GMC Troubleshooting Questions? Ask a Mechanic for Answers
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There are several criteria for the vehicle to run the monitor. The fuel tank must be between 1/4 and 3/4 full and set for 8 hours prior to being driven then it must be driven 45-55MPH for 20 minutes. If it sees any criteria not met it will not run the monitor.
yes it has to be continuous. no stopping
I would have to see some scan data. It obviously is seeing a leak or the fuel tank pressure is not sufficient for the test.