HELP! I've got a recurring P0400...

[ScubaDriver]

My brand new shiny OBDII reader is showing a P0400 (EGR flow malfunction). I clear it, and it comes back. Check engine light is OFF. Truck seems to be running OK. Any ideas would be appreciated.
Thanks,
Roger

[jfreezn]

ScubaDriver - 8/16/2004 7:25 PM

My brand new shiny OBDII reader is showing a P0400 (EGR flow malfunction). I clear it, and it comes back. Check engine light is OFF. Truck seems to be running OK. Any ideas would be appreciated.
Thanks,
Roger

Roger,

I just went through this as the check engine light was on when I bought my 98 ML320. I have a MitiVac and found that there was no vacuum to the EGR control solenoid valve. The solenoid valve is ported to the two EGR valves on a signal from the engine management.

The EGR control solenoid is mounted on the front of the engine, up and inboard from the passenger side cylinder head. On the V6, there are two EGR valves one at the front of each head.

Anyway, looking at the vacuum lines, I found that the vacuum supply line to another device, mounted just below the EGR solenoid was broken almost off the device. It is very hard to see unless you are looking for a break.

Somewhere, back in the tubing harness, these two lines become one, so a leak in one becomes a leak in the other. No vacuum, no EGR function. The car seemed to run fine, just sets a check engine condition.

I hope this is what you find. Cheap to fix! My ML has 127,000 miles on it so may be a guinea pig of sorts.

[ScubaDriver]

I hope that's it, too. Seems easy enough, I'll go through the vacuum lines and see what I find. I'm afraid that without my check engine light on, it may not be a complete EGR failure (the P0400 code is a pending code). Thanks for the advice, looking forward to your experiences with a high mileage ML. I'm at 87,000 miles and planning on keeping it for twice that.
Thanks again,
Roger