TRANSMISSION PROBLEMS (maybe)? help

Your Prius doesn't have a transmission in the conventional sense. It is not shifting gears, down shifting, or playing with clutch bands. All that is happening is that the computer tells the engine and MGs what to do. Unless you have a flaky problem with the ECU, everything is fine. Usually these things are nothing more than a panicked owner.

Do you have any warning lights?

Tom

 

The Prius has three "motors" for propulsion, as it were.

• There is the ICE, or Internal Combustion Engine. That's what you hear "running" usually (when it does run, which is not all of the time).
• Then there are two "motor/generators", so called because they can act as either electric motors or electrical generators. They are abbreviated "MG1" and "MG2"

The Prius uses a fairly complex assembly of different Control Units to manage all of its functions. I believe that ECU stands for "Electronic Control Unit".

Best wishes,

 

OP: Did you lose power going up the hill, or just notice the change in engine noise ?

 

In your position I would pull DTC codes. You can buy a scan gauge for about $150, or I think others have posted that auto stores will check for free. Call ahead to be sure. For now I would avoid pushing the car to it's limits. In fact I would baby it, if for no other reason than to be in a safer position if it acts up while driving.

Diagnoses will have to await the forum gurus. I find your description of the car revving without the throttle depressed the most interesting. Since the car did not lunge forward (right ?) it suggests the transaxle was in neutral, or very little load.

 

Did your battery SOC (State Of Charge) drop down into the purple range? That can happen with fast hill climbing, where the electric motor helps. Once the battery is drawn down, all of the power is coming from the engine, which is also trying to recharge the battery.

For long hill climbs, it is usually better to slow down a bit. Slow and steady will produce a faster overall climb.

Tom

 

First thing to check is that any floor mats you have aren't slipping under the pedals and catching on them. If you have the Toyota Prius mats (PRIUS stitched into the mat) they have a pair of holes in them on the rear edge, which hook over a couple of plastic hooks in the floor carpeting. Ensure the mat is properly hooked down so it can't move.

Could you confirm that you have a hatchback Prius, model code NHW20 with 'Hybrid Synergy Drive' badges? The older 'Classic' sedan sensed the throttle position differently.

The ECU detects the throttle position using magnetic Hall-effect sensors. There are two sensors which are supposed to change value in sync, and an error code should be logged if they're not doing so. A quick check to ensure that there isn't any metal or magnetic material stuck to the pedal, or in the vicinity, would seem appropriate.

My next explanation would be the throttle body motor, but again there's a position sensor that is supposed to confirm that the throttle is open at the requested angle and should cause a DTC to be logged and a Check Engine light.

The service manual says that for hesitation or surging, the Fuel Pump Control Circuit should be checked, then the injectors, then spark plugs.

 

I had the same thing happen to me last year going down to CA. I figured it was a batch of bad gas I got as my mileage was horrible from that tank. I would be interested to see if you find anything else out.

 

If you didn't get a 'check engine' light, there may not be a code BUT it is good to have it checked. First I'd like to list some hypothesis and then ask some other questions:

• battery limit - the symptoms are consistent with loss of battery charge. However, other things can limit the available traction battery power
• thermal issue - MG1, MG2, the inverter and the battery all have to stay within reasonable temperatures, generally under 100C. Before reporting an alarm the NHW20 may take protective actions to limit power without 'throwing an alarm.' The vehicle protects itself from permanent damage but may not through a 'check engine' or hybrid alarm that requires service.

But these are speculations and only by getting 'a code' or advanced instrumentation could you tell. Since it is a 2004, there may be a latent defect that protects the car without reporting an alarm. Now for a few questions to help understand:

• 2004 Prius - did you buy it new or used?
• hill - can you use Google map or Google earth to show the vehicle track when the problem first happened?
• speed control - your standard cruising speed is 80 mph? Foot or cruise control?
• transaxle oil - has it been changed yet? If you are taking the vehicle to a Toyota service center, please bring a clean, dry 8 oz. water bottle and ask for a sample of the used transaxle oil. ($40-120)
• coolant - has the engine and inverter coolant been changed? I understand there is a maximum life and yours might be at that point. ($50-150)
• throttle body and injector cleaning - has the throttle body been cleaned and/or fuel injectors? ($20-$60)
• spark plugs - have they been changed? At 100k miles, it is likely they are reaching the end of their design life and a change is in order ($60-100)
• engine air cleaner - what does it look like? ($15-50)

Understand that maintenance is not free but it is less expensive than the alternative. Many of these things you can do yourself, the lower cost, or you could have someone else do them, the higher. Of course prices vary by region and service center. Still, things to consider.

Bob Wilson