OBD2 emulator? Is there a way around emissions testing?

[boostjunkie]

A friend of mine has an upcoming emissions testing down here and is showing a CE light. I'm not sure of the specifics with the error code, but he was wondeing whether there was any way to make an OBD2 emulator that basically told the computer at the testing station that everything is ok. Does anyone know the specifics of what these testing stations actually reference when they hook up their scan tool? Are they basically just reading whether the light is illuminated without any engine data or do they download all of the engine data along with the code?

[ciper]

Find which code it is. It would be easier to emulate a failed sensor than the entire computer. Its probably something dumb like the knock sensor or purge valve.

[vrg3]

Yeah, I agree with ciper. It'd be simpler to make the CEL go away. Depending on the problem it might be cheap to fix correctly too.

I don't think it's feasible to emulate a functioning OBD-II engine management system. The OBD-II communications protocol is freakin' complicated. And I think they do scan more than just error codes; people with WRXes using MIL eliminators have failed emissions tests because the ECU hadn't seen the rear oxygen sensor go through enough cycles or something.

It might be worth asking an emissions inspection station what they do if a car's OBD-II port is broken or something; apparently in some states they just do a dyno test in that situation. You could disconnect the OBD-II port connector and the check engine light.

[boostjunkie]

Well, my friend has a 96 m3 and is swapping in a euro-spec m3 engine, which is obd1.

What I was thinking was to rig up a circuit to the coolant temp sensor to force the engine to be run in open loop mode, thereby negating several of the more "complicated" sensor emulations: o2 sensor, egr, etc.

Any thoughts?

[vrg3]

Oh, okay -- he's using the OBD-II ECU to run his Euro-spec engine?

And it's throwing a CEL...

Well, here's the thing. OBD-II systems include "readiness monitors." If the ECU doesn't know a sensor is missing or malfunctioning, but also doesn't know for certain that it's working, then it trips a flag. So, if the ECU was just reset but it hasn't had a chance to run closed-loop, then it might have a lambda readiness monitor flag set. If MD checks these readiness monitors, they may send your friend out for a drive before they'll test his car.

Also realize that an ECU will often notice a missing sensor even if it hasn't had a chance to use it. Like it will notice if there is no oxygen sensor heater, even if it doesn't care/know about the missing sensor element itself.

He should find out what the codes are; some AutoZones will scan them for free (call them up to find out which ones). Then we'll have a better idea how to proceed.

[EJ22TGC8]

if you want to make a unit that gives false readings then figure out what codes mean what. The OBDII system sends out binary codes that the emissions place reads. The binary codes tell whats wrong with the car as well as rpm and such. You could possably replicate the no error codes but the the variables such as rpm wouldn't come out right. I've been trying to figure a way around odbII for a while but no luck yet. I've talked to a couple of engineers that I know and they are helping me try to work some stuff out. I'll let you know if there are any breakthroughs.