We recently had a 2010 Mercedes E550 roll into the shop because its check engine light came on. This could result from a nearly limitless combination of possibilities, so we hooked the vehicle up to our scan tool and found codes for a couple of common issues on this make and model.
Faulty Sensor
The first was a code for the oxygen – otherwise known as an O2 – sensor. This particular car has 4 oxygen sensors, but after monitoring the car’s live computer data we determined that the O2 sensor on the upstream bank in particular had failed. We ordered the part and replaced this sensor for the customer.
Poor Performance
Another code was for a lean running fuel-to-air ratio. This means that too little fuel is making it into the engine in relation to the amount of air mixing in the cylinders for combustion. The result is a weak, poor-performing motor, or the motor completely stalling out. The problem could originate from either the fuel or the air side of the fuel-to-air equation. On the fuel side, possible issues are a weak fuel pump, fuel leak, or faulty fuel pump relay. Any of these would result in less fuel than intended making it into the engine’s cylinders for combustion. On the air side of the equation, issues are most likely a variation on a vacuum leak allowing more air into the fuel-to-air mixture than intended. This could come from old, cracked vacuum hoses allowing extra air into the system, or something cracked or warped with the engine block also allowing air into what is supposed to be a negative pressure (vacuum) environment.
The vacuum leak is what the issue turned out to be – given the vehicle’s age (12 years) and mileage (155,000), the intake manifold had become warped and was allowing extra air into the system. To find the specific location of the vacuum leaks (and to determine which parts need to be replaced), we hooked up a smoke machine to the vacuum lines. This machine pumps smoke through the vehicle’s vacuum system, and wherever there is a leak, you’ll see smoke rising from that location in the engine bay. Without this smoke machine, it’s nearly impossible to locate a vehicle’s vacuum leak since – unlike fuel or oil – air is of course invisible. To remedy this issue for the owner, we ordered and installed a new intake manifold from the original manufacturer.
Fremont Auto specializes in repairing foreign makes and models, such as this Mercedes E550. If you are experiencing similar issues or something else entirely, please come visit us at 38623 Fremont Blvd #110, Fremont, CA 94536. You can also call us at (510) 793-6067, or email us at FremontForeignAuto@yahoo.com. We use exclusively OEM parts and provide you peace of mind with a 2-year, 24,000-mile parts and service warranty on all our repairs. We hope your car never lets you down, but when it needs serving, please reach out!
