V9X - Resolved P0401 but P0488 Persists After EGR Clean

[username_unavailabe]

Hey everyone,

Peter here. I’ve run into a specific issue and could really use your expertise. Recently, my car's (V9X engine) dashboard lit up with a check engine light. A quick OBDII scan revealed two codes: P0488 (EGR system, throttle position control - range/performance problem) and P0401 (EGR system - insufficient flow detected).

After a workshop suggested removing the entire engine to access the EGR, I did some digging and found a way to remove just the EGR itself, so I removed it on my own. It was extremely clogged, to the point where I couldn’t manually open the valve. Post-cleaning, the valve seemed to move with little resistance, so I reinstalled it, cleared the codes, and went for a test drive.

When the engine warmed up, the cruise control fault light activated – a precursor to an imminent check engine light in my experience. Sure enough, rescanning brought up the P0488 code again, but this time, no P0401, which suggests the cleaning at least partially worked, or the drive was not long enough for the ecu to detect the fault (~1h drive, between 50km/h and 150km/h, average ~70km/h).

Here’s where I need advice:

1. Has anyone experienced a P0488 (maybe in combination with a P0401)?
2. What troubleshooting steps would you recommend I take next to further diagnose and resolve the persistent P0488 code?
3. How can I effectively test if the EGR valve is opening and closing properly now that it’s been cleaned? Or should I just go for a new one?

Any guidance or shared experiences with this would be incredibly helpful!

Thanks in advance,
Peter

 

[landmannnn]

Very similar experience here. Just put a new valve in as the stepper motor has failed, you now know how to beat that 10mm bolt so it won't take long.

I bought a Pierberg aftermarket valve so it wasn't silly money.

 

[username_unavailabe]

Very similar experience here. Just put a new valve in as the stepper motor has failed, you now know how to beat that 10mm bolt so it won't take long.

I bought a Pierberg aftermarket valve so it wasn't silly money.

Appreciate the insight on the new valve. Did swapping it out take care of the P0488 issue for you? Also, I'm curious, how were you able to determine that the stepper motor was the problem? My OBDII setup is pretty basic and doesn't show EGR position in real-time, so I'm trying to figure out the best way to diagnose this.

EDIT #1: I came across a post suggesting that applying 12V to certain pins should actuate the valve. I'm planning to give this a try next. Here's the post for reference: Hi from Tullamarine

EDIT #2: I attempted the method from EDIT #1, and there was no movement from the valve. It's looking like the stepper motor's gear teeth might be stripped since the motor doesn't seem to engage the valve, but I hear the movement of the motor.

I definitely get what you mean about that 10mm bolt—what a pain! I was using a ratcheting combo wrench, which helped a lot, even though it was a two-click-at-a-time kind of deal. Funny thing, though—I ended up dropping one of my wrenches, and it's now a permanent fixture somewhere in the engine bay.

I spotted a Bilstein aftermarket EGR valve for about 250€. Seems like a fair price, so after EDIT #2 I decided to buy it and install it. Will be posting when the part is in place if the issue is resolved.

Thanks again for the help!

 

[landmannnn]

Yes, both codes went away with the new valve. I didn't take my old one apart, but yes, either a failed stepper motor or stripped gears.
I only managed one click at a time with my ratchet spanner, 2 clicks would have been a luxury.
Worth trying to dig out the dropped spanner with a magnetic tool if you can, it might cause a rattle.

 

[Olpha]

I think you will find that it is the common fault of the EGR actuator shaft failing (see attached photos). It usually fiddles and farts a few times before totally breaking and jamming the valve. This then brings up the P0401 code. I haven't yet found how the shaft itself can be repaired.
When you do change it out it is common to have an EGR coolant fault come up. This is from an air lock in the EGR cooling system and can be rectified by removing the return hose from the EGR system and allowing the air out. Some patience is sometimes required to do this but it will come out.

 

[username_unavailabe]

Hello everyone,
Just a quick update on my end. I successfully installed the new EGR and ran a 2-hour test drive after a reset. Good news: no fault codes in sight, so it seems like the issue is officially resolved.
Thank you for all the helpful insights. Before reconnecting the hoses, I made sure to fill up the EGR with coolant, and everything went smoothly.
The shaft on mine is fine and works as intended. I might take the old one apart just to see what the problem was.
Thanks once again for your assistance.

 

[iank84]

Great result. Can you pull apart the faulty one with some pics please so we can see why they fail. Also any detail on the 3 terminal sensor inside would be really appreciated

 

[username_unavailabe]

Great result. Can you ll apart the faulty one with some pics please so we can see why they fail. Also any detail on the 3 terminal sensor inside would be really appreciated

Hi! I am sorry for the late reply. I still have the faulty one, so I will open it up and take some pics for you in the next 24h. I hope I am not too late.

 

[username_unavailabe]

Hello everyone,

Update time!

I recently took apart the EGR, and here’s what I found.

First up was the valve, which seemed fine at first glance, though it required a surprising amount of force to open — we’re talking both thumbs and a good grip here! I wasn’t too concerned, so I moved on to removing the electric components. That’s where things got tricky. The valve itself was blocking the electronics from coming out of the housing.

After several failed attempts, I gave in to the temptation of “creative destruction” and ended up cutting off the top of the valve. It's not essential for the inspection, after all. I’m sure there’s a more elegant method to remove it, but I was a bit too impatient to dig up a tutorial.

Once the electronics were finally free, I was greeted by a surprise—planetary gears! Sadly, they were made of plastic, but to my disappointment (or relief?), there wasn’t a single broken tooth. I was really hoping to find something wrong at this point, but no, everything looked pristine.

Next up, I hooked up the little electric motor to some power to see if it was functioning. I cut thin slices of aluminum foil, grabbed an 18650 battery, and connected the motor’s poles to the battery using the foil. And voila! The motor started spinning.

That should mean everything is fine, right? Not so fast. I thought maybe the connector was the issue, but after a close inspection, it seemed fine too.

I gave it another shot, trying to connect the foil to the pins, but the connector was too deep to keep everything steady without hitting the wrong pins. So, what next? I soldered wires to both power pins and held them to the battery. To my surprise, the motor worked again.

To my surprise, the motor worked again.


Conclusion? The motor works, the electronics seem fine, but I can’t test the valve anymore because I had to cut it off to reach the internals. My best guess is that the valve was so clogged with soot that it couldn’t open anymore. Even though I cleaned it, the soot must’ve been deep in the mechanism, creating too much friction. Unfortunately, I couldn’t test the motor’s strength accurately either, since I was using an 18650 battery at ~3.65V, and I suspect the motor needs closer to 5V for full power.

If you’ve got any questions or ideas, I’m all ears!

Cheers,
Peter

 

[iank84]

Hi Peter, I replied earlier today but it doesn't appear so here goes again.
Thanks for the good pics. Looking at the undamaged plastic gear, others have reported it damaged. I'm thinking if the valve is stuck shut, the metal drive gear if still turning would likely shred the plastic gear. Could probably get a metal gear printed from a good plastic one.
Can you see how the shaft position is fed back to the ecu? Is there a hall effect chip or any sensor electronics near the moving shaft?
If I can find a male and female connector to buy I could do some waveform/measurement checks to see what signals are sent back to the ecu to keep it happy.

thanks
Ian

 

[username_unavailabe]

Hi Ian,

Unfortunately, I no longer have access to an oscilloscope, so I can't check the exact signal the sensor is producing. However, I’m 99% sure that the three bottom pins are for the sensor. One will be ground, another for power, and the last one for the sensor signal, though I’m not entirely certain which is which.

As for the sensor, it’s an analog switch. You can actually see it in the photos. In the second image, I’ve pressed the switch all the way in. When the EGR is open, the switch either won’t be pressed at all or only slightly. As the valve closes, the sensor gets pressed further in.

The two forked pins are the power and ground for the electric motor.

Now, based on your comment, I’m starting to think the switch might have been the issue all along. I hadn’t considered that before at all. Would you like me to open it up so we can take a closer look?

Thanks,
Peter

 

[iank84]

Thanks Peter, the mystery deepens.
what bit in the assy drives it in?

If it is linear as you press it in, ie doesn't go click like a switch I'm thinking it could be a resistive device like a potentiometer or possibly a hall effect sensor with a magnet passing it.

The question in my mind is it just sending a signal to the ecu to say the valve is open or is it sending a varying signal proportional to how far open the valve is. I'm guessing the later.
If you can disassemble it should give us the answer.
I have an oscilliscope here but not much use to you there.

 

[username_unavailabe]

Thanks Peter, the mystery deepens.
what bit in the assy drives it in?

If it is linear as you press it in, ie doesn't go click like a switch I'm thinking it could be a resistive device like a potentiometer or possibly a hall effect sensor with a magnet passing it.

The question in my mind is it just sending a signal to the ecu to say the valve is open or is it sending a varying signal proportional to how far open the valve is. I'm guessing the later.
If you can disassemble it should give us the answer.
I have an oscilliscope here but not much use to you there.

The part that drives the switch is exactly what I had to cut off to reach the electronics. I’ve circled it in green in the image, and the point where it makes contact is highlighted in blue.

It’s definitely not just an on-off switch. It must be something that continuously changes the value, otherwise, the third pin wouldn’t be necessary.

I’ll try to disassemble it further and send over some pictures soon.

 

[iank84]

The part that drives the switch is exactly what I had to cut off to reach the electronics. I’ve circled it in green in the image, and the point where it makes contact is highlighted in blue.
View attachment 38616


It’s definitely not just an on-off switch. It must be something that continuously changes the value, otherwise, the third pin wouldn’t be necessary.

I’ll try to disassemble it further and send over some pictures soon.

Thanks Peter that makes sense so the offset drive that moves the valve open and closed that is up & down in the pic also drives the sensing thingiey in and out proportional to valve position. Might be just a variable resistor when you get it apart. Thanks again for exploring it.