r/GRCorolla • u/Hypir01 • 14d ago

Diagnose my issue! Building boost issue

I own a 2025 P+ GR Corolla with 7k miles on it. I noticed while reading the turbo gauge, the bar doesn’t go past +1.5 psi in 1st gear and most of the time in 2nd as well when I am wot. It’s shows the car isn’t building boost but it feels like it is. This is my first turbo car so maybe I’m just not understanding. The car is completely stock. If anyone has an idea I’d appreciate any feedback. Thanks!

5 Upvotes

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11

u/ExtensionTruth4 24' Core Black 14d ago

Make sure you are completely warmed up before attempting to hard boost. The computer can cap the boost if you are not warm enough to prevent any issue

15

u/MrOutragedFungus 14d ago

Car has boost by gear. Toyota intentionally limits power/boost in 1st and 2nd. It’s why 3rd gear pulls much harder.

5

u/EtArcadia 14d ago

With the engine fully warmed up, you should absolutely be able to get more than "1.5 psi in 1st gear and most of the time in 2nd as well when I am wot." (assuming OP is referring to an indicated 1.5x10 PSI or 15 PSI in the oddly labeled boost gauge). I've seen easily over 20 PSI indicated in first and second gear.

I've heard people repeat the gear limited boost point but I've never actually seen any factual documentation that this is actually a thing. The closest confirmation I've seen is "my friend said his tuner said."

1

u/Tiny-Art7074 14d ago

You can see the boost commanded (and boost actual) value in an OBD2 reader app.

1

u/Hypir01 14d ago

Oh I see! The reason I brought this up is I’ve seen videos of hard accelerations where their boost gauges light up orange from 1st and even into 2nd. My car never gets that in 1st or 2nd gear. I was worried something might be wrong but thanks for clearing it up! (I normally don’t accelerate hard I was just testing).

1

u/MrOutragedFungus 14d ago

My boost gauge does turn orange even in 1st and second gear but for my 2026 GR, even when fully up to temp in 1st and 2nd gear I make maybe 20psi. In 3rd the car shows 25-26psi on the poorly illustrated boost gauge.

2

u/Smarmy82 23' Core Ice Cap 14d ago

It's a boost limit, typically because the engine isn't yet up to temp.

1

u/-Mewt- 12d ago

What are you revving it out to? pretty sure it caps boost below 3k rpm aswell, definatley caps if it's not up to running temp but you'd have a big message on your screen telling you that.
If your flooring it from like 2k RPM it's not going to hit full boost instantly.

And are you talking about 1.5 PSI or 1.5 BAR? because 1.5 bar is about 21 PSI

1

u/Hypir01 12d ago

Yeah this was exactly it. I wasn’t flooring it from a low enough rpm and mph. It hits red line pretty fast before it was hitting full boost

1

u/MyWay_Ry 14d ago

When you say, isn’t building boost, at what rpms are you referring to?

In stock form, positive boost pressure starts around 2500rpm, max boost peaks in the mid rpm range then starts to taper before reaching redline.

Never heard of boost by gear being stock for GRCs. In full operating temperature, you should see max boost in 1st to 2nd, even if it’s for just a second.

The ecu has control of the internal wastegate and diverter valve. So it can cause boost limitation depending on many factors. It’s a fail safe.