M112. P0400 - EGR Line malfunction error

Thanks loubapache!
As a resume for P0400 issue.
I see the following major steps how to fix it.

1 - Checking and cleaning EGR pipe.
Remove an EGR valve with EGR pipe (very big chance that pipe will be clogged).

Clean the pipe by wire with Seafoam or any other appropriate cleaners.

If you don’t want to waste your time for cleaning those parts then check this parts list. I highlighted required parts, which you have to buy anyway.
EGR valve part# A1121400460
EGR pipe part# A1121400108
Gasket for EGR valve - A1121420280
Gasket for EGR pipe - A1121412180
Screw for EGR pipe - N910143006001 – 2pc. Replace those bolts (Torque spec is 9Nm).

2 - Checking and cleaning holes under breather covers. I would call this step as required after 100k miles.
You can simple remove, clean up and reseal breather covers.
Don't forget to put new aluminum bolts:
aluminum bolt - N000912005010 - 5pc. (Torque spec is 4Nm).
DON'T reuse old ones. You don't want to spend your time for removing broken bolt from the cover (Even 4Nm is enough for cutting those bolt's head). Don't ask me how I know that .
You can combine this step with R&R new valves cover gasket (after 10 years rubber gasket will be like a plastic and definitely it will leak somewhere). Additional point for completely removing valves cover - you can check and clean, if it necessary, the oils channels - small pipes under left cover.

This is final list of parts, which were replaced for three P0400 sessions :
1120180182 1 hose
1120180282 1 hose
1120180382 1 hose
1120180209 1 connector
1179901578 3 connector
1120160321 1 right cylinder head cover gasket
1120160221 1 left cylinder head cover gasket
1110180080 1 gasket for oil cap
1121590080 1 gasket for air pipe.
N000912005010 5 bolts for breather cover

N910143006001 2 screw for EGR valve.
A1121420280 1 gasket for EGR valve
A1121412180 1 gasket for EGR pipe
A1121400460 1 EGR valve


As part of preventive maintenance I'm going to "clean" those holes by cooper/aluminum wire or teeth-stick every B-Service.

Is it common to have oil leak through the valve cover

My E240(1999) has done 140,000km and the engine oil was replaced about 5000km ago with Shell Helix HX7 10W-40.

I have just found some oil leak around the oil cap, the valve cover casket beneath the oil cap.

First, I wonder if the oil leak started with use of 10W-40 instead of Mobil 1 0W-40 or if the valve gaskets are scheduled to be changed every 10 years or 150,000km.

Secondly, the valve cover posted here seems to have a lot of oil residue like my E240, which I first thought it was the outcome of using alcohol mixed fuel (5 to 10% alcohol in fuel) by the previous owner as it contains some sugar.
I also have 1985 380SE which valve cover gasket was changed a week ago and I did not see any sticky residue in the both covers (I have used only 98 High Octane fuel).

Finally, does the seal thread in the valve cover need to be heated before putting new gaskets? If don't, may oil leak occur? After changing the valve cover gaskets and washers in my 380SE, I still see some oil leak through the gasket. Possibly, because the valve cover was not heated before putting the new gaskets.
b. With heat gun, worm a seal thread. I heated cover approximately 3…5 minutes and then push a breather cover by flat screwdriver.

Thanks for the info on cleaning those tiny openings in the breather covers. I just did mine with a fine bit of wire. They weren't as badly occluded as the ones you showed, though. Also replaced valve cover gaskets on both sides, which clearly needed doing, and all breather hoses. I did the spark plugs and wires as well. Now everything is great, except that I've still got the p0400 code. Sigh...I guess I need to go after the EGR now as well.

By the way, if anyone is reading this and considering doing the valve cover gasket job, I'd suggest undoing the fuel line on the left (driver's) side. I tried to snake the valve cover in there, and the gasket must have come out of the groove on the back side. Blew out a couple of quarts of oil, which then ran along the underside of the car. What a mess. That also meant going to the dealer for a gasket priced at $54, as opposed to the identical genuine Mercedes part bought online for $14.

The fuel line comes off with a 17mm crescent wrench, and makes the job immeasurably easier. I'd suggest removing it before you take off the valve cover. You'll also want a rag handy because it's going to leak a bit of fuel.

EGR Diagnosis and Tube Replacement

Thanks to everyone for their help and guidance on this website. Maybe it's my weak search skills, but I didn't find a consolidated DIY for the EGR system and P0400 code. This page is the only one in the W210 Stickys that mentions EGR, but it's mainly about the breathers and valve covers. It took lots of scanning, many links, and lots of time to piece together fragments from various contributors about EGR diagnosis. At the risk of perpetuating this problem, here's my fragment.

Do some EGR Diagnosis before buying or replacing parts:

Test the EGR valve itself by applying vacuum directly to its hose. If the engine almost stalls, then the EGR valve itself is working and the EGR Tube is sufficiently clear. If the idle drops just a little, then the EGR Valve is working, but the EGR Tube is probably almost blocked. (At 150,000 Miles, my EGR Tube was almost entirely blocked, but the EGR Valve seemed fine).

Test the EGR Changeover Valve (0025401897) which governs the flow of vacuum to the EGR valve from the manifold. After reconnecting any hoses disconnected above, apply vacuum to the 'manifold' side of the Changeover Valve. It should hold vacuum when the Changeover Valve isn't energized. Then, apply 12 volts to the electrical contacts of the Changeover Valve (remove the connector and use suitable mini clips to connect a 12 volt source ... not sure whether polarity matters). You should hear a click as the Changeover Valve opens, and vacuum should suddenly flow, thus causing the needle on the vacuum gauge to drop. If this happens, then the Changeover Valve is good.

Now remove the EGR Tube which is probably clogged if you have 100K miles on the car. When I started to loosen the compression nut (which connects the tube to the top of the EGR Valve), the EGR tube wanted to rotate with the nut, thus stretching the accordion portion of the tube. I was afraid of tearing the accordion! Sure, the accordion is meant to flex, but it's 17 years, and a new one costs $117! So I clamped the EGR Tube to the Fuel Rail with a standard Hose Clamp. This prevented the EGR tube from rotating. The compression fitting then popped loose without stressing the accordion.

BTW - I was somewhat wary of clamping to the fuel line, but it worked fine.

BTW - I have a cheap set of "claw foot" open end wrenches that made it easy to loosen the big compression nut. Not sure whether you could swing an open end wrench in there!

Now, both ends of the EGR Tube are free, but, as JFREEZN suggested, remove the 'vacuum distribution block' (a.k.a. "Partial Load Crankcase Ventilation" a.k.a Air Distribution Hose Connector" - part number 1120180009) from the top of the throttle body to provide clearance that lets you rotate the EGR Tube upward and remove it from the intake manifold. The distribution block is easily pried straight up. And thanks for the tip that the 'pitot tube' on the block might snap off ... if so, the broken piece should be removed carefully to avoid dropping it into the intake manifold!). The block only costs a few bucks, and if it leaks, it'll probably cause rough idle. So order a new one before starting the project. You might also want to order a new EGR Tube Gasket (where it enters the manifold), but it's made of something fairly durable, and could probably be reused without leaking.

Hope these extra fragments are helpful to anyone diagnosing their EGR system and the P0400 MIL.