Rep Power: 0

I have searched to no avail. The EGR valve has 5 pins. The two wide apart ones are the coil of the electromagnet. Powering them with 12 volts opens and closes the valve. The three close together are the sensor pins. One gets 5 volts as reference volatge from the computer. One of the others is likely a ground and the third the return signal.

My car has the PO401 code. Before I disassemble the intake side of the motor (I did a head job, 68,000 miles ago and cleaned the EGR passages well), I want to know if the valve sensor circuit is sending the computer the correct value. It is from that very wire that the ECU decides to issue the "low flow" code.

Does anyone know what voltage range the sensor outputs?

PS I also do not want to buy a new valve as a "test".

 
Rep Power: 518

I'd say to use a scanner to read what the computer sees (live engine data). If that doesn't look right, THEN I double check actual voltages at the component in question. (You could have good output from the sensor, but what if that output voltage doesn't reach the computer?)

EGR voltage is usually around 1.00v-1.25v closed.
EGR wide open is usually around 2.80v-3.20v


BUT
Before you bother to test the EGR, you ought to know how this monitor actually works:

During a deceleration event from sufficient speed and RPM at operating temperature,

the EGR valve is pulled wide open while the MAP sensor is read to determine manifold pressure.

If there wasn't enough change in MAP voltage when the EGR was opened, it is determined the EGR system is not flowing a sufficient amount of volume and the P0401 code is set.


My advice, before you get all overly technical with meters and stuff, is see if the EGR passage is really clogged, so you need to be able to judge the size of a vacuum leak by how the engine acts:


Start with a fully warmed up engine.
Pull the brake booster vacuum hose off and start the engine up. See how it acts with a large vacuum leak.
Then use your thumb to cover part of the vacuum leak, make it smaller and see how the engine acts. Try various sizes of vacuum leak with your thumb.
Observe how the engine acts with every change, with various sizes of vacuum leaks.

Experiment, then reassemble the hose so there is no vacuum leak.
Use these observations for the next part below.

Now that you know how the engine acts with various size vacuum leaks, you are going to see how big of a vacuum leak the EGR passages are making when the EGR valve is removed.

Remove the EGR valve from the engine. Start the engine up. Does the idle immediately run up to 2000 and surge hard and rapidly? If it slowly increases to 2k and surges or not at all, the passages are plugged somewhere.

 
Rep Power: 0

Thanks ezone. Your explanation was very informative. I did start the engine with the valve removed and it ran pretty decent. I also sprayed carb cleaner solvent into the passage and was able to fill it leaving a puddle. Guess that indicates a clogged passage. Not likely that the connection between the EGR and ECU is broken. I don't have a scan tool to look at that voltage in real time. I can do it at the valve with fluke, but you are correct in stating I would not know what the computer is seeing.

I want to make sure the valve circuit is good before I go removing the intake manifold. 6th gen cars had a plate that exposed the passages, not so 7th gens. Clogged passages are indeed the most common issue. Guess PCV oil and soot eventually coalesce into a plug.

 
Rep Power: 0

Ezone, so the EGR output that is used for communication with the engine managment computer is only a valve position sensor? If so that means I was wrong to assume the PO401 code is issued as a response to that volatge. A bad EGR sensor circuit would throw a diffrent code as it does have anything to do with measuring or sensing flow.

I saw a tutorial on YouTube were the PO401 code was triggred by a dead 5 VDC pin on the ECU. My deductions from tha video were wrong. One thing, the car in question was NOT a Honda.

 
Rep Power: 518

If you don't have a P0404 or P1491, then the valve circuit is probably good. Those codes are for insufficient valve lift, which normally occurs as a result of a valve that did not open or a bad position sensor.


Correct, if I read that right.


Yep. P0401 is not normally an electrical code, it's a performance code.


I think if there is any wiring issues between the EGR valve and the computer, they would all result in a P0404/P1491 type code on these.

Had one like this last week, a loose fitting terminal at the PCM connector for the EGR position sensor output signal.... Voltage was incorrect when read on the scanner, but double checking at the valve gave me correct readings. Wiggled wires at the PCM and readings came back. Terminal had been spread out inside the connector at the PCM, loose grip, lost contact, bad connection. P1491 code.

 
Rep Power: 0

That's a beautiful thing right there.