Every month or so I recieve a PM asking me about this thread so I'm going to update it to answer the question I get in every one of these PM's.
Before you freak out and think your content may be off it can be checked. You will probably have to pay for this but it much cheaper than doing the initial relearn. I charge a half hour for this but I would under no circumstances expect to pay more than an hour of diagnostic time to just check the content. If repairs are necessary expect the price to climb substantially. I don't know if many aftermarket facilities have the necessary tools but every GM dealer should have them, they are manditory tools for every dealer. The dealer has a special tool that a fuel sample from your vehicle is poured into. A very low voltage is pulsed through the tool and an A/C frequency reading is taken from the tool. The frequency measured translates into an actual fuel alcohol content. Then we hook up the scan tool and look at the data list to see what the calculated fuel content is. If it is within 10% there would be no action required, you would not need to relearn anything.
If the calculated content is not withinn 10% an initial fueling event would need to be performed. This is not something that can be done at home. First the tank needs to be drained and dried, this is pretty difficult at home. But the thing that makes it reall not a diy event is that you will need the bi-directional scan tool to force the composition reset, not many of us have a $2,500 scan tool sitting in the garage. These are the steps we take to do the initial relearn event.
- Drain the fuel tank.
- A complete key cycle needs to occur when the fuel tank is drained to ensure the ECM/PCM recognizes a refueling event.
- Key ON, engine OFF with drained fuel tank.
- Key OFF, add at least 11 L (3 gal) of non-blended gasoline to the fuel tank.
- Perform the Fuel Composition Reset using a scan tool.
Ok time for good news bad news. GM has released revised calibrations for some FlexFuel (E85 compatible) vehicles that will accept the introduction of gasoline/ethanol blended fuels with ANY ethanol concentration that falls between 0 and 85%. What does that mean to you, many of these vehicles have a recall to cover this new calibration and part of that recall is checking the content and adjusting it as necessary, all covered under the recall. To find out if your vehicle is covered contact your dealer with your VIN and current miles on the vehicle. You will still need to go by the refueling guidelines after the reflash it is just so the vehicle will accept fuel between 0-85% where before the reflash it would only recognize fuels between 0-10% or 85-90%.
Bad news, if it does not fall under the recall and testing shows that the learned and actual content is not withinn spec it will not be covered under warranty. The warranty is to cover manufacturer defects, this is not a defect. There is a section in the manual on how to refuel your vehicle, it isn't GM's fault if you didn't read your manual to know how your vehicle works. The purpose of my original post was to emphasize the importance and to shed some light to the how's and why's of the system.
Edited by sparkstech, 14 March 2009 - 11:49 AM.
The tech who thinks he knows it all hasn't begun to learn.
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