Review on Autel MS309 Universal OBD2 Scanner: Engine Fault Code Reader for Clearing Codes, Viewing Freeze Frame Data, and Completing I/M Readiness Smog Check by Nick Moo

Not for professionals or enthusiasts. Basically a first step tool to measure how engaged you are. The Autel AL301 has several unassigned codes that may appear as "B2aaa". This is a placeholder value (e.g. -9999), not real code. It should have been renamed as "N/A" or "Unknown" like its MS300 sister product. Many of these B2aaa appear in European vehicles when the CAN-BUS is not ready or reading out of sync. Disconnect, stop engine, reconnect, turn on battery, turn on engine, read again. Typically, "unknown" errors are additional errors derived from the main error. The good news is that for the underlying fault, you can usually find vehicle-specific solutions online that will fix the 'unknown' faults - but no guarantees. This is just a guide to which workshop to take your car to. It comes with a DTC Library CD, but it's Windows only and won't work in Wine on a Mac (you can use a virtual machine like Fusion or Parallels) - don't download the CD. **UPDATE** YES, it clears "saved" DTCs. It will not clear "current" DTCs if there is still something wrong with your vehicle (CEL will come back within a few drives). After you repair the car, you can try again to clear the codes. Some vehicles require the ignition to be in the ON or ACC position. Other vehicles require the engine to idle until the temperature rises. It all depends on how the car's on-board computer behaves. For example, on a 2008-2010 Cayenne, the code must be read with the engine running. To clear the stored codes the engine had to be idling, read the OBD, turn off the engine, then immediately switch back to ACC (but the engine is off) then the clear command was sent.