If you are a newer mechanic or getting more educated about diagnosing emissions systems through the OBD-II diagnosis system, you may have come across the phrase “drive cycle.” A drive cycle is a term used to test whether repairs to emissions-related parts were successfully recognized by the powertrain control module or PCM. The examination itself involves a test drive unique to each car manufacturer. When it is done as directed, it will assist reset the sensors and monitoring equipment inside the PCM and help the mechanic know if the repairs were done correctly.
While it would be great and convenient for the drive cycle to be consistent and easy to follow, in truth it is unique for every car manufacturer. Any responsible mechanic understands that the best resource for getting the exact drive cycle instructions for the car they are servicing is the service and repair manual or software program.
As such, the drive cycle instructions we’ve put below are 5 GENERAL STEPS and should NOT be seen as exact steps to follow. Always refer to your car service manual or a professional mechanic who has access to the exact drive cycle instructions — and follow them to ensure accuracy. In most situations, a correct drive cycle will take no longer than 15 minutes to complete.
Step 1: Complete Repairs and Clear all Fault Codes
This is the step that many inexperienced mechanics seem to forget — but it’s the most vital. After completing any emissions-related service, you have to clear all OBD-II diagnosis fault codes by using a professional digital scanner. This needs to be done prior to beginning the actual drive cycle test.
Step 2: Preparing the Car
The next step is to prepare the car for an efficient drive cycle test. There are a few general items that have to be completed in order for the drive cycle test to be effective:
- Ensure the fuel level is between 30 and 70 percent. If you have completed repairs to emissions systems, especially the EVAP canister or other fuel tank parts, the PCM will need a specific amount of fuel/vapor to ensure accurate measurements.
- Be sure your battery and alternator are in good shape. Jump-starting a car can be a death sentence for the PCM. It can equally negatively impact the drive cycle test.
- Let the car sit for more than 8 hours. The first step of the drive cycle is a cold start. In order for the test to start, the engine temperature has to match the outside ambient temperature. It’s equally important to keep the car in a temperature-controlled area.
- Double check the keys and doors. Before you leave the car for the evening, ensure you have all doors closed and no keys inserted into the ignition or locks.
Step 3: Finish the Cold Start
The cold start is just that: an opportunity to start the engine when it’s truly cold. To finish a successful cold start, follow your specific manufacturer’s steps, as each one is unique. Posted below are a few general steps that most drive cycle tests need:
- Start the car in Park or Neutral
- Let the car idle for a few minutes
- Turn on heater, headlights, and front/rear defroster to maximum settings
- Let car heat up to recommended operating temperature
Step 4: Start the road test
The road test of a typical drive cycle involves a highway and two road driving sessions. The first phase will be a short city driving test. In this particular step, you’ll slowly accelerate to (generally) 25 miles per hour. Anytime you stop the car — for stop signs, traffic, or other reasons — come to a complete stop before furthering.
The second step has to do with a short highway test. Here you’ll want to slowly accelerate to the recommended speed (again, that recommended by your manufacturer) and hold that steady speed for five miles or more. The most important component of the highway test is slowing down. Most manufacturers recommend simply removing your foot from the accelerator, without pressing the brake pedal, until you decelerate to at least 20 mph — then you can slowly press the brake pedal.
The third road test is a return to city driving, where you repeat what you drove in the first city road test. Once the road test has been finished, pull into a parking spot, let the engine idle for a few minutes, and then shut off the engine.
Step 5: Finish the Final Scan for Error Codes
Then comes the last step of the general drive cycle test which is to complete a final OBD-II scan for trouble codes. This is something that will verify that the drive cycle test has been finished successfully. Sometimes a drive cycle test will discover other hidden emission problems that did not register initially.
The most vital step to complete is following the exact instructions as recommended by your car manufacturer. While the information above is very accurate in general, it is not a proven method for all years, makes, and models. When in doubt, be sure refer to the advice from a professional mechanic.