Can the EGR Circuit be monitored?

not that i recall reading

 

Some cars have EGR flow sensors but I don't think Toyota does it. There may still be a way through indirect measurements. You could almost certainly get something by monitoring the knock counter. One problem with that is that while insufficient EGR flow will increase the knock count, it isn't the only condition that can cause this effect.

 

Toyota does monitor it since they can set the P0401 for Insufficient EGR Flow. With electrically operated egr valves, the engine ecu can test the EGR circuit by forcing it open with the engine idling. This should cause the engine to idle poorly or run rough

If ecu cycling of the valve has no effect on engine idle, the EGR system is plugged up and or the EGR valve has failed.

 

That's the best scenario for the driver.

I've heard from a few sources here that the EGR system can get completely sealed up and not generate a P0401. Maybe the MAP sensor ranges that trigger the P0401 are too lax? How does the pool of oil submerging the MAP sensor affect sensor readings? There's also the buildup of carbon in the intake manifold that should change the distribution of vacuum inside the IM to cause higher pressures before the restriction (at the MAP sensor).

 

Depending on the definition of "monitoring": periodically inspecting just the pipe might do.

@NutzAboutBolts has a video for that, goes through the steps to remove air intake as well.

 

It can be monitored. If the head gasket blows, the EGR is clogged. If the head gasket is operational, the EGR is probably still clogged.

Takeaways, Clean your EGR.

 

Periodically inspecting the pipe is what I plan on doing.

 

Do the main passages in the manifold actually clog to that degree? I understand that the EGR passages can.

 

It can collect in the head after the intake manifold. At 70k mine had stalagmites. IM, EGR cleanse and a few rounds of Techron cleaned it up.

Pixel XL ?

 

Yours was also the subject of more experiments than the rest.

Particularly from a “run it out of gas” perspective .

But the circuit is cleansed now and in good sorts .

 

After seeing that gnarly fuel pump filter photo Raytheeagle posted not too long ago, I'll never let my tank get low again. (Just hoping not to pump a bunch of sediment at once.)

Regarding the monitoring of the EGR circuit via OBD, it would be interesting to see if the max commanded EGR changes before/after cleaning. As in, does the computer know to open the valve more when clogged in order to get what it needs? On my post-cooler-cleaning Prii, the computer never commands more than 60-70% from the EGR valve.

There was a difference before/after on the "EGR flow insufficiency" monitor numbers, but there's currently no easy way to ask for that without using Techstream. (It's likely technically possible with an OBD2 dongle, but might not be as simple as discovering a custom PID for use with Torque. If I were selling Dr. Prius app, I'd definitely look into it. At the very least snoop the USB communication via usbcap while using Techstream to read the value. But I digress... )

The EGR flow insufficiency monitor seems to be a test that runs (occasionally? once after warmup?) in the background, with the results stored by an ECU. As opposed to a sensor that updates in real time.

To add to the list of things we don't quite know, it's not clear AFAIK if the EGR valve has a position sensor. It has a bunch of wires like a throttle (which often uses 2 wires for command, 3 for sensing position). The EGR valve has 6 wires ,so it might have a position sensor. But I don't think the custom PID for EGR Step ever mismatches EGR Commanded (--by more than sampling delay would explain).

TLDR: we don't know how to monitor the EGR circuit, but the pieces might be there.

 

I figured the fuel filter would get some attention .

And remember I never let it get below one bar or wait for the flashi last PIP to let me know to refuel.

Glad it helped .

 

I believe it is a stepper motor.