Prius P261B Electric water pump control
Fault P261B for engine coolant pump sets shorty after gas engine starts. Customer states water pump was replaced recently (we are unsure of brand or who did it but it appears to look replaced). I have verified B+ and ground at the pump and can light a bulb on these wires as well. I have 12V on the green wire KOEO (normal). I have scoped the blue wire at pin #10 engine controller (communication signal back to ECU) and have what I consider a normal signal / 0-5 volt square wave when commanding pump on with bidirectional test.
There is a applicable TSB for this fault TS-B-0143-10 but the bulletin only suggests verifying voltage and ground to the pump and replacing the pump…. Being that I appear to have a normal signal when commanding pump on I am a bit nervous about calling to replace the pump
Do I have a faulty ECU or is there something I may be missing here?
Thank You for your time and input!!
You got control. The ECU is commanding it 2550 rpm and it wants to see that. The actual is 0. Powers and grounds? These things fail from 30K to 120K. Check the underside and it might even be melted. You can also bi direction or command it to high rpm and you can hear the motor buzz, whine, or slosh like it wants to and then nothing. Replace. Easy. Tell your customer OEM is best with Super Long…
Hi Bill, I have seen this issue numerous times with both Prius and Camry HV. Typically, the water pump is faulty. It may run, but it can't produce the rpm signal. The reason for the code is that there is no feedback rpm to the PCM. Going from memory, the PCM puts 12 volts on the rpm feedback wire and then the water pump electronics toggles it low. You could toggle it low with a testlight and…
Hi Bill, I would make sure the replacement pump is a OE Toyota or Aisin ( Aisin is the OE manufacture and will have “Toyota” grinded off the aluminum casting, you can see this with a mirror) I would be worried about a non-OE pump. Here's a couple scope captures of a brand new Aisin pump. Hope this helps.
Matt -thank you very much for the scope pattern! I can now see my signal on the green wire is incorrect .
As Matt Lamontagne suggested, replace the pump with an OE one. This pump runs all the time when the the system is “Ready”. Aftermarkets with ⅓ of the price of an OE are tempting but would not last. Just a thought.
Happy to help! I'd love to use this as a case study for training. Shoot me an email at … I'm interested in more info on the faulty part
This scenario is reminiscent of what happens when an aftermarket fan controller is used on a VW or Audi. The inferior quality electronics found in many aftermarket products are unable to recognize either the command signal (fan controllers on Vw/Audi) or unable to provide the required feedback/verification signal to the control unit (what it sounds like is happening here). If wiring between the…