On the 2010 Chevy Tahoe, when the Tighten Gas Cap message comes on AND there is a Check Engine Light also on, this means there is a problem somewhere in the EVAP (emissions control/recovery) System. First, make sure the replacement fuel cap meets GM specs. Most aftermarket caps will not meet specs. If you are certain the cap is good, then the next thing to do is to have the Diagnostic Trouble Codes (aka “P-Codes”) scanned from the on-board computer. Unfortunately, there are literally dozens of parts and sensors in the EVAP System, so without those p-codes, there’s no way to say for sure where the problem lies. These p-codes will point to the faulty part/sensor and from there, we can then make the correct diagnosis and repair. You can have these p-codes read FREE (except in California) at any local “big chain” part store (ie. AutoZone, PepBoys, Advanced, etc).
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