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Forum > General Smog Check > Question

1998 Jeep Cherokee Laredo Emission Monitors Incomplete

I have a 1998 Jeep Cherokee Laredo with 176,000 miles on it that has to be tested by a test only shop. Last year (2011) it passed ok but this year when I took it in to my favorite repair shop for a pre-test and they told me there were no reading stored in the computer and asked if the battery had gone dead. Well it had recently gotten so low I couldn't start the engine and they said that was the reason and I need to drive the vehicle starting with a cold engine and taking it immediately up to about 55 MPH before it warmed up and drive for about 50 miles to restore the readings. Is this true?? I'm handicapped and have no one to help me do this so this is an extreme hardship. 50 miles will be very difficult for me to be able to do without extreme pain so I wanted to find out if this is all correct. Thank you!


Answer:

Your Jeep Cherokee must perform a Drive Cycle in order to self-test it's emission components. While  your Jeep's battery was low it erased important emission monitors (also known as readiness flags). In order to set the required Monitors you must drive your Jeep for at least 100 miles, that's usually about a 2 week period.

Take extra caution while performing drive cycles on public roadways. Drive cycles can be difficult to follow under normal driving conditions. Insure you begin the Drive Cycle in the morning when your Jeep Cherokee is cool.

The Following is Standard OBD II Drive Cycle required to set all emission monitors, including the EVAP monitor, O2 monitor and CAT monitor.


Begin by:


- Start the engine. Idle the engine in drive for two and a half minutes with the A/C and rear defroster on.


- Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle.


- Hold at a steady speed of 55 mph for three minutes.


- Decelerate (coast down) to 20 mph without braking or depressing the clutch.


- Accelerate back to 55 to 60 mph at ¾ throttle.


- Hold at a steady speed of 55 to 60 mph for five minutes.


- Decelerate (coast down) to a stop without braking.


If all other emissions systems are functioning properly, completing the drive cycle above will set the "readiness flags" required to pass the smog check. It will not hurt to perform the drive cycle 2 or 3 times before the smog inspection.


posted by SmogTips Support

 

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