'94 C280 with 57K miles... with increasing frequency vehicle fails to start.... engine cranks but fails to fire.... or will experience an uncommanded shutdown...as though the ignition system quit.
When running, however, the engine is asymptomatic.

Cylinder head gasket and main engine wiring harness were replaced by M-B in 2000, at 42K miles. Vehicle has run fine, until now.

HHT revealed the following fault codes:

a) Gasoline Engine - failed Quick Check test

Engine management
P1340 CMP sensor
P1335 Engine speed (TNA signal)

Cruise Control
009 Control module CC (N4/3; replace control module)
080 Stop lamp switch (S9/1)
182 Safety fuel shutoff switch signal to HFM (N3/4)

b) Chassis/Drive - no fault codes

c) Body/Access. - no fault codes

d) Climate Control - failed Quick Check test
028 Refrigerant presure sensor
062 Electromagnetic clutch
060 Electromagnetic clutch


(Although codes are listed for climate and cruise control, both systems appear to be working without fault.)

Inspection of engine compartment wiring revealed complete loss of insulation on the air pump's ground wire and partial insulation loss on the pump's power line; no shorting was apparent and the harness has been disconnected from the engine harness.

Inspection of the camshaft position sensor revealed cracks in the sensor's housing; on the basis of this and fault code P1340 the sensor was replaced.

Fuel pump relay was replaced, on principle, and a new air mass sensor was installed. However, the engine still occasionally fails to start or spontaneously shuts down. The shut down is very smooth... one moment the engine is running and the next its not. By contrast, pulling the fuel pump relay results in the engine stumbling and running for a few seconds after the pump stops and the fuel pressure falls.

Any idea as to whats going on here? A "Check Engine" light has not been displayed.

The dealer missed the air pump's harness... are there other specific harnesses within the engine compartment that are prone to failure and should be inspected?

Or is this likely a failing HFM control unit? Any way to definitively diagnosis a bad unit? Will it eventually throw a fault code? Replacement units have to be coded before installation and at $1500 its a must that the diagnosis is correct. TIA.

Sounds like a "faulty" over-voltage relay! Check for the known bad part number.... 000-540-52-45 & get the replacement number... 000-540-67-45.

__________________
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Retired Moderator

Definitly sounds like the OverVolt Protection Relay (OVP).
95% chance this is your problem. It's only about $50 and you can buy it here for cheap!

As for the climate control codes, all the ones you listed are INTERMITTENT... IE it is possible that one of those faults could have occured ONE TIME in the 8 + year life span of the vehicle. They are nothing to worry about, IMO. I would clear them anyway however. Do a search on PBU / N22.

__________________
2006 E350 w/ 155k miles (Daily Driver)

Previous:
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)

Old style OVP relay was present.... installed new style and... no more problems.


Thanks guys!

I have a 96 c220 that won't start either...it cranks but doesn't fire. I had to have it towed to the dealership since it wouldn't start. They say that the HFM control unit is bad, but like the original poster said, that's $1500. If the OVP was bad on my car, would it cause it to not start at all? I haven't checked the part # yet but I did ask the guys at the dealership to verify it was the good part # and they had no idea what I was talking about, and said the ovp tested out okay. I thought I read elsewhere on the site that there was no way to test the OVP...is there?

Dear Mcollie

I had the same problem on my '95 C280. It turned out to be a silver box that simply plugs in to a socket. You will find it on the passenger side of the engine near the firewall. There was a short in the OVP circuit which is also located in the silver box. Some times it would complete a circuit and sometimes it would not. Mostly it would not. It took two seconds to pull the old one out and plug the new one in. I have had no problems since then.

I hope this helps someone out there. I spent $1,000.00 in mech. charges replacing everything from the fuel pump to sensors and my car was down for over 1 month.

Chalk it all up to an experience. Intermittent problems are the hardest of all and it drove both my mech. I nuts.

Best Regards and hope it helps.

I have a 99 C280 with exactly the symptoms described by jgl1. There's no OVP in the 99 models. Can you suggest what I need to do? I already replaced the Air Mass Sensor with no effect. Thanks.

i read that the ovp in a 1994 c280 has a 10 amp fuse...my 1996 2c80 has a 15 amp fuse in the ovp, is this correct? i also have this intermittent abs light coming on and off...it once came on in mid acceleration to 80 mph. was off the following day in the morning...came on briefly in the afternoon after a warm spell in the weather...and when it turned cold in the evening, the following morning it was off again...any thoughts...thanks.

How many different Post/Threads are you going to employ for the same question??

Take the OVP out and see if it is the New part#.

__________________
A Dalton

it is the new part #...but the question is, does it have a 10 amp fuse or 15 amp fuse...?or does it matter...?

<#...but the question is, does it have a 10 amp fuse or 15 amp fuse>

..and .. BUT , the answer depends on if it is the old # or the NEW #..THAT determines if it is a 10A or 15A.
You have a 15A.

__________________
A Dalton

hello, the one in my c280 is the new one...
000-540-67-45 it has a 15 amp fuse.
i saw the same part with the same #000-540-67-45
but had a 10 amp fuse. will the fuse make a difference?
will a model date make a difference? my c280 is a 96.
thanks.

I have answered your question...your chassis uses 15A spec. for the OVP protection Fuse.
Maybe a picture will help.

http://catalog.peachparts.com/ShopByVehicle.epc?q=1996-Mercedes--benz-C--80-Body--Electrical&yearid=1996%40%401996&makeid=63%40%40MERCEDES%2DBENZ%40%4063%40%40MERCEDES%2DBENZ%40%40X&modelid=6335%3AMBC%7C1556%3AED%7C10000015%40%40C280&catid=241959%40%40Body+Electrical&subcatid=242003@@Overload+Relay&mode=PA

__________________
A Dalton

I have a 2000 C280. It started with a random no start that progressed to a random engine shutdown. After a variable amount of time, the car would start and drive normal until the next incident. Replace the crankshaft position sensor (CPS), near the firewall on the bell housing, drivers side. You'll need torx socket, IIRC E8.

glenmore
1990 LS400
1991 300CE
2000 C280

thanks