How to diagnose 'check engine' light?
 

I have to do a smog check on my '99 E430 in several weeks. The check engine light has been on for awhile and needs to be fixed. It used to be fixable by either adjusting the gas cap or rubbing vasoline on the cap gasket. I replaced the cap to no avail. Is there a port for the OBDII diagnostics I can plug into? Where is it located?

thx

the port is under a little cover above the drivers feet area? do you have an obd 2 scan tool? are you in san diego? i brought my generic scanner home from work i could try to scan it for you if you are close

I found the port, went to AutoZone and scanned. 2 codes came up: P0170, & P0173, which refer to 'fuel trim malfunction', banks 1 & 2. I'm thinking this is the O2 sensors, but how to dianose from here?

with out proper diag hard to say, but normally when you see those codes it if from the airmass sensor, did it specify part load or at idle? if you do replace the airmass sensor be sure to do the filter as well

Answer
 

Best guess:
Breather hoses broken, loose or failing to seal..
This allows unregulated air to enter the system = P0173


Vehicle: 1999 Mercedes Benz E 430 Sedan
Part: Breather Hose
----------------------------------------------------
Breather Hose
Partial load
crankcase ventilation
-----------------------------------------------------
Breather Hose
Partial load
crankcase ventilation
-----------------------------------------------------
Breather Hose
Partial load
crankcase ventilation
-----------------------------------------------------
Breather Hose
Full load
crankcase ventilation


http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1US0YZ0AN1UU0Z62DB&year=1999&make=MB&model=E-430-001&category=B&part=Breather+Hose

Breather hoses? Can you be more specific? That would be excellent if a hose would fix the problem.

Also- does anyone out there know what the correct part number is for the maf sensor? I found several sites on-line with Bosch parts, but the p/n are different. B3130-161380 and BSH074590

thx

OK I finally saw the link on hoses but how to locate them on the car...

they are connected to the valve covers. honestly, nothing bad directed toward whunter, but i have never had to replace them for this issue. usually they will break during service or when you remove valve covers or the intake tube. as i asked earlier, are you near san diego? i would assist if you are close.
the hoses can cause it, but i would inspect them thouroughly for cracks or damage before replacing them. also proper diagnosis will reveal the correct issues. without going with the shot gun approach.

Hmmm
 

My point was to inspect all of the hoses, only replace as needed..

hopefully he understands that, usually most people look for the cheap or least expensive fix first. and often it isn't the cause and they waste time and money. i am offering to help him diagnose the issue if he is close.

Yes
 

I noted this.
My hope is that you are near enough to help.

... the other side of these equation of lean running due to vac leak
[ unmetered air] is a simple check of the fuel pressure regulator.. a bad one will cause the same condition/codes , but on the rich side...........
Best test for this is fuel pressure gauge at test port, but a simple quicky indicator is to pull the vac line off pressure reg. and see if there is gas /fumes in the line.. if so , the reg. is ruptured [ allowing both high/unchecked pressure to injectors and unmetered fuel sucked into intake through the reg vac line.