Check Engine Light
 

Hi Guys,
My check engine light is lit. Does it mean my EGR valve is bad? What else could be wrong. My fuel cap seems solid and holding well.

Thanks!

Is this on your S320? What year? Mileage? Any recent work? Condition of plugs? Wiring harness? (M104 harnesses in W140s?)

How's it running? Any changes?

OBD-I or OBD-II? Big difference.

The CE light on OBD-II cars can light for many, many things.

Have you had codes pulled? If not, you'll have to. If OBD-II, think about having an MB dealer or someone with Star Diagnosis System do it, as the tranny/AC/etc has codes that can be stored too. On 722.6 equipped cars, the tranny can light the CE light as well.

There are 26 different systems that can illuminate a check engine light.

The codes change for the different chassis (W124, W140), and model year (OBD-I vs. OBD-II).

You really need to post the model and year of your car.

Hi Guys,
My car is a 1996 S320. I was reading the owners manual, and it says that CE light lits when there is a problem with either emmisions control system or the fuel ingection system..

Any idea what else could it be .. ?

Right.

The check engine light will illuminate for faults related to smog emissions.

Your car will store dozens and dozens of codes, but only fault codes relating to smog emissions will cause the check engine light to come on, and there are 26 different codes that will cause a check engine light.

All cars had to be OBD-II compliant in 1996, but I think your car became OBD-II compliant in 1994 or 1995. I'm just not sure.

If your car is OBD-II compliant, Auto Zone can read your codes for free.

In any event, there are so many different things it could be that you need to get the codes.

You have the same engine and transmission that are in my car, and common problems that cause a check engine light are:

1. EGR valves / hot inlet pipe plugging up.
2. O2 sensor
3. Transmission upshift delay valve

Thanks Paul for your detailed input. Iam amazed to see that auto zone reads errors for free. I will post another reply once i get it checked!

///S320

AZ will read the codes for free, but keep in mind that this is NOT a diagnosis. Most codes point you in the right direction, but don't specify an action to take.

It's a first step, and might work to figure out the problem, but don't be disappointed if it doesn't.

Is it running properly? Have you had any work done recently?

hi Blackmercedes,
I recently got my sparks changed, but the light came on before. Is it always expensive to fix CE related issues?

Thanks

Cylinder Misfire
 

I went to auto zone to get my check engine light checked. The code reader said:

Cylinder misfire on cylinder 1 and 4
Random misfire

Does anyone know what misfire means? what kind of a problem iam looking at and how much would it cost?

Thanks

Here's the problem with going to Autozone. No diagnosis. Misfire cost? Well, it depends on what's wrong. We have no idea.

Have you pulled the plugs? What do they look like? Pay special attention to 1 and 4.

The good thing is that you have narrowed down a little. I would suspect something wrong in the ignition somewhere. This is where it gets tricky. You could spend tons just throwing parts in until the problem is resolved. Or, you can properly figure the problem out. Some things it might be:

Plugs.

Coils.

Plug wires.

Wiring Harness. (W140 too for the M104?)

Have you checked the connections? It might as simple as that.

I don't have much knowledge of the M104, but aren't there three coils? Would 1 and 4 share a coil?

Because you have a random misfire in two cylinders, and because you have an M104 engine produced between the yearas 1993-1995, my best guess is that you have a bad engine wiring harness. Misfires are one of the symptoms of the dread flaking wiring insulation problem.

Do a search on this site for "engine wiring harness" or "wiring harness", and you will find enough posts to keep you up all weekend.

The harness itself is about $500, and expect to pay 2.5 to 3.0 hours for labor at an indendent shop.

Be sure to go to an independent mechanic that specializes in Mercedes. They should be very, very familiar with this problem, and have surely replaced dozens and dozens of harnesses on 3.2 liter M104 engines.

Are the W124 M104 harness and W140 M104 harness the same? What do you want to bet the W140 part is more expensive.

Before going to crazy with expensive parts and diagnostics, change the spark plug boots, about $8 each. I had a misfire diagnosis last year cured by replacing #6 boot.

A wiring harness is an extreme long shot for a random misfire code. If the harness was bad, one would have other symtoms.

Advise given above is good.

When my harness went bad, random fault codes, including misfire codes, was all I had. Eventually the problem gets worse, including hesitation, popping (backfiring through the intake manifold), missing at idle, etc.

Enrique at MB Motors tells me that random codes are always the first symptom of a failing engine wiring harness.