P0401 code help needed

You're right about what sensor is used for the detection, but then if a problem is detected, it doesn't necessarily mean the sensor is bad. The sensor is there to detect whether there's an EGR flow problem, so the sensor could be fine, doing its job, and telling you there's a problem.

The number shown in your EGR flow test result is the amount the MAP reading went up (i.e. the amount intake manifold vacuum decreased) during a self test, when the car was decelerating, the engine pulling strong vacuum, and then the ECM opened the EGR valve somewhat, which lets exhaust into the manifold so the vacuum should be less.

In a clean, properly functioning system, we usually see the MAP reading change by about 20 kPa when that happens. I cleaned mine (and replaced the valve, which had a rutted ski jump) when my change was more like 10 kPa.

So your change of 0.33 kPa is definitely awful.

So you could start by wondering whether your MAP sensor is working, but that's not a hard question. What is the MAP reading when the engine is off? Atmospheric pressure is about 101 kPa.

What do you see when the engine is normally idling, not charging the battery or doing other work (you can use neutral to be sure of that)? That'll usually be somewhere in the ballpark of 28 kPa.

If those are about the numbers your MAP sensor gives you, then the sensor is clearly A-OK, and you just need to find out why trying to open the EGR valve during deceleration changes the vacuum by such a piddly amount. Either you've still got something pretty clogged, or the valve isn't opening for some reason.

Anybody done anything funny with the EGR wiring? There were some posts at one time from people doing engine swaps who recommended a rearrangement of pins, that turned out to only prevent the valve from working at all, but in a way the ECM could not detect.

 

Is the pipe on the exhaust manifold plugged?

Have a bad MAP sensor?

moto g power ?

 

I can't quite make sense of what you have written here. No live reading of the MAP sensor should ever be near 0.99 kPa—that would be a very strong vacuum—so it seems like you might be thinking of live MAP readings in the same breath as EGR flow test results, which are different.

So would it be possible to take a step back and just say what your live MAP readings are by themselves? With the engine off, it should be around 101 kPa, or whatever your weather channel says your local barometer reading is at the time.

With the engine idling in neutral, I would expect something down in the ballpark of 28 kPa.

Two readings like those would confirm that your MAP sensor is just fine.

The EGR flow test result is not any live kPa pressure reading—it is one pressure reading subtracted from another.

Say that your engine, during a fuel-cut deceleration, is pulling 10 kPa in the manifold, and then the ECM opens the EGR valve some, and the manifold rises to 30 kPa. The result of that test would be 30 − 10 = 20 kPa and that's what will be shown for your EGR flow test. That's very comfortably above the fail limit of 0.99, and indeed a difference around 20 kPa is what we normally see for a freshly-cleaned, functioning system.

Your result looks more like, say, the engine in fuel-cut deceleration was pulling 10 kPa in the manifold, and trying to open the EGR valve made it rise to 10.33. Not gonna make the cut. (I'm not sure, but the 0.33 difference might even be within measurement error, and maybe the valve just didn't open at all.)

 

When you look at the connector that plugs into the valve, the wire that plugs into each terminal should be the same color as it is in the picture here.
Make sure that the red and purple wires have not switched places.

 

Has anyone mentioned the EGR valve ski jump (as @ChapmanF describes it), a little ramp gizmo inside which can wear out?

@2010_Prius_Bro how was the carbon when you cleaned? With your miles I'd be paying close attention to the head gasket. Coolant level is stable? Seller "may" have poured in a stop-leak product.

 

Sounds like prev owner cleaned EGR components but mighta missed intake manifold.

 

The most wonderful thing about physical systems doing physical things is there always turns out to be an explanation, and when you start from what you know about how it works and systematically measure and observe and rule out the possible causes, you find it.

Confirming above that the MAP sensor is ok makes a good start. Now you know you can use it to observe other things.

 

I’ve read here, that the factory engine has a small plate with the car’s VIN, on the back side, near the right end of the engine. @rjparker has a pic of the location, and likely more details.

 

If the wiring has been disturbed, verify pins in the egr connector. Look for displaced or bent pins. Voltage check the two power inputs to the egr to verify power and the fuses feeding it. Possibly ohm out the wiring to the ecm. I might run the egr step test to determine if anything changes.

Simplified:

Vin Plate Location Gen3


Typical Vin Plate: