2008 Prius – Low Power on Highway & Uphill, Loud Engine, P1121 Code, Throttle Already Replaced

how many miles/km on her?

 

Are you beyond the weight limit of the car while your going up hill? The weight limit is in the drivers door jam. The car really doesn't carry much weight - 4 adults and it's near or over capacity. Stomping harder on the gas pedal going uphill isn't going to make the car go any faster uphill - the eCVT transaxle is trying to determine the correct gearing. All you'll accomplish is blowing up the engine by over-reeving it.
Something could be choking-off your engine and ECU is probably engaging safeties. Check the exhaust pipe for clogs, the CAT internal honeycombs can fall apart when a car is abused like that.

1. There probably isn't a throttle body issue, since it runs fine on the flats. Fix the flow control valve issue - may cause engine overheat.
2. Take a picture or write down the error codes BEFORE erasing them. Check cooling fan operations.
3. Install an engine coolant temperature gauge and ease off the engine when it hits 102C; normal operating temperature is 85C-100C; Higher temperature operations will eventually cause major engine damage.
4. Change the ATF in the transaxle, if that hasn't been done.
5. That 4-year old battery, was that a new OEM battery or rebuilt. If it's a rebuilt that could be your problem. Also make sure the battery cooling fans are working properly. I know it gets really hot in Jordan.
6. Check the MAP sensor on the air intake, that also provides barometric pressure readings so the ECU can adjust mixture based on the thinner air at altitude.

That's all I got, until you can get us error codes and mileage of the car.

 

It's often a disaster when people mix-n-match meanings for manufacturer-defined trouble codes like that.

All P1 codes are manufacturer-defined: different manufacturers can use the same code in the P1 range to mean completely different, unrelated things.

P1121 in a gen 2 Toyota Prius means coolant flow control valve position sensor circuit stuck, period, end of sentence. The code has nothing to do with any throttle anything.

Somewhere else in the world, there is some other model of car where P1121 has something to do with a throttle/pedal position sensor. When somebody working on a Prius happens to see that in some generic listing of codes somewhere, that's a pure distraction at best, and that's when it doesn't lead to spending actual money doing stuff with the throttle or pedal.

I wish there were a way we could warn people about stuff like that more prominently.

 

Thinking is NOT the same as knowing !! It's the little things that will give you clues to the actual problem and the throttle body is nowhere near to the MAP sensor. You need a good, smart mechanic to work on these cars - NOT so smart ones will just throw parts at a problem hoping to fix it. By the way; P1121 on a gen2 Prius is the coolant control valve - coolant temperature is one of the critical things the ECU looks at to determine gas mixture - so dismissing it out of hand isn't going to fix your problem !!! Go back to the beginning of this paragraph; CLUES to your actual problem.........

Good Luck.....

 

Wait a sec ... does a gen 2 even have a MAP sensor?

 

Not sure, but something is reporting to the ECU barometric pressure to compensate for thinner air at altitude. If there isn't one, the upstream O2 sensor would have to do that job.

 

I don't think it needs that separate reading. The MAF sensor (which it definitely has), being a mass airflow sensor, is already telling the ECM the true mass of air being taken in, regardless of altitude or density.

Gen 3 also has a MAP (manifold absolute pressure) sensor, but uses that to confirm things like EGR flow, which isn't a thing for gen 2. FWIW, in gen 3, which has the MAP sensor, it really is right next to the throttle body.

 

No, it does not have one of those.

 

IMHO; the problem isn't here nor there - it's partially the car and partially the OP.
Those old Prius don't climb very well to begin with - not enough horsepower for long climbs. It's basically comparable to an old air-cooled VW bug, but the VW has an advantage - stick shift. They both get really hot and mushy on a long climb, Prius will move until the traction battery is depleted. Had the same issue with my old Prius C; the last leg of the climb into south lake Tahoe - creeping along like an air cooled VW bug because the traction pack is fully drained. That pack gets fully charged by the time I reach lake level; but if you put your hands on the lower rear passenger seat panel, you can feel the heat radiating off that traction pack. Makes a great hand warmer in the winter months.
My gen4 Prime will actually make the entire climb, though I'm conserving electrons everywhere I can, because of my history with the Prius C

 

All the other maintenance are done? Like spark plugs. Engine struggling and no power.. i think if you keep driving like this, it may kill some part inside. Fix the coolant pump error asap.

Prius only have MAF sensor right ? not MAP sensor. You can check the value from this using a scanner and compare with known values at certain rpm. But if it is too bad, it should throw an error code.

 

I've seen many that don't throw codes because they're just on the edge of tolerances. Ditto with upstream O2 sensors, usually get a complaint that the car is now burning more gas and has lost a few mpg - but the power is back. Dammed if you do or dammed if you don't; I do warn them that's going to happen but it usually falls on deaf ears. I toss the old one in their wheel well and ask them if they want the old one put back in. A couple actually wanted me to do that.....

 

I think better idea would be to check the fuel trims first and go from there. Then check the MAF readings at various RPMS.

One of my friend went almost 150k on his odyssey with original spark plugs which were due at 105k. Finally it started misfiring at random and found that it was cracking and about to break off.

It seems the tolerance percentage on Toyota / Honda is higher than German cars like VW/BMW . They programmed it like that so that you will be forced to replace it earlier. Don't if it is good or bad idea. Some where i read that for O2, Honda uses like 20 0r 25% where as BMW is only 10%. Could be wrong.