The OBDII driving cycle is a series of specific driving conditions that your Mercedes-Benz uses to run onboard diagnostic tests. Completing a driving cycle is often necessary to reset your vehicle’s computer system after repairs, clear check engine lights, or ensure your car is ready for emissions testing. While the process needs to be followed precisely, it can be done at home. This guide outlines the procedure for resetting the OBDII driving cycle in your Mercedes-Benz.
It’s important to start with a cold start. This means the engine coolant temperature must be below 122 degrees Fahrenheit (50 degrees Celsius), and the air and coolant temperature sensors should be within 11 degrees Fahrenheit (6 degrees Celsius) of each other. Crucially, ensure the ignition key has not been turned on prior to this cold start, as this could prevent the heated oxygen sensor diagnostic from running correctly.
Once these conditions are met, follow these steps carefully:
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Initial Idle: Start the engine and let it idle in drive for two and a half minutes. Make sure to turn on the air conditioning and rear defrost during this step. This allows the OBDII system to check the oxygen sensor heater circuits, air pump, and EVAP purge system.
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Acceleration Phase: Turn off the A/C and rear defrost. Accelerate smoothly to 55 mph (88 km/h) using about half throttle. During this acceleration, the OBDII system evaluates for ignition misfires, fuel trim accuracy, and canister purge function.
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Steady Speed Monitoring: Maintain a constant speed of 55 mph (88 km/h) for three minutes. In this phase, the OBDII system monitors the Exhaust Gas Recirculation (EGR) system, air pump operation, oxygen sensors performance, and canister purge efficiency.
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Deceleration (Coasting): Without braking or depressing the clutch, let the vehicle coast down to 20 mph (32 km/h). This deceleration phase allows the OBDII to check the EGR and purge functions under changing engine load.
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Re-acceleration: Accelerate again to 55 to 60 mph (88 to 96 km/h) using throttle. The OBDII system re-checks for misfires, fuel trim, and purge system integrity during this second acceleration.
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Extended Steady Speed Monitoring: Hold a steady speed between 55 to 60 mph (88 to 96 km/h) for five minutes. This extended period allows the OBDII system to thoroughly monitor catalytic converter efficiency, misfires, EGR system, fuel trim, oxygen sensors, and purge functions.
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Final Deceleration and Stop: Finally, decelerate and come to a complete stop without using the brakes. This last coast-down allows the OBDII system to perform a final check of the EGR and canister purge systems.
It’s important to note that successfully completing the OBDII driving cycle for your Mercedes-Benz can be challenging. The conditions must be precisely met for each step, and it might require multiple attempts over several days. Patience and careful adherence to these instructions are key to a successful reset. If you continue to experience issues or are unsure about any step, consulting a certified Mercedes-Benz technician is always recommended.
