P261C after egr, intake manifold, throttle body cleaning

Have you seen this:

P261C engine coolant pump b control circuit ow, what does this code mean | PriusChat

You must have drained some of the engine coolant in the cleaning process. Did you refill, attempt to get the air out? What model year is this (avatar doesn't say)?

 

P261C isn't about coolant or air, it's about the voltage being too low on a control circuit between the ECM and the water pump. It could indicate that the wire harness was disturbed and hasn't made good electrical contact on reconnection (or even didn't get reconnected). Given that the water pump connector is on that leg of wire harness that is in the way for taking the manifold out, I can see how that might happen.

I would re-check that connection before anything else, and then go ahead and look at voltages. There is information on the control of the pump in this thread, and there are 14 pages of workup suggestions in the repair manual for this code.

The most convenient place to stick a meter or scope on the WPI and WPO circuits turns out to be where they go through this connector in the fuse box:

 

There might be air pockets. Being a 2011, it maybe still has the air bleed bolt (was deleted in model year 2012 if I'm not mistaken): look more-or-less right above the egr valve/cooler, for a white plastic, knurled edge knob and spigot. You can push tubing onto the spigot (if it's there), then open that plastic bolt, squeeze hoses, see if you can vent air and get reservoir level to drop a bit. If you don't have the vent bolt, just pulling off one of the topmost hoses, you can accomplish the same venting.

There's more info on what to do after a coolant change, in the attachment.

 

The most important thing in the fill and burp of a Gen 3 is that you fill to the B line (it is above F and used only for this process), cap the bottle, and run the engine up to full operating temperature and at least seven minutes longer. The first couple years of the generation had an additional bleed valve in the hose fitting above the EGR cooler, but for 2012 and later Toyota seems to have concluded it wasn't necessary. Somebody with access to the 2012 manual might usefully check to see if they changed anything in the fill and burp instructions at the same time.

If the burping went well, once the engine is shut off and has completely cooled to the surrounding temperature again, you should see that the coolant in the bottle has dropped from the B line to the F line, having traded places with the air that was in the system.

The WPI (green wire) and WPO (blue wire) circuits are separate: WPO is a signal from the ECM to the pump telling the pump how fast to run, and WPI is a signal from the pump to the ECM reporting how fast the pump really is running.

You would measure either one of those signals independently, with respect to body ground. WPO has an internal pullup at the pump to +12 V and the ECM pulls it down to send the "go this fast" signal. Conversely, the WPI signal is pulled up inside the ECM, and pulled down by the pump to send the "I'm going this fast" signal. So if you were to open the circuits, with power otherwise supplied, you would see +12 V on the pump side of the WPO circuit, and the ECM side of the WPI circuit.

The signals are easiest to watch with an oscilloscope. WPI will be a square wave with a frequency that changes, proportionally to the speed of the pump. WPO has a more constant frequency (around 25 Hz if I remember right), and it is a square wave when the ECM wants half speed, but the % of time at the high level is the requested speed, so it will be narrower when requesting lower than half speed, and wider when requesting more.

You won't be able to see any of that detail with a plain multimeter, but you should be able to see if there is some gross short or open in the circuit.

If any of that didn't make total sense, maybe you have a buddy with an electronics background who could help out for a beer or something?

 

It's advantageous to preemptively drain a bit of coolant before disconnecting the EGR cooler, leaves it high and dry. Also, Throttle body does not really need coolant hoses disconnected. More info in the EGR link in my signature.

 

Yeah that's a puzzle. I did our engine coolant last fall, and did open the vent when refilling. I can't recall holding my hand to feel for air coming out as I filled, but at some point coolant did start coming out (I had a short length of surgical tubing pushed on, for neatness and visibility), and then I closed the vent. Intuitively I'd think it helps, gives the air an exit.

I also screwed up the instruction, leaving the cap off during the warm up in maintenance mode, will keep that in mind next time (5 years down the road, if...).

 

About the 2012 change, I'm curious whether they changed the instructions at all when they did away with that valve. Only I have a 2010 and I don't keep my TIS subscription paid up all the time, so I'm not quite curious enough to go drop another $20 just to find that out.

What I'm more surprised by is how after all this time, there also hasn't been anybody who has a 2012+ who has been curious enough to go find out.

 

Computer geeks often will have some electronics under their belts. It was a required part of my degree. (Plus it was interesting; I wasn't like "aw, geez, why do I hafta study this?".) Can't hurt to ask.

Also there could be some hobbyist or 'maker' groups in your area where you could introduce yourself and say you're trying to work through a certain test procedure and you'd like to understand it better.

That looks like a successful test of the NWP/WPI circuit.

I don't see where you've done the same test of the WPO/SWP circuit. It's a little trickier because the pullup for that one is in the pump, so an equivalent test would be with the pump connector in place and the ECM connector unplugged, but of course the ECM connector has a bunch of other circuits as well and the ECM will think it's weird to have those go missing. (You also need power to the pump, but that comes straight from the fuse box, not through the ECM.)

Why did you not disconnect the ECM connector? If we're looking at the same procedure, step (a) is to disconnect the WP end and (b) is to disconnect the ECM end, so the resistance check you're doing is of the wire harness in isolation.

The 1.66 Ω reading to ground would make me scowl, if I saw it in isolated conditions, but having it connected to the ECM at one end makes it harder to interpret. It would be worth rechecking with the wiring disconnected at both ends.

 

Sounds like you found the problem.

Most of those connectors have double locking methods for the terminals. There will be a primary retention lance per terminal, that has to be squeezed for that terminal to come out. Sometimes the primary lance is formed on the terminal and clicks into the housing; sometimes it is formed in the housing and clicks into the terminal.

In addition, there will be a "secondary retention mechanism" that is part of the housing and locks all of the terminals until you release it. Usually it looks like some straight flat plastic piece the width of the housing, sometimes a different color of plastic, with one or two spots where you can get a small pick under it and pull it up. In the water pump connector it might be a piece you see when you look into the end, and you can grab it with a pick and pull it right out.

You can check this post here for an example of what the wiring diagram manual will show you when you look up the water pump connector. (example only: this is a different connector)



You can see that it points out how the terminal locking works. In this example, the primary lance is a part of the housing that clicks into the terminal, and the diagram is showing you how to lift it with a small tool inserted from the front. You can see the diagram will also give you the part number for the "repair wire" (they sell it as a short length of wire already factory-crimped into the proper terminal), and part numbers for the proper splice parts to use to splice the repair wire to your existing harness. The repair wire is long enough to let you go back into the harness some distance from where the wire broke off the terminal, and make sure you are splicing to good wire.

This wiki page has more information on getting access to the online wiring diagram where you'll find that information for your connector. There are PDF versions of the EWD you might be able to find, but they generally don't include all those down-to-the-connector-and-terminal details; those are just online.

Sometimes the person at your dealership parts counter will look up the terminal details online for you if you don't have them. That can get to be like the telephone game though.

 

Is it normal to get P261C after clearing code P261B "Coolant Pump B Control Circuit Range/Performance"? I replaced the water pump after the B code and now I'm getting the C code. I also checked the 30 amp fuse and it's fine. Replacing the pump seems to have cleared the ! warning light and check engine code.

 

P261C, as discussed upthread, is an electrical connection issue. I would suspect that during water pump replacement, that connector wasn't completely reseated, or it was but the terminals are oxidized or making poor contact, or (as the earlier poster found) one of the wire connections to the terminal in the connector housing got bad, maybe from the unplugging/reconnecting motions when the pump was replaced.

Electrical troubleshooting skills are the right ones to deploy on a P261C.

 

Thanks. I did reseat it thinking the same thing, but I can't say I inspected for corrosion. Can you recommend a spray to clean up wire corrosion? With the check engine light gone, is the code just stored in the system? Hmm actually I cleared it several times and it keeps coming back so that can't be it.

The pump did fix my intermittent lack of propulsion issue (check hybrid light and ! light).