While the Honda dealership replaced your vehicle's alternator, its battery was disconnected, and subsequently the vehicle's OBD II emission monitors were erased. Emission monitors are internal self-tests which the ECU (engine control unit) performs to ensure engine emission system(s) are functioning properly.
Setting or making emission monitors ready/complete require specific engine operating conditions are met. The entire process is called a Drive Cycle. In most cases, the monitors should run during normal vehicle operation. However, due to individual driving requirements, the criteria required to run a monitor may not always be met. By following the Honda Accord drive cycle below all emission monitors will run. The drive cycle must be followed accurately.
Take extra caution when performing the drive cycle on public roadways. Perform the drive cycle at your own risk. If you feel you might not be able to perform the drive cycle safely, or obey all traffic laws, seek the assistance of a smog check repair station which will be able to perform the drive cycle on a dynamometer.
How To Perform a 2010 Honda Accord Drive Cycle
Cold Start: Begin from Cold Start, and ignition in OFF position for at least 1 hour. ensure your Honda’s fuel tank is between 1/4 and 3/4 full and engine coolant temperature must be below 122°F and within 11°F of the ambient air temperature. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
Idle Time: Run your ’s engine (do not drive) for 2 1/2 minutes with the air conditioner on and rear defroster on. During this period the ECU will be running the Oxygen Sensor Heater self-test, Air Injection System Passive Air test, EVAP Purge "No Flow" test, Misfire Detection.
Acceleration: Turn off the air conditioner and rear defroster and begin driving. As soon as possible apply half throttle until 55mph is reached. The ECU will now run self-tests on the Misfire Detection, Fuel Trim, and EVAP Purge Flow.
Hold Steady: Now hold your vehicle speed steady at 55mph for three minutes. During this time the Oxygen Sensor O2 response, Air Intrusive (AIS System), EGR Flow, Purge Valve, Misfire Detection, and Fuel Trim diagnostics will be performed.
Deceleration: During this step you want to slowly let off the accelerator pedal. Do not brake or shift your Honda in order to slow down. It is important to let the vehicle coast along gradually slowing down to 20 mph. The ECU will once again self-test the EGR System, EVAP Purge System and Long Term Fuel Trims.
Accelerate: Go ahead and accelerate again at 3/4 throttle until 55-60mph is reached. This will perform the same self tests as during the first acceleration step.
Hold Steady: Hold steady speed once again. This time at 55mph for five minutes. During this time, in addition to running the self-tests as during the first HOLD STEADY step, the ECU will perform the catalyst monitor diagnostics. If the catalyst (Catalytic Converter) is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst,or in order to Complete the CAT Monitor.
Decelerate: This will perform the same diagnostics as in the first Deceleration. Remember not to press your Honda’s brake or shift gears during deceleration.
To ensure all monitors are complete, use a scan tool to view the monitors.