Mercedes-Benz Forum banner

1 - 11 of 11 Posts

·
Registered
'98 E320
Joined
·
5 Posts
Discussion Starter #1
Most easteregg hunts end by finding something stupid. I'm hoping this is true for my case. I've been battling a P0400 error code for weeks.

First I cleaned the EGR pipe and valve. Still got the code. Then I cleaned the valve again. Still got the code. Took the EGR valve's vacuum tranducer apart (the thing on the valve itself), cleaned it, put it back in. Still got the code. Put a new EGR valve in. Still got the code.

Hours of scouring benzworld and alldatadiy made me think the crank position sensor or MAP sensor might be involved. Alldata says the computer opens the EGR valve to test it; looks for a drop (rise?) in manifold vacuum when it commands the valve to open.

So I tested the MAP and it seemed ok. I had tested it with a Mighty vac and DVOM. I never got an error code for the MAP until I fiddled with it. The next day after testing it, I got a P0105... MAP sensor.... it woke up I guess.

So I decided to test it with engine vacuum and the DVOM instead of the MightyVac. It is supposed to read 4.7 to 5.3VDC between wires 2 and 3 -- it did. It is supposed to read >3.5VDC on wire 1 (signal) with ignition on/engine off -- it did. It is supposed to read <2VDC on wire 1 with idling engine -- it did not. It read the same as it did with engine off (~3.5V).

Did some digging at the front of the intake manifold. The end of the vacuum line from the MAP to the manifold was plugged at the manifold end with the remains of the manifold nipple. The hole in the manifold where the nipple used to be was also plugged with corrosion. Good. No repair required. At least not for this winter beater. If your car is pretty, maybe you should fix it. Anyway......

There was a good nipple right next to the missing/corroded nipple. It is for the air pump switchover valve (I think). So I put a tee in the vacuum line from that nipple and connected the MAP's vacuum hose to the branch of that tee. That seems to have fixed it. Tests fine.

Now I'll have to drive it a few trips to see if that infernal P0400 comes back any more.

The new EGR valve was a waste of money. The crank position sensor I ordered is not; it is inexpensive flame-out repellent. I'm just hoping this fixes the EGR error problem.

The MAP sensor couldn't have been working for a very long time. I have no idea why I never got an error code for it. The computer must have thought the engine was running at wide open throttle all the time, based on the MAP sensor reading.....

I hope this tip helps somebody. I've sucked so much help out of lurking here. Thanks to all for all of it!

I'll post a couple pictures of it.

Paul
 

·
Registered
'01-E320 & 02-ST2
Joined
·
31,631 Posts
Wow. That's kind of bizarre. Good ingenuity to stay after it though.
 

·
Registered
'98 E320
Joined
·
5 Posts
Discussion Starter #4
That's what I thought, too.

In several decades of fooling with varied old machines, I've never seen this happen. Not like that anyway, where both ends get plugged.

I'll sleep like a baby tonight, though. No more trying to figure out where the demon was hiding.

My Benz is to me what word puzzles are to some. There is always a mystery to solve somewhere inside of it.

My buddy suggested it was German pig metal to blame. He said it was probably left over from AMC. I laughed.
 

·
Registered
Currently two W210 E Class 300TD 1998
Joined
·
38 Posts
Hi Paul,
Many thanks for your post/thread. I have a similar problem and might be to do with the MAP sensor. The EGR is on vacuum at idle! So, it’s on all the time. I had three solenoid valves so energized them, and all did nothing... All were open all the time. Hence supplying vacuum to the EGR.

A QUESTION: Did the MAP sensor need energising at 5Volts? Is it a 5Volt sensor - as opposed to a 12Volt - and is there a link to the testing thread that you seem to have been reading please? Or, what wires / colours are what please. The ground on mine didn’t flag as zero resistance to earth.

Now I suspect the MAP sensor is okay because the turbo is working very well. The car is light a bubbly, not heavy and dark. Unless the turbo is on permanently also. No codes from the computer despite me clearing out all codes recently. The major symptom is it fails up hills. However, with the EGR stuck open it would.

I've cleaned out the tank strainer and flushed the tank. Made sure the fuel lines are factory with new O-rings. I've ordered an aftermarket new solenoid valve and hopefully it will be closed at idle? The mysteries of the OM606.962... To be continued...
Many thanks,
Chris
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,710 Posts
The MAP sensor is a 5V device.

If the EGR transducer valve is always open providing vacuum to the EGR valve, then you will get a CEL with P0400.


You could clip close the vacuum line to the EGR valve and see if it makes any difference in performance. In this case you should definitely get an fault code after two driving cycles (considering that the EGR testing conditions are satisfied). Make sure you test the EGR transducer correctly. It has 3 vacuum ports.
 

·
Registered
Currently two W210 E Class 300TD 1998
Joined
·
38 Posts
Hi,

Thank you for that. I doesn't throw out codes very willingly. It’s a 21-year-old car... I suspect if the solenoid valve got stuck on closed, it would throw out a code but three of them have stopped working open... None of them have instigated a code.... The only time I had a code for them was when I blocked off the pipe - effectively clipped it - then the solenoid could sense something wrong... None of the three solenoids changed when 12Volts was applied. The bottom connection to ATMospheric pressure was closed, and the top two to vacuum were connected and open...

Do you know where you got the wire colours and information to allow you to test the MAP sensor safely please?

Many thanks
Chris
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,710 Posts
The solenoid will not sense anything. If the solenoid supply is open or shorted, the IFI (or ECU in the case of a petrol car) will detect it and raise a P1403 almost immediately.


STAR TekInfo

Item 7


here is the explanation of P0105 and P0400.

Items 2 and 13.

STAR TekInfo


MAP:

Blue/red signal
Blue/Black Power
Brown / white ground

Here is the vacuum diagram

STAR TekInfo

Note: Your car has an EGR lifting sender which tells the IFI if the actuator works or not.

To test the EGR transducer see item 24

STAR TekInfo
 

·
Registered
Currently two W210 E Class 300TD 1998
Joined
·
38 Posts
Many thanks, this at least allows me to test the MAP. The computer might be supect becuase it isn't thorowing out codes. It might also be not controlling things as it should... I have another computer but will have to have the chips for entry and ingition changed over beofre I can use it...
 

·
Registered
Currently two W210 E Class 300TD 1998
Joined
·
38 Posts
Do you think I can use a PJ996 lantern battery to test the MAP sensor? It's rated at 6V but its not high amps.
Many thanks
Chris
 

·
Premium Member
1998 E320 base sedan @ 160kmiles
Joined
·
6,710 Posts
The sensor itself is a piezoelectric device requiring small amount of current. I would use USB charger output of my battery booster which is 5V nominal. You can use a USB phone charger after identifying the + and ground wires of a USB cable.

The MAP sensors rarely go bad. You should be able to check the manifold pressure changes from a scanner as you increase / decrease the rpms.
 
1 - 11 of 11 Posts
Top