Error code P0121 brake override malfunction solved in the field (1 Viewer)

[FrazzledHunter]

We were out camping this past weekend and I managed to run my starter battery flat.
Anyway, we were packing up to leave camp Sunday night and I noticed the dome light was dark.
Hmmm...so putting the foot on the brake and pressing start...nothing; not even a clicking sound.
No problem! I jumper to the 2nd battery and the LC starts up fine.

After the nav screen reboots I get a warning on the dash:
"Brake Override Malfunction" "Reduced Engine Power" "Visit the Dealer" or something like that.
So I stopped & started it a few more times.
Same outcome.
I floored the accelerator, all it would do is go to about 1800 RPM and the engine sounded rough, very rough.

I put into D and heard a "thunk" and rolled a bit forward.
Put it into R and heard a "thunk" and rolled a bit backward.
Did that a few times.

My wife asks: "So is something wrong with the truck?"
Me: "Ummm we're not going anywhere I don't think"
Discussion ensued...

So I get on the web (luckily we had internet) and found this website which ultimately saved the day:
How To Reset Brake Override Malfunction Toyota - CarInfoGuide - https://www.carinfoguide.com/how-to-reset-brake-override-malfunction-toyota/

• Step 1: Turn off the Engine
  • The first step is to turn off the engine. This will ensure that the system is completely reset and ready to be restarted.
• Step 2: Press and Hold the Brake Pedal
  • Next, press and hold the brake pedal for at least 5 seconds. This will help to discharge any residual energy in the system.
• Step 3: Start the Engine
  • After holding the brake pedal for 5 seconds, start the engine. This will reset the brake override system and should resolve any malfunctions.

I had to do the above 2 times and the system was cured.
The engine would rev to 5000 rpm and it sounded great.

While that seemed to cure the problem there was still a check engine light on.
I carry the Blue Driver dongle & app and connected the dongle, scanned for codes, and found Confirmed, Pending and 1 Permanent code.

The codes were P0121 "Throttle/Pedal Position Sensor/Switch "A" Circuit Range/Performance"
I cleared all the codes, the Check Engine Light went out, re-scanned and all was clear.
We drove home with no problems. The truck appears fine now.

I'll keep an eye on this as there may be something wrong.

I am assuming that the dead battery was the root cause of all this because the truck has been running fine.
It seems to me that if you lose your battery these vehicles can get seriously jacked up.

I hope this helps someone.

EDIT here's the diagnostic codes from Blue Driver:

 

[bloc]

Good tech, thanks for posting.

 

[FrazzledHunter]

A bit of new info…

I thought I’d follow up with mentioning I replaced the Trustart battery yesterday with a Deka 727FMF. I mentioned the error code problem I had Labor Day weekend so I asked the guy doing the swap if he could PLEASE keep power on the system so there would be no chance of a repeat. He declined for safety reasons.

Soooo I gulped and said to go ahead. The system came up fine after rebooting! So far so good!!! I started it whereupon it immediately stopped. I restarted again, it kept running and all was well – no codes no problems. I asked about the initial stop. He claimed that this was normal for Toyota and “Toyota did that on purpose for safety reasons”. He changes batteries all day so I assume he knows better. They sold & installed my 2nd battery and I really like/trust the family running this business. I never heard of this but thought I’d pass it along.

I was just relieved the truck didn’t act like it did Labor Day weekend and that I didn’t have to have it towed.

BTW, I mentioned my experience with the charger* and he guessed the battery was shorted and said it’s the charger putting out too much charging current due to the battery being shorted. That exactly matched what I heard in here – thanks to all!

*EDIT: I put the battery on a charger after we got home and heard a hissing & popping.
REF:
SQOD Squad - Stupid Question Of the Day - https://forum.ih8mud.com/threads/sqod-squad-stupid-question-of-the-day.862977/page-289#post-15138680

But…does this stopping after initial start following a battery change sound right?

 

[sdnative]

But…does this stopping after initial start following a battery change sound right?

Yes normal. Mine does that as well after disconnecting the battery for some time. The engine will initially start right up then fade out quickly and die. Second time it starts right up and stays running.

 

[FrazzledHunter]

Yes normal. Mine does that as well after disconnecting the battery for some time. The engine will initially start right up then fade out quickly and die. Second time it starts right up and stays running.

THANK YOU! I wasn't sure if there wasn't still a lurking problem; I'm a bit skittish after our experience of almost getting stranded in the woods. Still no idea why that error code happened. The battery tech had no idea as to why the P0121 code presented earlier.

 

[bloc]

I vaguely remember reading the way to avoid the start/stall after power loss is to leave the ignition on for a couple minutes before starting. I suspect it is caused by some elements of the system still booting or something along those lines.

Since reading that, the last time I disconnected the battery I tried it and no stall. So maybe give that a shot.

 

[TeCKis300]

A bit of new info…

I thought I’d follow up with mentioning I replaced the Trustart battery yesterday with a Deka 727FMF. I mentioned the error code problem I had Labor Day weekend so I asked the guy doing the swap if he could PLEASE keep power on the system so there would be no chance of a repeat. He declined for safety reasons.

Soooo I gulped and said to go ahead. The system came up fine after rebooting! So far so good!!! I started it whereupon it immediately stopped. I restarted again, it kept running and all was well – no codes no problems. I asked about the initial stop. He claimed that this was normal for Toyota and “Toyota did that on purpose for safety reasons”. He changes batteries all day so I assume he knows better. They sold & installed my 2nd battery and I really like/trust the family running this business. I never heard of this but thought I’d pass it along.

I was just relieved the truck didn’t act like it did Labor Day weekend and that I didn’t have to have it towed.

BTW, I mentioned my experience with the charger* and he guessed the battery was shorted and said it’s the charger putting out too much charging current due to the battery being shorted. That exactly matched what I heard in here – thanks to all!

*EDIT: I put the battery on a charger after we got home and heard a hissing & popping.
REF:
SQOD Squad - Stupid Question Of the Day - https://forum.ih8mud.com/threads/sqod-squad-stupid-question-of-the-day.862977/page-289#post-15138680

But…does this stopping after initial start following a battery change sound right?

Agreed that the initial start stall is normal.

Any error codes with a battery issue is not worth chasing... all sorts of weird things can come up with electronics not getting enough juice.

It's not likely the jumper shorted the battery as they don't have voltages higher than system voltage. What's more likely is the battery has been degrading over time, sulfating, building up lead crystals that drop and short plates. Higher end batteries have more lead in their plates and deeper cell pockets to handle wear.

 

[TeCKis300]

I vaguely remember reading the way to avoid the start/stall after power loss is to leave the ignition on for a couple minutes before starting. I suspect it is caused by some elements of the system still booting or something along those lines.

Since reading that, the last time I disconnected the battery I tried it and no stall. So maybe give that a shot.

Yes, this works

 

[kcjaz]

Yes, this works

So my 2013 has always stalled on the first start after the battery being disconnected. My newly purchased 2015 does not do that. I had the battery disconnected for more than 24 hours as I removed the OEM head unit and transplanted my Tesla HU from the 2013 to the 2015. The 2015 fired right up and didn’t stall.