Volkswagen Is Ordered to Recall Nearly 500k Vehicles Over Emissions Software

Personally I like internal egr because external egr systems have a tendency to clog in either the passageways or the solenoid controlled valve. EGR valve sticking is a common cause of cars stalling when slowing to a stop after cruising at medium-high speed. And even without the stalling egr is a common cause for check engine lights and smog test failures.

As for EGR monitoring, most OBD2 systems I've seen monitor the presence of the egr solenoid by looking for the back emf. So you'd need an inductor or a solenoid for that. Additionally, they usually will often do a test of the manifold pressure while cycling the valve, to confirm the flow rate (obviously this can only be done of the engine in question has a MAP sensor). And if the MAP sensor is the primary sensor for doing fuel monitoring (ie, no MAF sensor), then there would be no easy way of defeating this monitor without messing up the normal performance of the engine. So in my experience, defeating EGR and passing the EGR related OBD2 monitors is non trivial. But then, since there is usually an allowance (in the current CA smog check schemes) for some of the monitors to not have completed running while still passing the test, it doesn't matter too much in practice (can't disconnect the EGR valve, but the egr readiness monitor is moot). The EGR monitor is usually the last one to run anyway, so this makes passing the smog check with what would otherwise be a egr related OBD2 failure, fairly easy.

Beating O2 monitors is actually much more difficult in practice. First of all, an increasing number of O2 sensors in cars are wideband sensors which don't output the traditional switching signal one could simulate with a 555. Even some older cars use wideband O2 sensors (I have personal experience with two MY 1998 Toyotas [california cars] for which this is the case). Secondly, even if you do have all narrowband O2 sensors on a car, the way the O2 monitors work is that the downstream (of the catalyst) O2 sensor(s) output is compared to the upstream (of the catalyst) O2 sensor(s) to see, not whether the O2 sensor is working, but that the catalyst efficiency is above some threshold. Simply simulating one or both signals with a naive switching circuit will trip the catalyst efficiency monitor. And why would you want to disable the upstream O2 sensor(s) anyway, it's main job is to provide an error signal to the fuel system which would otherwise be a completely open loop system? Without a working feedback loop your fuel system won't be running very well, and usually falls back to a super conservative fuel mapping because of the danger of unknowingly running lean (obviously a concern for gas engines only, not diesels).

Defeating OBD2 monitoring in these sorts of ways is not an issue in any meaningful sense. Enthusiasts often will replace their ECUs wholesale with an aftermarket one. When the ecu hardware and its programming is completely outside of the manufacturer's control, who can say anything about the validity of it's outputs for emissions compliance purposes?

   General Motors agreed to pay $900 million as
   part of a Justice Department investigation
   into its failure to fix a deadly ignition
   switch defect blamed for more than 120 deaths.

I commuted to work in San Francisco on literbikes, but on weekends I would head south and open them up.