2004 Prius Weak Engine

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Do you have any warning lights displayed on the dash?

Did you drive the vehicle around?

FYI : you're moderated until you reach five (5) posts?

 

I'm curious what you're using as a basis for judging weakness. Are you a normal driver of the car or is it pretty much GF only? Are you familiar with how the hybrid drivetrain runs/cycles the engine only when needed? If you're pressing the gas pedal while the car is just idling in the driveway, I don't understand how you can tell strong or weak. It will usually turn itself off after the warmup cycle. It will also idle down or shut itself off if the HV battery reaches a high state of charge, even if you have the gas pressed. The car is pretty smart. Maybe the car is just doing what it's supposed to be doing? The car should actually be a bit better with a new battery, as some old "death throe" 12v batteries will actually load down the 12v system slightly due to drawing larger than normal continuous charge.

 

The 12V auxiliary battery is not used to start the engine (ICE or Internal Combustion Engine), it is only used to boot up the computers and operate the lights, and other 12V devices. The ICE is started with the traction battery, so the 12V battery doesn't have to be large to start the engine. It's also supposed to be an AGM type battery, and I'm not sure the car is designed to keep a wet cell battery charged.

Regarding the engine not responding as you might expect when you push on the gas pedal, keep in mind that there is no direct connection between the pedal and the engine like traditional cars. The gas pedal just signals to the computers that you want to go faster and it makes the necessary adjustments to the ICE as well as the two motor-generators. The Prius is designed to drive like a conventional car, but it's not going to always react like one, especially if you're sitting in Park.