go for a longish test drive so the car gets up to temperature, if its low on fuel offer to stick in a few litres, that's the normal excuse for only letting you go round the block, or take a fuel container with you and top it up!!
Cheaper to put in a bit of fuel than to find there is a problem with the CHG.
I always think you can tell as soon as you drive the car, if its OK or not.
Good Luck with it.
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