09-30-2021, 07:23 AM
They used to use the sniffers up the tailpipe here a long time ago, but for most cars that are on the road now they just plug into the ODBII port and get everything from the vehicle sensors. From what I have read online (disclaimer: I am certainly no expert here) I think that’s more accurate since the car can report much more than just what spits out in the exhaust since it can collect timing, fuel to air ratios as well as O2 and catalytic sensor data.
The downside of relying on what the car tells them rather than a real world sample is that you can now game the results through dodgy programming like Volkswagen did with their diesel engine ECU’s. If I recall, their programming would detect when a diagnostic computer was connected to the ODBII port and change the way the engine ran in order to meet emissions requirements. Once unplugged they reverted back to the optimal VW configuration that caused a lot more pollution. Makes me wonder how many other car makers are doing that but haven’t been caught yet.
The downside of relying on what the car tells them rather than a real world sample is that you can now game the results through dodgy programming like Volkswagen did with their diesel engine ECU’s. If I recall, their programming would detect when a diagnostic computer was connected to the ODBII port and change the way the engine ran in order to meet emissions requirements. Once unplugged they reverted back to the optimal VW configuration that caused a lot more pollution. Makes me wonder how many other car makers are doing that but haven’t been caught yet.