P0117 and now P1121 Prius 2004 2nd gen

Replace the 3 way coolant valve and the p1121 error will go away. DIY price is around $100 for the pump. I hope you didn't need to put much coolant into the radiator, as you'll most likely have to drain the coolant out to replace the pump.

 

delete

 

The p1121 doesn't affect much, maybe you'll not get cabin heat when you need it. You can drive around safely with that error. But your check engine light will remain on until it's fixed. This does not trigger the red triangle.

I'm unsure how safe it'll be driving with the p0117 error though. That is probably the cause of master warning light (red triangle).

 

You may want to check if you may possibly have a leak in the engine water pump. That's a general weak area in the Prius and that most likely is the cause of your low coolant.

If you don't want to change out the coolant when you replace your 3 way valve, just use clamps to pinch the 3 hoses while changing out the valve.

 

When you stand in front of your engine, it'll be on the far left side. There's an engine belt and a pulley. That is the thing that drives the water pump. It's a very simple repair, and one you probably want to address at the same time as the 3 way valve....because you'll be draining coolant again.

You can tell if it's leaking or not by looking around the area for pinkish or whitish deposits. That's usually dried coolant that's leaked out.

 

How much coolant did you add? Definitely find that leak. Running low on coolant can harm the three way valve, I hear.

You can find threads and Youtube videos on how to bleed the engine coolant by running the CHRS pump. The easiest and most versatile way is to buy a MiniVCI cable for $25 and use an old laptop with it. You also need a small tube from the radiator bleeder valve to the filler neck.

 

You may still want to go through the bleeding process. The CHRS may have air in it, which will eventually cause that electric pump to fail. You may notice cavitation (screeching) sounds at cold start-up and at shut down. You still should consider replacing the three-way valve, too. Intermittent problems with that valve are very common, and now that it's been dry at least once it will probably fail soon. That could leave you without cabin heat, and will definitely negate the operation of the CHRS.