When to Use Fuel Trim Data

Fuel trim value outside of prescribed operating range is not a problem in itself. This condition is typically an indication that other problems exist. Fuel trim data can help lead you to the cause of these problems. Typically you will use fuel trim data to:

• Perform a pre-diagnosis quick check of feedback control

• Troubleshoot the cause of emissions system failure (I/M test failures)

• Troubleshoot cause of driveability problems, particularly when these problems occur during open loop operating modes (i.e. starting, warm-up, power enrichment)

• Perform post-repair quick check of feedback control

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

Don't pay hundreds of dollars to find out what is wrong with your car. This book is dedicated to helping the do it yourself home and independent technician understand and use OBD-II technology to diagnose and repair their own vehicles.

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