Your readings are useless so you need to find out why. In all instances of useless tool information one needs a standard. The standard here is the key on engine off duty cycle. On a federal car it is 70% on a California car it is 85%. Verify that condition and we can go from there.

Also the instance of a fixed duty cycle is often a code. The codes can vary but are usually not for 100% duty cycle (figuring 97% rounded off) as a pegged mixture is also fixed at the end points. This is why one needs to calibrate ones test and why more info is needed such as the year model.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician