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#1
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I need help with OBD freeze frame data
I recently purchased an OBD-II auto scanner. I understand the basic
obd codes, but there is also this freeze frame data that is completely beyond me. It is stuff about short and long term fuel trim systems. What do those percentages mean and how can I use them effectively? |
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#2
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I need help with OBD freeze frame data
The simple answer is that your Freeze Frame Data is a 'saved' profile of all
your emissions/operating parameters (usually the MAP/MAF have greatest fuel authority then the EGR/O2 sensors) at the time the CEL code is generated. In otherwords, fuel trim percentages help troubleshoot drivability issues based on comparing sensor outputs from most of the 5V reference emissions sensors on your vehicle. If your short term fuel percentage shows +28, this means that your computer is adding 28% fuel to compensate for a lean condition (could be a bad O2 sensor, fuel leak, bad plug, EGR....). Looking at both fuel trims levels can help troubleshoot IF- THEN situations a little more clearly. Fuel Trim ratings simply allow us to measure whether fuel is being added or taken away from baseline fuel duty cycles. Short term is basically adjustments on-the-fly to fuel delivery and long term is factored as a result of 'x' amount of drivability cycles to give you a 'long term' average that might eliminate minor adjustments, etc.. As we all know, this is a half-asses explanation as there are many variables and speciific timing involved in the correct 'technical' answer so you would best be served by looking at something like this: http://www.asashop.org/autoinc/november/scantool.htm (MUCH better explanation). Take care, Andrew. in article , at wrote on 6/20/07 12:30 PM: > I recently purchased an OBD-II auto scanner. I understand the basic > obd codes, but there is also this freeze frame data that is completely > beyond me. It is stuff about short and long term fuel trim systems. > What do those percentages mean and how can I use them effectively? |
#4
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I need help with OBD freeze frame data
Mike Romain > wrote:
wrote: >> I recently purchased an OBD-II auto scanner. I understand the basic >> obd codes, but there is also this freeze frame data that is completely >> beyond me. It is stuff about short and long term fuel trim systems. >> What do those percentages mean and how can I use them effectively? > >Unless you have a specific problem, those scanners are totally useless >in my opinion. This is the case, though, for EVERY diagnostic tool ever made. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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