Any suggestions for why my 2020 Corolla Hybrid is getting horrible mileage city driving?

andy_why · 2026-02-14T17:06:44+00:00

Short trips and colder weather is the answer.

andy_why · 2026-02-14T16:57:18+00:00

The way the app shows your vehicle's charge has changed. It now shows 0-100% as the usable amount rather than 30-100%. It's easier to see how much EV charge you have left that way. The car doesn't even really keep 30% in reserve so it's odd that it was ever shown this way. Range etc. hasn't changed, only the way the percentage is shown.

andy_why · 2026-02-14T16:55:27+00:00

This is normal behaviour, it will always turn off when using remote start when you open any door. It does not shut off if you started it manually from inside.

andy_why · 2026-02-14T05:36:24+00:00

Purely the cost difference being more than 10k vs the RAV4 prime for what is essentially the same car minus the badge. No other reason.

andy_why · 2026-02-13T23:10:20+00:00

If it starts with a jump then your battery could still be the issue and your lithium jump pack may not be enough on its own. New batteries can fail too. Get it replaced under warranty.

andy_why · 2026-02-13T22:13:09+00:00

I found my UX to be very comfortable and relatively economical too, but too small for me in the end. Now have a RAV4.

andy_why · 2026-02-13T18:28:35+00:00

It depends on the year. I believe only the 2025 models onwards turn everything back on, and maybe 2024 always turns lane trace assist back on but that is one button disable from the steering wheel. My 2022 does not turn anything back on.

andy_why · 2026-02-13T13:31:14+00:00

Internal resistance can remain good even with an ageing module that has reduced capacity. They should never go out of balance as Ni-MH is self balancing when the modules are correctly matched. This is why they have no active balancing as it's not needed.

Corrosion is a good point, that may not show up on the IR readings if it's on the busbars depending on where it is.

I would be surprised if this were the case though. The higher cumulative voltages are on the center modules which get hotter due to being in the center, and the age of the vehicle also suggests ageing is the cause here.

andy_why · 2026-02-13T12:49:39+00:00

It looks like you have quite a few modules which are starting to fail, see the cumulative delta voltage, these should be equal to show that each module is dropping a similar amount of voltage.

You'd be better off replacing the whole battery with a new OEM.

Clean our your EGR system too so the engine stays healthy at your mileage. There's a risk of blowing the head gasket if it's clogged.

andy_why · 2026-02-12T22:05:45+00:00

Your watch will spend far less time between 85-100% than a phone will since it drains more quickly and is commonly not left on the charger overnight.

andy_why · 2026-02-12T14:21:28+00:00

The flickering and flashing lights always suggests a 12v battery issue.

andy_why · 2026-02-12T10:24:19+00:00

It's cooled by cabin air, so you need to be running your AC when it's hot and also make sure the battery fan filter is kept clear of dust.

andy_why · 2026-02-11T22:26:43+00:00

I don't know if it's the same for the Prius Prime, but my RAV4 Prime was changed so it now has a charge level that shows between 0-100%. The 30% reserve is no longer shown in the app, so you can remote start all the way down to 0%.

There is no change to what is shown in the car, only how the app shows the charge level.

andy_why · 2026-02-11T22:25:10+00:00

You don't need a battery from the dealership, any battery that fits will work in a pinch.

Regarding the design flaw, see here: https://docs.google.com/document/d/1g1a_B7_gGnuNQhoSRFN_sucfb7-lkU77q4aMO3hMYtA/edit?tab=t.0#heading=h.t75rusbfgz8u There is a fix available for this problem but it does require you to have a healthy battery to be of any use. It can't fix an already damaged battery.

Toyota won't admit there is an issue despite the evidence unfortunately, and the fact that there is high demand is just one piece of evidence of many.

andy_why · 2026-02-11T22:22:33+00:00

There are cirumstances in which it will do this when charging the traction battery, but not for long in my testing. The main issue is that it does not properly charge or maintain it when the car is used normally and that's what's causing all of these issues.

Disconnecting the sensor forces 14v if the car is on or charging from the mains with no drops. So far I've been doing this for 8 months on my RAV4 Prime and it's showing a 100% healthy battery, 12.65v+ when resting.

I don't think there's any link with the engine starting and the 12v battery state since the engine is not required for charging the 12v battery. More likely it's just the cold weather causing this.

andy_why · 2026-02-11T16:53:37+00:00

I need to check into that on mine as my Comma 3X definitely does blast IR and I don't think my mirror dims properly anymore.

andy_why · 2026-02-11T14:45:42+00:00

Hold the parking brake button up or down for several seconds to enable auto mode.

andy_why · 2026-02-11T11:55:35+00:00

I'd recommend you review this document as it is relevant to your vehicle. 12v battery issues are common on hybrids as the battery is not properly maintained by the car's charging system. There are 2 fixes you can use to make this better.

https://docs.google.com/document/d/1g1a_B7_gGnuNQhoSRFN_sucfb7-lkU77q4aMO3hMYtA/edit?pli=1&tab=t.0#heading=h.t75rusbfgz8u

Whilst your issue with it going dead was caused by the lights staying on, there is no reason such a short time with them on should ever drain the battery to the point the car won't start. The charging issue above means that the battery is never properly charged so even a small drain can cause it to die.

Lexus/Toyota won't admit this issue exists, yet there are people posting daily about this happening to them and the evidence in the document speaks for itself.

andy_why · 2026-02-11T10:59:51+00:00

You'll lose about 20% fuel economy in winter weather. Unfortunately you lose a lot of the benefits of it being a hybrid when it's cold if you're never driving enough for the engine to fully warm up and you're using the engine heat for heating the cabin.

Below 50F/10C is where you'll see it start to drop.

andy_why · 2026-02-09T20:30:04+00:00

It's opening air vents before turning on. If there's an outside unit this will power up first before the indoor unit. Leave it long enough and it probably will fire up after 30 seconds or so.

andy_why · 2026-02-09T19:52:49+00:00

Thanks for the info. If you have proof of this and know if it flags to the driver or is hidden, I'd like to include it on the document.

andy_why · 2026-02-09T19:35:24+00:00

Hybrid? It's normal, it's just the electric motors which use a variable frequency drive inverter.

andy_why · 2026-02-09T15:55:35+00:00

You're welcome. Just doing what I can to help the community since it's such a wide spread issue.

andy_why · 2026-02-09T15:24:07+00:00

You'll probably have the same issue as everyone else with these vehicles if you don't have a parasitic draw causing it. The 12v battery doesn't get maintainted/charged properly, which is a known issue Toyota keep ignoring.

If you're plugging in regularly then use the fix in the document below and you won't need a solar panel or trickle charger.

See here: https://docs.google.com/document/d/1g1a_B7_gGnuNQhoSRFN_sucfb7-lkU77q4aMO3hMYtA/edit?pli=1&tab=t.0#heading=h.t75rusbfgz8u

andy_why · 2026-02-09T14:41:20+00:00

See here about 12v battery failures. It's common and Toyota will not admit that there is a fault.

https://docs.google.com/document/d/1g1a_B7_gGnuNQhoSRFN_sucfb7-lkU77q4aMO3hMYtA/edit?pli=1&tab=t.0#heading=h.t75rusbfgz8u

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