Mercedes-Benz E-Class and E-Class AMG: Why Does My Car Die Right When it Starts Up?

This article applies to the Mercedes-Benz E-Class and E-Class AMG (2002-2009).

When you turn your key to the crank position, your vehicle's starter is powered by the battery and begins to turn your engine at about 300 RPM. During this same time, the vehicle computer references data from sensors, such as the TPS (throttle position sensor) and MAF (mass air flow), to determine the correct amount of fuel to inject into the combustion chamber. The computer also references the crank and cam position sensors. Doing this tells the computer where the piston is at in relation to TDC (top dead center). The computer then has the needed information to correctly time the firing of the spark plugs. If any one of these are missing, your engine may not start.

Always check for trouble codes first using an OBDII scan tool. Once you have the code, you can research the number and will have a guide to follow while making the repair.

Step 1 – Perform a visual inspection

• Remove the engine cover.
• Carefully look at electrical wiring and connectors around the vehicle. If any ground wire connections appear dirty, clean them. Also look for any loose or broken vacuum lines and intake pipes.
• If there is a fluid leak, make sure your fluid levels are correct. Look to see where the fluid is going. For example, if there is engine oil leaking onto a coil pack, it may be causing a misfire.

Step 2 – Verify your starting/charging system is operating correctly

A weak battery and/or a weak alternator may be causing your engine to shut off.

If your vehicle actually runs at idle momentarily, that is a good sign because it eliminates some components from the diagnostic process. It is possible for your battery to be at the point where it can no longer hold a high enough charge to keep the engine running. Unfortunately, unless you have a battery load tester, you're limited on testing options. Most automotive parts stores will load test your battery for free.

This process can be done without a DVOM on the W211. Simply use the display in the instrument cluster to watch the battery voltage. By pressing the button to the left on the cluster, battery voltage should appear.

• Connect your DVOM to the battery with the vehicle off. Positive on positive, negative on negative. The reading should be between 12.2 volts to 12.6 volts. If it is lower, you will need to recharge your battery and try again.
• If a weak battery was your problem, be sure to test the alternator. Connect your DVOM in the same way, and raise the engine RPM to 1,500 with all lights/accessories on and running. This includes A/C, headlights, radio, etc.
• Battery voltage should remain between about 14.2 and 14.6 volts if your alternator is functioning correctly.

Be sure to look over the wiring running from your battery to your alternator for any bends, tears in insulation, and corrosion.

Step 3 – Test the fuel/ignition system

This is a quick test to determine if your fuel system is supplying enough fuel to the engine, or if your spark plugs are firing.

• Spray propane into the air intake stream while cranking the engine. This can be done anywhere on the air intake pipe.
• If the engine now stays running or runs longer, you have a fuel supply issue. You will need to test the fuel pump and injectors.
• It is also possible for the gas in your fuel tank to be of low quality. Pouring in a couple more gallons of fresh gas may cure the problem.

If there is no change in the way the engine runs, then one or more of your spark plugs or coil packs may be faulty.

Step 4 – Clean your MAF sensor and throttle body

Over time, dirt not captured by the air filter gets trapped in these two areas. This restricts air flow to the engine and distorts the sensor's readings, causing the engine to stall.

Cleaning your throttle body does not require much work once the MAF has been removed:

• Continue to remove the MAF sensor buy disconnecting the clips holding the intake pipe to the MAF sensor housing and throttle body. There may also be a hose attached to this pipe, but it does not need to be removed if you do not want to remove the intake pipe from the engine bay.
• Once removed, you can manually open the throttle plate with your hand by pushing on it. Use the throttle body cleaner and a rag to clean any dark residue.

(Related Article: How to Clean Your MAF Sensor - Mbworld.com)

Step 5 – Test the cam and crank sensors

If the sensors are sending the wrong signals to the computer, the engine can stall.

To test the camshaft position sensor, begin by:

• Unplugging the electrical connector and identifying what each pin in the connector is doing.

1. Pin 3 supplies 12 volts (battery voltage).
2. Pin 2 supplies the hall sensor signal (5 volts).
3. Pin 1 supplies ground. ( less than 0.1 volts).