P1121 Code Which one is it ?

I worked on a Prius with both of these problems happening at the same time... Fix one of the problems and see what happens with the other.

 

So, ON A GEN2 PRIUS, a P1121 indicates a problem with the position signal on the coolant control (3 way) valve. (it's almost always a worn sensor in the valve- get a Toyota valve from a reputable source for the most reliable repair)

On any other make or car model, it certainly COULD be related to the TPS- but not here.
A "P0xx" is a generic powertrain code defined by the SAE- you (or a scantool) can look that up anywhere and get a correct meaning.

Any code that is "P1xx" is a powertrain code that is defined by the manufacturer. In this case Toyota decided to use it for the coolant valve. Ford or Chevy or Nissan might use it for TPS but that doesn't matter for your Prius. Your generic scantool doesn't have the correct code definitions for your Prius either.

Posted via the PriusChat mobile app.

 

On my spare 05 Prius, I just had to decipher the same thing. It's the coolant control valve assembly. I hope you don't have to spend a couple of HOURS getting the 10mm nut (on top) and 10mm bolt (on side) off the assembly bracket, like I did when mine were hopelessly rusted. The easy way at it is removing the driver's side headlight. Get a plastic bin/drawer low enough to slide under the car to catch the coolant, if you don't want to have to jack the car up like I had to. You might have to anyway, to get at the lower hose clamp. A long pair of needle nose pliers with 90 degree (or maybe 45 would work) bend makes quick work of sliding the hose clamps off onto the middle of the hoses.

When done, run the engine through at least 2 cycles of radiator fan on/off while adding coolant to the radiator cap you remove before the car warms up. The air will slowly burp out. When test driving it, get off the gas immediately if the red triangle of death comes on due to coolant temp. The car engine should run at 90C, the triangle comes on at 120C, and the temp can be going up really fast. I use a scan tool to watch coolant temp while driving, before and after doing anything with coolant.

 

^^^^ what he said.

 

Thanks for this...

I did indeed have an engine idle that was all over the map so in my case it was both throttle body control and the 3-way valve. But your point makes me wonder if a bad 3-way valve can have some kind of harmful thermal damage issue in the throttle body control sensor because there is coolant flow thru that device. Just not sure what happens to throttle body if coolant is not present?

Hmm... Wonder if @ChapmanF or @Elektroingenieur knows history of the association of throttle body sensor & 3-way coolant valve?

 

There is no association and there is no history. P1121 is a P1 code, which means it's a manufacturer-defined code, which means any car manufacturer can use P1121 to mean whatever they want in whatever car they want.

Toyota uses it to mean the coolant control valve in a Prius.

Some other manufacturer uses it to mean a throttle sensor in some other car. They can use it to mean whatever they want. That's all there is to it.

That's why when you're looking up trouble codes, especially ones that are in the manufacturer-defined ranges (see the chart in #5 above), just googling them isn't a good idea. You need to be sure you're finding what they mean for the specific car you're working on.

The same goes for trusting any code description that might happen to be built into your code reader.

The smart money always looks up the code in the car's repair manual.

Toyota Service Information and Where To Find It | PriusChat

 

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Here is the workup for DTC P1121 :

https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8CPDF%E6%A0%BC%E5%BC%8F/Prius%20Service%20Manuals%202004/%E4%BF%AE%E7%90%86%E6%89%8B%E5%86%8C/04pruisr/05/2054m/cip1121a.pdf

Here is the output for the search term "P1121" (from within Gen 2 Prius Care, Maintenance and Troubleshooting)

https://priuschat.com/search/104116549/?q=p1121&o=relevance&c[node]=12

FYI : you're moderated until you've posted 5 times.

 

On mine the nut was completely missing.

I don't know how it works if you don't completely drain the coolant like I did, but the easy way to handle the lower hose it to remove it at the other end. It's behind the fender liner and much, much easier to get at. If you loosen the inverter and prop it up there's just enough space to slide the valve and hose out through the top. Swap the hose over to the new valve and put everything back together. One of the videos I watched on YouTube suggested this and it made the whole process pretty easy.

I do have a long set of pliers with a 90 bend at the end, but after about two minutes of screwing around with that I decided to go the easy route.