Engine revving high, transmission slipping - 1st gen Prius

Well, there's nothing inside a Prius transmission that can slip*, but there is something that can feel like slipping, when the car isn't able to use the normal amount of electric power in the mix, so the small gasoline engine has to rev unexpectedly high and supply the bulk of the power.

That can happen either because of a problem in the traction battery, or a problem in the power electronics (the "inverter", the silver box sitting above the transmission). Overheating of either one can cause the electric power to be protectively limited, too. Overheating of the inverter can be a symptom of an electric coolant pump that fails.

You want the trouble codes from the Hybrid Vehicle computer, which will tell you which of those things might be going on. If it gives you codes about the battery, then you also want the codes from the battery computer, which will be more specific.

None of the likely problems will turn out very hard to fix; the coolant pump is a small wad of cash, but not hard to swap, and if it's the battery, that's a larger wad of cash, but also not a hard job to swap.

Everything starts with knowing the trouble codes.

*ok, there is one thing that can slip, not really inside the tranny but between it and the engine, but it hardly ever does, and if it were, you'd be smelling hot-foundry smell like when people burn out their clutches or brakes.

 

Not overly optimistic, but lucky indeed

 

If it is as described, you should be good. You're going to want to get set up with an OBDII reader. The easiest is to buy a bluetooth device that plugs into the OBDII and then download one of the smartphone apps (Torque is popular). There's also an app called Dr Prius that will test the battery's health.

You should also confirm that the inverter coolant pump that Mr. Chapman refers to is working - your mileage is around the age when they fail, and it would burn up your inverter if you kept driving - although you should get all those Check Engine lights and the engine dying if it did. However, I wouldn't be surprised if it hadn't already been replaced, since they've replaced the battery.

The unit is bolted to the frame behind the driver's headlight. Small electric motor with two in/out fluid lines connected. The original has a black painted bracket and the newer ones have a bare metal bracket. With just the key on, you should be able to see the coolant circulating in the reservoir - it's the narrow rectangular reservoir back/center of the engine compartment, just left of the inverter and right of the brake fluid. You can also squeeze your hand down to it and feel it running and maybe hear it. Little bit of a PITA to replace because of the tight fit, but no special tools or skills required. Some talk about having to bleed the lines after replacing, but I've always pinched them off with vice grips to not lose fluid, and they work fine went I put the new one on. Part is about $130 online.

 

"overly optimistic" - not if the battery is as advertised. You can get the manufacturing date from numbers on the case, that'd tell you how old it really is, unless it's an old case that someone has used to rebuild with newer cells. The labels also vary - I'm not sure exactly how, but I think newer batteries have three big labels and the older ones just have one.

 

Like I said, just look and feel. You should get a CEL if it goes out, but it's so easy to monitor. There's write-ups here on replacing it. I just squeeze some vice grips on the incoming hose to close it off, then swap in the new one and I've not had to bleed it at all on the few I've done. The pain is getting to it - gotta take off the front bumper on that side (let it hang out of the way), and the headlight. Then getting the squeeze clamps off are a PITA, unless you have the special pliers. But it can be done.