How Do I Test a Bad Water Pump?

Use a Bluetooth OBDII reader and sync it to your phone. Then download something like the Torque app. Monitor your ICE coolant temperature on hot days and in heavy traffic with a drained, empty traction battery. This will allow you to shut-down and allow the engine to cool down, before getting the CEL or over-temp lamp.

 

I would start by checking the connectors and watching for coolant flow from the bottom hose of the reservoir when it warms up. But I would want to watch the coolant temp with a scanner. Verify it really is not overheating.

A scanner is essential on any car but more so on a hybrid. Knowing the code is number one and knowing what the engine temperature is is number two.

On a variable speed pump you have power and ground and two simple comm lines. You can verify the 12v and ground with a standard meter but it takes a oscilloscope or graphing meter to see the pulses on the other two lines.

Since its a gen4 you need to download accurate test procedures and drawings for $25 from TIS.

It is possible to ohm out the wiring and measure voltages under defined conditions. After the simple tests go to a dealer for an accurate diagnosis if it is not easily fixed. The third teardown is not the charm with head gaskets and overheating.

https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_pageLabel=ti_whats_tis&_nfpb=true

 

There are specific "Repair Manual" procedures that provide steps per code. You can download sections at a time as pdfs. Also detailed schematics "Wiring" with pins and colors.

If its a pending code and you have verified it flows and isn't overheating, clear it and see if it comes back. The water pump gets pulses to set its speed from the ecm and provides pulses to feedback speed. If that control loop is open or shorted it will code but could still be operating.

Four screenshots. Yours could be different.

 

Attached is the engine cooling system section from the Gen 4 Repair Manual. It's from a "static" pdf copy, links broken, but hopefully has what you need for testing the water pump. Let me know if you need other pages.

 

There's more than one water pump error code, saying different things about the water pump. We can always help you best if you include in the post what code you are getting.

No, it's not that easy. You have to understand any specific electric part in order to come up with a workable way of testing that part. This car's engine water pump uses a brushless DC motor with an electronic speed controller having a PWM input and a square wave tachometer output. There really isn't any of that where you'd see a meaningful ohms reading telling you if the thing is good or bad.

You can find more about how the pump is powered and controlled in this thread. (It's about Gen 3, but it doesn't look like the pump is radically different. Pin locations in the fuse box have probably changed.)

Some of the water pump codes (you still haven't said what code you've got) are about the RPM of the pump; there's a code for too high and a code for too low. Pulling it off and watching the pump spin may not tell you a lot, unless you've got a really good eye for RPM (and unless you are holding the pump in a volute filled with coolant).

The thread linked above will show some ways you can test the pump if you have access to such equipment and really want to go that deep, but a lot of the time, just using a scan tool and seeing what codes are reported and maybe watching the target and actual pump RPM will be enough to spot an issue.

 

He says its a P261B

 

Woops, I never saw that quote; link says "conversation not found" for me. Private conversation?

That's the pump RPM too low code.

 

I've been alerted the doc I uploaded above is incomplete; I'll take another look.

 

Maybe cooler heads can have a look at the attached. My "manual" is a cribbed copy, kinda jumbled.

 

Hi Paul, how many miles were on your car when the head gasket blew? Did you ever did a HG repair on a gen 3 Prius? If so, was it mostly the same procedure?