Testing Gen 3 Water Pump

So, code P261C indicates that the ECM detected low voltage at the water pump control circuit. It really helps to understand how this system works. There are 4 terminals at the pump. A power ("12V" turned on or off by the ECM via a relay), a ground, a control signal "from" the ECM, and a feedback (pump RPM) signal "to" the ECM.

AFAIK the control signal is a 5V reference that is made in the pump. The ECM takes that 5V and switches it to 0V at a fixed frequency (many times per second) but changes the percent of time that the signal is high (5V) or low (0V) when it wants to change the pump speed. This is called Duty Cycle control. If the DC is high 10% of the time, then that = one speed request, 50% DC = a different speed,etc.

The controller inside the pump reads whatever the duty cycle is on the control circuit and runs the pump motor at the requested speed. There is a sensor in the pump that reads the motor's speed and this signal is sent back to the ECM on the feedback monitor circuit.

Think of an old movie about big ships on the ocean. The captain on the bridge "rings up" the engine room for "Half speed ahead" on the engine telegraph. The engine room responds "that it has received the request and is responding" with Half speed ahead on the telegraph repeater. But what if the captain tries the telegraph but sees that it's broken?

The P261C code means that the ECM detects less than 5V when it first powers up the water pump, so it can't control pump speed. The controller inside the pump is designed with a fail safe mode where it will turn on the pump motor if it doesn't receive a control DC signal on the control circuit. Pumps made by different companies might respond at different rates to a "lack of control" failure.

I would look at the control circuit wiring and connectors between the pump and ECM, particularly at connector DA2 which I believe is inside the engine room fuse box and is apparently prone to corrosion right there. Resistance testing is of limited value when diagnosing electrical faults. You can get a "reasonable sounding" reading on a multimeter, but have problems when trying to flow adequate current through the circuit. or maybe there's corrosion that partially shorts a (low current) data signal to voltage or ground- but the "short" is only apparent when full voltage is present on all the circuits involved. Summary, measuring voltage on a "live" circuit is preferred when possible or safe to do so.

I mean, if the pump dies completely then that signal won't be there, but I doubt that multiple pumps all have the exact same failure.

 

That description covers the key points, only the pulse trains on the pump control and pump feedback circuits swing between 12 volts and (near) ground, not 5.

There are more details on how the pump is controlled in this post and following.

The 'low' state of the pulse train is still slightly above ground. If you supply a pulse train that actually touches zero in the low state, you will get the code for low signal voltage.

 

Where any or all of the replacement pumps Aisin WPT190? I believe it’s the Toyota supplier. Here’s one source:

Buy Genuine Toyota 161A039015 (161A0-39015) Pump Assy, Engine Water. Prices, fast shipping, photos, weight - Amayama

how many miles btw?

 

^ Good to know. Maybe the relays are collateral damage with failing water pumps: the pump is run constantly in a (vain) attempt to cool, and it over-taxes the relay.

 

Or, because the pump not only has its main power switched by a relay, but is also told by the ECM whether and how fast to run ... maybe the ECM normally is signaling "don't run" at the moments when the relay is switched on or off, so there is minimal arcing at its contacts ... but a wiring fault like a ground fault in the WPO signal could have the pump drawing full power all the time, forcing the relay to switch that.

 

Most 12V relays in automotive use will usually have a suppression resistor or diode across the coil to protect the driver in whatever module controls it. I almost never see anything across the contacts.

Posted via the PriusChat mobile app.

 

Hey which relay is it specifically? Location?

 

Assuming you're here to ask about Gen 3, the relay is the one in the bump off the top left of the underhood fusebox.

 

Could you just do a continuity test on the relay? I just got my new water pump in and it was the AISIN pump With Toyota just ground off and I’m still having the same issue . I connected it straight to power in the motor turns I also went back and checked my other water pumps that I thought were dead and apparently they’re not there either so it’s something in the wiring or it could be this relay so I’ll try your advice and swap the relay and if that doesn’t work I’m just gonna get a Thermo activated relay and just set it for 180 cause I need to drive my car

 

That pump may have a factory defect and ended up sold because someone did a quick check. Others have used multiple aftermarket units that ultimately were all "slightly" flawed.

Others have had ecu failures. Possibly because of jumping 12v power to test and then the power was incorrectly applied to an open collector, current sinking input. Under this scenario, the pump would still run when "jumped" on the plus and minus but a burned current sink could ruin the ecm. It is also possible the pump has a vulnerable current sink.

It would seem that a) the wiring is not 100% on the two wires between the pump and the controlling ecm or, b) the ecm has a smoked control input or output or, c) the aftermarket pump does not exactly meet your vehicle's timing specs. It is conceivable that some ecu versions have more timing tolerance than others. There have been demonstrated cases for each. Sometimes the original part was good but the repair or other activities created additional issues. If you end up with two water pump problems at the same time the diagnostic process really gets sticky.

Clear indications of some wiring issues probably induced by the engine swap.

Not sure I would hack in a temperature control for the pump that would stop coolant flow when the engine is running. Cylinder wall and head hot spots are likely. If I were forced to do something like this (under extreme duress like Nacho on Better Call Saul S6E3) I might have it run continuously when in Ready.

This gen4 into a gen3 swap reminds me of another here where the problems kept compounding. That guy also scattered questions all over the forum such that few had the whole picture, especially problematic when doing a generation swap that most of us have never seen.

I would spend an hour documenting the whole situation from start to finish (or at least to today) in a new post.

 

Thank you so much for your response. Yeah I really don’t know how to write an entire article and post it on here like a lot of people do there’s a lot of pros on here and every time I post something I seem to get on somebody’s nerves but I’m just trying to do the best I can. Yeah I’m just trying to learn as much as I can . This car I use for work I’m an Uber driver and since I did this engine swap which was probably just a big mistake I’ve lost so much money so far and now I’m like just trying to get this car running and I am clueless. I downloaded version 12 of techstream and I tried to use it to start the water pump and it wouldn’t communicate with it I didn’t seem to really communicate with anything except for just give me some general codes back for water pump ,knock sensor ,intake ,air sensor but outside of that it wouldn’t really tell me anything either I need a newer version or I just need to have the ECU reprogrammed I’m calling garages seeing who could do it because Without needing to drive the car. I even looked into some Davies and Craig standalone systems that are pulse modulated to run my water pump. Lol i’m gonna go now and change the coolant temp sensors and double check the wire harness right at the water pump I know the wiring is good because I checked each wire for continuity and they were fine so maybe it’s the connector. Who knows. I guess I’m gonna have to try to keep my threads down to a minimum because posting a different thread seem to aggravate people it’s kind of hard not to when you do an Internet search and it leads you right back to prius chat to a different thread. Then you see somebody on there who Seems very knowledgeable but hasn’t replied to one of your threads and you think well this person knows something so then you try to see if they can help you out. I’m trying to do all I can you know what I mean? Sorry to ramble on.

 

Sometimes, when you're lucky enough to have people actively paying attention to your issue and trying to help you, it can be faster to just respond in those conversations, supply the further measurements and information asked for, and often a solution can be reached.

 

I’m responding to the ones I can relate to .

Do you mean just the water pump situation that I’m at now because the engine is running it’s just a water pump situation that I’m dealing with now. I went to a thread where they talk specifically about a gen 3 water pump. I thought that I would get information that is more specific on that matter. It seems much easier just to ask a person who has just had the same problem than waiting for them to find a thread they’re probably not looking for any more because they don’t have the problem anymore. I do have a thread where I am discussing do you know a general failure from the GEN four GEN three engine swap but there’s really no responses there so I’m not sure what to do I’m getting kind of discouraged about people telling me that I can’t look around and find information on other threads and then I can ask questions. I feel like I’m in a time crunch and I don’t have days to sit around and wait for people who are probably not looking at my problem because they don’t have the same problem anymore. Does that make sense?

hey thanks man I tried to swap the blue relays but nothing different. I’m wondering in the gen 3 could it be the coolant temp sensors that are preventing the ecu from signaling the relays?? I’m gonna go put in two new ones in and see how it works out I’ll let you know.