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.