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Solved: Toyota Prius P2601 Cooling System Range/Performance

There are many threads on Priuschat about this code, but what are all the causes? What else can cause those codes and how can you know what needs to be repaired? On our 2006 Toyota Prius we solved the issue and here is what we found.

When Toyota Prius owners have a problem and a trouble code P2601, they immediately think the electric water pump is at fault. The code description is for a cooling system "range/performance" problem which would signify that the electronic water pump has failed, right? Not always.

In this article, we will take a look at why a P2601 has more than one reason to trip and how you can know what to do if it occurs.

What Is A P2601 Trouble Code?
Coolant Pump "A" Control Circuit Performance/Stuck Off. The coolant heat storage system uses an electric pump to supply hot coolant stored in the CHS tank into the engine's cylinder head. This optimizes engine starting combustion and reduce the amount of unburned gas discharged while the engine is started.

Before the engine starts, the ECM operates the electric water pump to direct the hot coolant in the CHS tank into the engine to heat the cylinder head (this process is called "preheat mode"). This system consists of the CHS tank, CHS water pump, CHS tank outlet temperature sensor, water valve, and a soak timer built in the ECM.

The enabling condition for the code happens when: The difference in CHS tank outlet coolant temperature before and after CHS water pump ON; Less than 1°C (1.8°F). Variation in CHS tank outlet temperature and engine coolant temperature before and after preheating. 2°C (3.6°F) or less. (reference Prodemand by Mitchell1)

So that is what enables the trouble code, but how does the temperature get swayed by 1.8 degrees?

Causes Of A P2601 Trouble Code
Many people on Priuschat are proponents of shotgunning parts without first inspecting or testing. Most of these people would say that the electric water pump on the CHS needs to be replaced, but why? What did you test, and what data do you have supporting that claim?

There are times when that pump fails, but it is pretty rare for it to happen most of the time. So what are the other causes of the trouble code being set? Well, what if your mechanical water pump was leaking and introducing cold air into the cooling system? Bingo, this can certainly be a factor in the P2601 game, and I proved it.

Finding Fault Where Fault Is Due
One of the enabling conditions is because the coolant temperature is different with the engine on and the water pump is running. If there is a leak like the one you see below on the water pump I just replaced, chances are you will get an air pocket into the cooling system.

2006 Toyota Prius water pump

When this happens, the temperature difference between the air and coolant will be more than 1.8 degrees. Trouble code? Yes.

I pulled off our severely beaten mechanical water pump, installed a new one, and vacuum filled the system. We now have no leaks and no trouble codes. I have run the car and driven it extensively with no return of this code.

Take a look at this chart here. Mitchell Prodemand shows the top trouble codes listed over time, with the mechanical water pump being one of them. I recommend testing and checking your components before shotgunning parts; this will save you a ton of time and money.

Mitchell Prodemand Highest cause for p2601

I highly recommend watching my YouTube video on this replacement and see just how bad the pump failed before it was replaced. If you need more help solving your P2601 code on your Toyota Prius, let me know, and I am happy to help.

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Peter Neilson is an automotive consultant specializing in electric cars and hybrid battery technologies. He holds a Bachelor of Science in Automotive Service Technology from Weber State University. Peter can be reached on Linkedin and you can tweet him at The_hybrid_guy on Twitter. Find his page on Facebook at Certified Auto Consulting. Read more of Peter's stories at Toyota news coverage on Torque News. Search Toyota Prius Torque News for more in depth Prius coverage from our reporter.