You may simply need to drive your C240 just a bit more in order to get its emission monitors (including the oxygen sensor and catalyst monitors) ready for the smog check. Usually driving in both city and highway conditions over the course of a few days is enough to get the drive cycle to run and set the monitors. At times however, due to individual driving habits, following the Mercedes Benz C240 drive cycle below is required. Emission monitors are internal self-tests which the ECM (engine control module) performs to ensure the engine is running efficiently and not polluting.
How To Perform a Mercedes Benz C240 Drive Cycle
Follow the drive cycle carefully. Take extra caution when performing the drive cycle on public roadways. If you feel you will be unable to follow the drive cycle safely, please seek assistance from an smog check repair station or MBZ dealership. They may be able to perform the drive cycle utilizing a dynamometer, and specialized scan tools. Prior to beginning the drive cycle ensure your vehicle has between 15% to 85% fuel in the gas tank, and that the engine is cold. It is best to start the driving cycle in the morning (after a cold soak). Perform the drive cycle below at your own risk.
You'll notice below, the secondary AIR monitor runs when the engine is cold, and best when the vehicle has been sitting overnight. We recommend ensuring the monitor's parameters (requirement for engine to be cold) are being met. If you do not hear the AIR injection pump running in the morning, when the engine is first started and the weather is cold, the AIR injection monitor will not initiate.
Drive Cycle Test Procedure
Note: The drive cycle test needs to be done two (2) consecutive times. Prior to driving the vehicle read the drive cycle instructions carefully and completely to ensure successful test result.
NOTE: Depending on engine temperature you may perform the testing starting with EVAP system (see step 7) or start with steps 1 through 4 or continue to step 6 (Air injection Diagnostics). It's very important to note that these tests are all based on engine temperature.
1. OXYGEN SENSOR HEATER MONITOR
- 02 Sensor Heater Diagnostics (do not interrupt this portion of the test). With the engine warm (greater than 80°C), and the transmission in Park position, proceed as follows:
- Start engine and increase engine speed to between 2,000 to 2,500 RPM for 2 minutes.
- After the 2 minutes, run engine at idle speed, with no applied load for 6 minutes (Air conditioning OFF, no throttle movements, no vehicle movement, etc).
- After this time period has been obtained proceed to step 2 below.
NOTE: If using a Hand-Held Scan Tool verify Step 1 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
2. OXYGEN SENSOR MONITOR
- Lambda (02) Sensor Signal (do not interrupt this portion of the test, to be conducted directly after step 1 above has been performed). With engine temp greater than 80°C, and with transmission lever in position D (DRIVE):
- Drive vehicle for 3 minutes at 43 mph.
- After the 3 minutes has been reached proceed to step 3 below.
NOTE: If using a Hand-Held Scan Tool verify Step 2 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
3. CAT MONITOR
- Catalytic Converter Efficiency Diagnostics (do not interrupt this portion of the test and must be conducted directly after step 2 above has been performed). With engine temp greater than 80°C:
- Drive vehicle with transmission still in position D for 3 minutes at 47-55 mph.
NOTE: If using a Hand-Held Scan Tool verify Step 3 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
4. FUEL ADAPTATION MONITOR
- Self-adjustment of the air/fuel mixture (do not interrupt this portion of the test and must be conducted directly after step 3 has been performed). With engine temp greater than 80°C, proceed as follows:
- Place transmission into Park position and allow engine to idle. ensure no load. (i.e. Air conditioning OFF, power accessories OFF) for 3 minutes. NOTE: If using a Hand-Held Scan Tool verify Step 4 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
5. EGR SYSTEM MONITOR
- EGR System (Emission Vacuum Diagnostics): No DTC codes should stored for the intake manifold pressure sensor and EGR pressure transducer during this portion of the test. With the engine temperature at 80°C:
- Start and Drive vehicle (in D position) and then accelerate smoothly up to 2000 rpm, and then decelerate smoothly back down to 1100
rpm.NOTE: If using a Hand Held Scan Tool to verify test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE. After this test step has been completed, turn ignition OFF, wait 10 seconds and repeat this test step again.
6. AIR INJECTION MONITOR
- Air Injection Diagnostics: (do not interrupt this test when performing this test step 6).
NOTE: It is recommended to perform this test while the engine is cool. You may choose to place a suitable auxiliary fan in front of the vehicle to force engine cooling. Continue test step: With engine temperature less than 40°C, the air conditioning OFF and the transmission in Park position;
- Start engine and accelerate engine speed to 1450 rpm.
- Allow engine to run at this increased rpm until coolant temperature reaches between 70°C to 106°C.
- Allow engine to run with increased rpms for 7 minutes.
- After the 7 minute time period has been reached, stop the vehicle, place gearshift lever into Park position and allow engine to idle (with no load) for 6 seconds.
- Turn the ignition OFF, wait ten seconds and repeat this test step.
- Note that when testing the air injection system, the engine coolant temperature must be at the same temperature as when before the ignition key was switched off in the prior test step.
NOTE: If using a Hand-Held Scan Tool to verify Step 6 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
7. EVAP MONITOR
- Fuel System Leak test (EVAP): No DTC codes should be present in memory for the EVAP canister purge valve, fuel tank pressure sensor, or the shut-off valve.
Note: Prior to performing this test (7) step:
- Ensure the fuel tank fuel level is between 1/4 and 3/4 full and
- The engine temperature less than 100°C with air intake temperature less than 45°C.
- With the transmission in Park position, start and idle engine for 20 minutes, with no load.
- Note that if after the 20 minutes of idling and no readiness codes were set, consider driving the vehicle for an additional 20 minutes.
- After these 20 minutes has elapsed, turn ignition OFF, wait 10 seconds and repeat this test step again.
NOTE: If using a Hand Held Scan Tool to verify Step 7 test completion. This will be indicated by a check mark in the display field or the word PASS or COMPLETE.
Completing the above outlined drive cycle should set the proper readiness flags and complete the necessary emission monitors required to pass the emissions test.
