I didn't pass emissions test because my service.

When the Check Engine light turns on it means the Engine Computer detected a problem and set a diagnostic fault code. Oil leaks are not monitored so you can rule that out. By the way, intake manifold leaks are very common on GM trucks and are normally the first thing suspected. The problem is the oil can run down onto and around the oil pan making it look like that's what's leaking. Brake system repairs and fluid flushes are not emissions-related either.

The first thing that needed to be done was to read the fault code(s). They indicate the circuit or system that needs further diagnosis. Now that the light is on again, the code has set again because the cause wasn't addressed during the original diagnosis. To be fair, if the charcoal canister was referenced in the code, the mechanic could think it was solved since the light didn't turn back on right after the repairs. The Engine Computer may only run self tests on the system and look for certain defects at specific times. You have to meet certain conditions while driving for those tests to run. That would result in the code setting days or weeks later.