a127_pepsMIA

in service mode, it says one or more messages from the PEPS (primary electronic steering ECU is not being received on the CAN. Looks like this is triggering rear steering actuator to be upset and disable rear steer. The suspension damping is also upset because it is detecting multiple missing CAN inputs so it is putting itself into failsafe mode, and this is all resulting in the vehicle drive interface or drive inverter going into limp mode.

 

[RoboTaxi]

the truck is going to suck out of warranty.

 

[JCERRN]

Alright, so i finally had a chance to sit in the truck and logic through the errors. As @mongo said, the DI (driver interface) is putting the truck in limp mode (red screen of death) because the Primary Electronic Power Steering (PEPS) ECU isnt being read on the CAN for some reason. The other errors are failsafes because of this. The PCS is green, no issues detected there.

The steering still works, the secondary steering pathway is still functional, but because of how conservative the truck is, because the primary system is down, it is freaking out and going into limp mode.

i have no idea why the PEPS is malfunctioning but it could be either a harness/connector issue (either 48v power or network), the unit failed, or it has somehow crashed its software.

Will see what service says, but because i dont know why the peps is malfunctioning, i think i still will have it towed to the SC

The steering still works, the secondary steering pathway is still functional, but because of how conservative the truck is, because the primary system is down, it is freaking out and going into limp mode.

 

[mongo]

Alright, so i finally had a chance to sit in the truck and logic through the errors. As @mongo said, the DI (driver interface) is putting the truck in limp mode (red screen of death) because the Primary Electronic Power Steering (PEPS) ECU isnt being read on the CAN for some reason. The other errors are failsafes because of this. The PCS is green, no issues detected there.

The steering still works, the secondary steering pathway is still functional, but because of how conservative the truck is, because the primary system is down, it is freaking out and going into limp mode.

i have no idea why the PEPS is malfunctioning but it could be either a harness/connector issue (either 48v power or network), the unit failed, or it has somehow crashed its software.

Will see what service says, but because i dont know why the peps is malfunctioning, i think i still will have it towed to the SC

The steering still works, the secondary steering pathway is still functional, but because of how conservative the truck is, because the primary system is down, it is freaking out and going into limp mode.

It seems weird that only the drive inverter is saying PEPS is MIA. PEPS talks directly to left controller and to the Steering Feedback Actuator (SFA) which itself talks to the left controller.

Did you update software recently?
Have you tried dual scroll wheel reset and Power Off?
Could also try a full power disconnect, but that's more hands on, as is software re-deploy.

had a reduced charging issue a couple weeks ago, SC said it was not a repeat PCS failure because it only happened once.

Any chance that event is still in the alert log?

 

[JCERRN]

It seems weird that only the drive inverter is saying PEPS is MIA. PEPS talks directly to left controller and to the Steering Feedback Actuator (SFA) which itself talks to the left controller.

Did you update software recently?
Have you tried dual scroll wheel reset and Power Off?
Could also try a full power disconnect, but that's more hands on, as is software re-deploy.


Any chance that event is still in the alert log?

Tried two wheel, full sleep/wake (multiple times)

Software updated to 2026.2.9.1 a few days ago.

Unless there is a deeper log, my even log seems to only go back a few days (ive got a few reoccurring alerts that take up most of the log thats visible to me…) those were documented by service but were last month.

I agree that its weird the PEPS is randomly not working as every other component of the steering system is operational. Im leaning more toward software glitch than anything.

i have a service appointment this week anyway, was supposed to be friday but ill have it towed there tomorrow rather than dig into it myself (good ol warranty)

 

[syburtruck]

On the early Model S Plaid that I owned way back when, this happened due to one of the modules on the bus initializing late. Once that happens it needs a deep power cycle (or reset) before it will retry -- usually because there's a root cause lurking.

On the Plaid S, the early units had a service campaign that involved installing a second working harness and some software to make sure the system woke up. (In my case it was one of the modules for the adaptive suspension.)

Doubt that's the same cause here, you might be able to find a way to get it to work but service action is definitely required. (Realize I am stating the obvious...)

 

[JCERRN]

On the early Model S Plaid that I owned way back when, this happened due to one of the modules on the bus initializing late. Once that happens it needs a deep power cycle (or reset) before it will retry -- usually because there's a root cause lurking.

On the Plaid S, the early units had a service campaign that involved installing a second working harness and some software to make sure the system woke up. (In my case it was one of the modules for the adaptive suspension.)

Doubt that's the same cause here, you might be able to find a way to get it to work but service action is definitely required. (Realize I am stating the obvious...)

thanks for the input. No idea why the PEPS ECU decided to [x] itself from the conversation. I dont really want to pay for SM+ until im out of warranty lol. ill see what SC says. Hopefully they will have a loaner for me tomorrow when i show up….

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