O2 sensor heater
Team Owner
Joined: Sep 2001
Posts: 23,283
Likes: 906
From: Lake Elsinore, CA
Certain states allow 0,1 or even 2 "Not Ready" flags during an emissions test. The emissions test goes through a series of checks to make sure all of the relevant systems are operational. The oxygen sensors are one of the components tested - they depend on a heated element to be working in order to do their job properly. If you don't meet the minimum requirement of systems at the ready when they test, well, you fail.
If you have recently replaced your battery or disconnected it (or some similar activity) and not driven the car a sufficient time for all these systems to re-initialize, you can fail the test. To see if this is the problem, perfom the OBD II cycle listed below to get all the systems back in the ready mode. If this doesn't do it for you, check your computer codes to try and identify the problem. I use a tuning package, EFI Live to test the emissions readiness before going to the station for the test. (We no longer have emissions testing here in IN.)
Find a lonely highway to do this as it's a strange sequence of tasks to do with traffic around. I have gotten to the ready state without going through the entire sequence. Another option is to just wait, drive the car for a month or so normally, and everything should be in the green
Best of luck.
General Motors' OBD-II driving cycle
• Cold Start. In order to be classified as a cold start, the engine coolant temperature must be
below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at start-up. Do not
leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
• Idle. The engine must be run for two and a half minutes with the air conditioner on and rear
defroster on. The more electrical load you can apply the better. This will test the O2 heater,
Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
• Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until
88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics
will be performed.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time
the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
• Decelerate. Let off the accelerator pedal. Do not shift or touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
• Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same
diagnostics as in step 3.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be
performed. If the catalyst is marginal or the battery has been disconnected, it may take 5
complete driving cycles to determine the state of the catalyst.
• Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or
brakes or shift gears.
If you have recently replaced your battery or disconnected it (or some similar activity) and not driven the car a sufficient time for all these systems to re-initialize, you can fail the test. To see if this is the problem, perfom the OBD II cycle listed below to get all the systems back in the ready mode. If this doesn't do it for you, check your computer codes to try and identify the problem. I use a tuning package, EFI Live to test the emissions readiness before going to the station for the test. (We no longer have emissions testing here in IN.)
Find a lonely highway to do this as it's a strange sequence of tasks to do with traffic around. I have gotten to the ready state without going through the entire sequence. Another option is to just wait, drive the car for a month or so normally, and everything should be in the green
Best of luck.
General Motors' OBD-II driving cycle
• Cold Start. In order to be classified as a cold start, the engine coolant temperature must be
below 50°C (122°F) and within 6°C (11°F) of the ambient air temperature at start-up. Do not
leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
• Idle. The engine must be run for two and a half minutes with the air conditioner on and rear
defroster on. The more electrical load you can apply the better. This will test the O2 heater,
Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
• Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until
88km/hr (55mph) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics
will be performed.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for 3 minutes. During this time
the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
• Decelerate. Let off the accelerator pedal. Do not shift or touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 32km/hr (20 mph). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
• Accelerate. Accelerate at 3/4 throttle until 88-96 km/hr (55-60mph). This will perform the same
diagnostics as in step 3.
• Hold Steady Speed. Hold a steady speed of 88km/hr (55mph) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be
performed. If the catalyst is marginal or the battery has been disconnected, it may take 5
complete driving cycles to determine the state of the catalyst.
• Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or
brakes or shift gears.
