This blog will explain the Mercedes Benz drive cycle procedure and answer the following questions: what is a smog check? When does a vehicle need a smog check?
How do you complete a Mercedes Benz drive cycle?
A Mercedes Benz drive cycle is completed after performing the following steps in the smog check procedure successfully:
- Oxygen sensor heater check
- Lambda signal check
- Catalytic converter efficiency
- EGR system check
- Air intake system check
- Fuel system leak check
Let’s take a closer look at each of the checks required to complete a drive cycle in a Mercedes Benz car:
Oxygen sensor heater check
The oxygen sensor is located upstream and downstream of the catalytic convertor. It needs a small heating element as the sensor is only operating after it reaches a temperature of more than 600 degrees. The heating element brings the oxygen sensor to its operating temperature more quickly so that it will start developing the signal voltage more quickly.
The prerequisite for this step is to bring the engine to operating temperature and the transmission must be in the park position. To complete this check proceeds as follows:
- Keep the engine running at 2000-2500 RPM for 2 min
- After 2 min, let the engine idle and check the actual values of the oxygen sensor heater.
No-load must be applied to the engine during this check, if the actual values of the oxygen sensor are in green or specified range then proceed to the next step.
Lambda signal check
This check is also conducted at an operating temperature of 80 degrees and the transmission should be in drive. To complete this check proceeds as follows:
- Drive the vehicle for a duration of 3- 5 min at partial throttle condition.
- Once the flow and the temperature of the exhaust gases reach a specified value of 400 degrees. The Lambda signal can be checked.
Depending on the vehicle, either a wide band or narrow band lambda probe is used in the exhaust system. The actual values must be within the specified range mentioned in the diagnosis scanner. A handheld tester will either show a green tick or word pass if the check is successful.
Catalytic Converter Efficiency
It is determined by comparing the signals from the upstream and downstream lambda sensors and the engine temperature must be greater than 80 degrees.
- Drive the vehicle under partial load condition for 5 min at 48-60 mph.
There difference between the actual and the specified value of both the sensor must not be more than the specified range given in the diagnosis tool.
Self-adjustment of the air-fuel mixture.
The self-adjustment or adaptation of the mixture formation is determined after measuring the air mass and the signal from the lambda sensors. In some engines, the air mass is calculated from the intake manifold pressure sensor and the air intake temperature sensor.
The mixture formation is checked at the idle condition:
- Put the transmission in P position and let the engine idle for a few minutes. The self-adaptation values must display numbers other than 0.0. For most petrol engines the self-adaptation range is from -4.5 to 4.5.
If the self-adjustment of the mixture formation is out of range in the idle condition; the engine check light comes on. This check is the only success of the self-adjustment is with range and the engine control unit can control the mixture formation based on the signal from the Lambda probe.
EGR system check
This check is applicable to Mercedes Benz models with diesel engines. There should be no fault codes present in the engine control unit related to the air mass sensor and the exhaust gas recirculation valve. To complete this check proceeds as follows:
- Drive the vehicle and gradually increase the engine speed to 2000 RPM and decelerate slowly back to 1000 RPM.
Repeat the process until the exhaust gas and the fresh air mass is within the specified range. If a handheld tester is being used then it will show a pass or green tick in the test menu.
Air intake system checks:
This check is performed after allowing the vehicle to cool down for 3 min. An auxiliary fan is placed in front of the engines and an exhaust gas extraction system is connected to the vehicle. To complete this check proceeds as follows:
- Start the engine and maintain the engine speed between 1200- 1500 RPM
- Keep the engine running at an increased engine speed until the coolant temperature is more than 80 degrees.
- Keep the engine running at 1500-2000 RPM for 7-10 minutes. After 7- 10 minutes let the engine idle for a few seconds.
If all the actual values related to the air intake system are within a specified range then this check is completed successfully.
Fuel system leak test
A visual inspection is performed of the complete fuel system and different components like fuel hoses, fuel pumps and pressure sensors. There must be more than 10 litres of fuel in the tank for this check.
- Start the engine and let idle for more than 10 minutes
- If there are no fault codes related to low pressure in the fuel system then turn off the engine.
What is a smog check?
A smog check is a type of exhaust emission test. It is performed to ensure the vehicles running on the road are not releasing harmful exhaust gases like unburnt hydrocarbons and carbon monoxide into the environment. It can measure the amount and type of pollutants in the exhaust gases of the vehicle
A typical Smog check includes inspection of the following systems:
- Exhaust gas catalytic convertor and sensors
- Inspection of the ignition system, fuel system, air intake system, fuel vapour system and the exhaust gas recirculation system in case of diesel engines and some petrol engines too.
- Exhaust system emissions inspections.
When does a vehicle need a smog check?
A smog check is required whenever a vehicle registration is done or renewed. It can also be required every two years. The following two cases are the exceptions:
- If the age of the vehicle is eight model years and newer, it does not require a smog check.
- Change of ownership smog check is not required for 4 model years and newer vehicles.
A vehicle will be first subjected to a smog check after 8 years from its date of registration. For example, the 2022 Mercedes Benz S Class will require a smog check in the year 2030. If the same car is due for registration, then it will require another smog check after 4 years.
All passenger cars with an internal combustion engine produced after 1976 require a smog check. For vehicles with diesel engines produced before 1997 do not require a smog check.
This blog explained the procedure to complete the Mercedes Benz drive cycle for a successful smog check. If the drive cycle fails then depending on the fault codes further diagnosis is performed. Periodic maintenance is important for the vehicle to complete the drive cycle successfully.