Hi,

I have a 96' 300D with 139k miles and I recently replaced both intake flap valves. Immediately after the replacement of the intake flaps, the transmission shifts very rough (jerky) and I then got a P0400 code.

Could it be a vacuum hose that is disconnected? If so, which one?

I did notice that one of the original intake flap part #'s was 606-140-02-31 and the Dealership provided part # 606-140-04-31 for my VIN #. Could this be the problem?

I really would appreciate any guidance since I have been trying to resolve this problem for a while. Thanks so much!

Louis

Look up a detailed description of the code, it will tell you a lot. Some may know this code by heart but others can point you in the correct direction with just a detailed code description.

P0400 is a general 'hey there's something wrong with the transmission code'.

Factory scan tools, or something like an Autel, Verus, Autologic, or the like, will get the more specific code.

__________________
1997 E300 Diesel - 222K miles

ALSO, when there is a transmission code present, many manufactures will max out line pressures, causing a harsh shift condition.

__________________
1997 E300 Diesel - 222K miles

I didn’t know a ‘96 E300 with 722.4 could throw a transmission code. AFAIK, there are no transmission electronics. Maybe there’s a control valve sensor.

The 722.4 in the ‘96 E300 doesn’t rely on manifold vacuum. Engine vacuum pump vacuum goes through a control valve attached to the throttle linkage to simulate manifold vacuum. IIRC the control valve is by the brake master cylinder. One line sources vacuum from the engine vacuum pump, the other line, usually black, goes to the transmission modulator on the driver side of the transmission by the shift linkage. A thicker black line is the control valve vent that doesn’t connect to anything.

Problems with other vacuum consumers can affect the transmission vacuum signal.

Sixto
98 E320s sedan and wagon
02 C320 wagon

I thought '96 was the first year of the 722.6.....? It was also the first year of ODBII diagnostic ports.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

All US 210s have OBD II.

Maybe the 722.6 was a mid-year upgrade. Jeremy’s ‘96 E300 definitely has a 722.4 with VCV. The 722.6 has no vacuum input. The site sponsor shows an aluminum case filter for the ‘96 E300, not the oval plastic filter for the 722.6.

Maybe lpozzo has a ‘96 build ‘97.

Or I got a head start on the eggnog.

lpozzo, is your shifter marked PRND4321 or PRND32?

Sixto
98 E320s sedan and wagon
02 C320 wagon

Every 96 I have ever seen has the 722.4.

P0400 is generic OBD-II related to EGR, according to several hits on a Google search. My '96 e300 has 722.4 4 speed with VCV and shifter marked PRND32.

Vacuum leak affecting multiple systems?

My 96' 300 Diesel was manufactured in March 1996 and the transmission is PRND32.

The transmission shifted incredibly smooth and seamless prior to changing both intake flaps. Could a vacuum hose accidentally been disconnected in removing the intake manifold causing the rough shifting and P0400 code?

The P0400 code indicates EGR issue but I believe it is related to a vacuum issue that happened after changing intake flaps.

What should I look for and what tests can I conduct to identify the issue?

Thanks.

I think your gut is leading you in the right direction. Check the under hood vacuum lines to make sure all are connected properly. Both EGR and transmission shift modulation rely on vacuum from the pump on the front of the engine. EGR malfunctions will make the computer throw code(s). Vacuum leaks will cause transmission shifting issues. It seems possible you created a vacuum leak somewhere when you replaced the flaps. I sure have done stuff like that over the years, leaving or knocking a hose off.

The following diagram is from a 1998 Mitchell publication, courtesy of M-B USA:

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