Facing a failed smog test in California due to “Incomplete” OBDII monitors after a battery disconnection or service? You’re not alone. Many car owners encounter this issue, particularly concerning the Obdii Heated Oxygen Sensor. While your check engine light might be off and no fault codes are present, those incomplete monitors can be a major hurdle in passing the California emissions test.
The problem lies in the fact that after a battery disconnect or code reset, your car’s On-Board Diagnostic system (OBDII) needs to re-run its self-tests, known as “monitors”. These monitors assess various emission control systems, including the crucial heated oxygen sensor. If these monitors haven’t completed their tests, they show as “Incomplete,” and California regulations limit the number of incomplete monitors allowed for a passing smog test.
Specifically, the heated oxygen sensor monitor is vital for ensuring your car’s fuel efficiency and emissions are within acceptable limits. The heated oxygen sensor plays a critical role in measuring the oxygen content in the exhaust gas, allowing the engine control unit (ECU) to adjust the air-fuel mixture for optimal combustion. A properly functioning heated oxygen sensor is essential for reducing harmful pollutants.
So, how do you get these monitors, especially the heated oxygen sensor monitor, to complete and register as “OK”? The solution is performing an OBDII drive cycle. This is a specific driving pattern designed to trigger all the OBDII monitors to run and complete their tests. It’s not how you typically drive daily, which is why simply “driving it around” often doesn’t work.
Here’s a step-by-step OBDII drive cycle procedure, particularly effective for addressing the heated oxygen sensor monitor and other common incomplete monitors:
Important Notes Before You Start:
- Cold Start is Crucial: Begin with a cold start. The coolant temperature must be below 122°F (50°C), and the coolant and air temperature sensors should be within 11°F (6°C) of each other. Crucially, do not turn the ignition key to the “on” position before the cold start, as this can prevent the heated oxygen sensor diagnostic from running.
- Fuel Level: Ensure your fuel tank is between 1/4 and 3/4 full.
OBDII Drive Cycle Steps:
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Initial Idle (Oxygen Sensor Heater Test): Start the engine and immediately idle in drive (or neutral for manual transmissions) for two and a half minutes. Turn on the A/C and rear defrost. This step is designed to test the oxygen sensor heater circuits, along with the air pump and EVAP purge system.
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Moderate Acceleration (Misfire and Fuel Trim Test): Turn off the A/C and rear defrost. Accelerate smoothly to 55 mph (88 km/h) at half throttle. This initiates tests for ignition misfire, fuel trim, and canister purge.
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Steady Speed Cruise (Oxygen Sensor and EGR Test): Maintain a constant speed of 55 mph (88 km/h) for three minutes. This allows the OBDII system to monitor the EGR, air pump, oxygen sensors, and canister purge system.
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Deceleration (EGR and Purge Test): Coast down to 20 mph (32 km/h) without braking or depressing the clutch. This step checks EGR and purge functions during deceleration.
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Re-acceleration (Misfire and Fuel Trim Re-test): Accelerate again to 55 to 60 mph (88-96 km/h) at ¾ throttle. This re-evaluates misfire, fuel trim, and purge systems under a slightly higher load.
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Extended Cruise (Catalytic Converter and Oxygen Sensor Efficiency Test): Hold a steady speed of 55 to 60 mph (88-96 km/h) for five minutes. This is critical for monitoring catalytic converter efficiency, misfire, EGR, fuel trim, oxygen sensors, and purge functions over a longer period.
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Final Deceleration (EGR and Purge Final Check): Decelerate to a complete stop without braking. This performs a final check of the EGR and canister purge system.
After completing steps 1 through 4, you can check your OBDII monitor status using a scan tool. Many users, like the original poster, have found that after these initial steps, monitors like the oxygen sensor monitor and EGR monitor are often completed. A final check at a smog station can then confirm if you’ve successfully completed enough monitors to pass the smog test.
This OBDII drive cycle provides specific instructions to exercise your vehicle’s emission systems, particularly the heated oxygen sensor, in a way that normal driving often doesn’t. By following these steps, you can significantly increase your chances of completing the necessary monitors and passing your California smog test, getting you back on the road legally and with peace of mind.
