Smog test: Vehicle failed the MIL/Check Engine Light due to failure to successfully complete all OBD self tests
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From: Scott Dorsey on 15 May 2010 13:44 Kruse <kruse(a)kansas.net> wrote: >On May 15, 6:42=A0am, "Jeff Strickland" <crwlrj...(a)yahoo.com> wrote: > >> If you found plain old leaded Regular, or leaded >> Premium, and put it in your car, this will destroy a CAT. Bottom line is, >> you either have a bad CAT or a bad sensor. > >On a cross-country trip, where would he find regular leaded or leaded >premium? >Tetra ethyl lead was phased out YEARS ago. Out here we have a couple places that sell it for farm vehicles. Not legal for road use. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis."
From: Jeff Strickland on 15 May 2010 17:35 "Kruse" <kruse(a)kansas.net> wrote in message news:343c92da-e3a9-4b60-be98-5c23246d40db(a)o1g2000vbe.googlegroups.com... On May 15, 6:42 am, "Jeff Strickland" <crwlrj...(a)yahoo.com> wrote: > If you found plain old leaded Regular, or leaded > Premium, and put it in your car, this will destroy a CAT. Bottom line is, > you either have a bad CAT or a bad sensor. On a cross-country trip, where would he find regular leaded or leaded premium? Tetra ethyl lead was phased out YEARS ago. <JS> The point is, your car demands UNLEADED. Some of the farming communities might make leaded gas available for tractors. You shouldn't be able to even put the pump nozzle in the car, so this is a very remote thing to consider. But consider it, then toss it aside. If you can remember a time that the nozzle didn't fit well into the filler hole, that's a clue that maybe you got leaded gas. I agree though that it's not a likely thing to have happened.
From: Ray O on 16 May 2010 21:04 <condor_222(a)yahoo.com> wrote in message news:735e72ef-774f-4087-b171-6bd7232609ad(a)j36g2000prj.googlegroups.com... > Dear Experts, > > I've had some more adventures with my 99 Lexus ES300. > Now, about 107K miles. > > I had the alternator changed in the winter. > > Some weeks later, I was driving cross country. > I got a check engine light. > > I checked the code. It was the P0420, > Catalyst System Efficiency Below Threshold (Bank 1) > > > I pulled out my OBD tool, and erased it. > But It came back again a few times. > Sometimes, it took only about 40 miles. > Another time, it took 200 miles. > I probably got the code, and erased it at least 4 times. > > It only happened when I was driving cross country, all day long. > Since I returned to the city, I have not got the code. > > Today, I went to go get a smog check in California. > > Before I left, I connected the OBD to my laptop, and erasad all codes, > just to be sure. > > When I went for the smog test, everything was fine, except I failed: > > Vehicle failed the MIL/Check Engine Light due to failure to > successfully complete all OBD self tests. > > > I've since been reading more about the OBD here: > http://www.smogtips.com/functional_inspection.cfm > > One possibility I read there: > > Step D. Drive your vehicle for one week under normal driving > conditions. During this period the emissions computer is gathering > data and re-learning your vehicle's emissions components and systems. > The emissions computer OBDII (on-board diagnostics) system must > complete at least one drive cycle (in some cases two or three). A > drive cycle is a sequence of internal tests which the emissions > computer runs while your vehicle is being driven. This insures all > emissions systems are functioning properly. Proper "readiness flags" > are set as the computer completes it's cycles. Test cycles are unique > to a vehicle. Certain cycles run under very strict parameters, and may > require extended driving time to trigger on. Cycle data and readiness > flag information is available through your dealership's service > department. The data vary widely. > > > My questions. > > 1) Does Step D make sense, given that I'd erased the codes? If I > do drive the car for a few days like this, should I be able to pass > the test? > > 2) If I erased all the codes, are they really all erased? Or, is > there still some log about them? That they were there, I erased them, > and they are just flagged inactive now? > > > Thanks a lot! > > Yes, Step D makes sense because some diagnostic trouble codes (DTC's) have what is know as 2-trip detection logic. The explanation you posted gives a good explanation of how the computer defines a "trip.' The reason that some DTC's have 2-trip detection logic is to reduce the likelihood of false positive troubles. For DTC's with 2-trip detection logic, the computer (electronic control module or ECM) has to see at least 2 consecutive "trips' with no faults before it registers as "ready." If it sees a fault on one trip, it will store a pending code but won't illuminate the malfunction indicator light (DTC, commonly referred to as a check engine light). When you erased the codes, the ECM no longer had 2 good trips to show that it was "ready" for a test. As far as P0420, the ECM compares the signal from the sensor before the cat with the signal from the sensor after the cat. Basically, the signal from the pre-cat sensor should fluctuate within a certain voltage range as the ECM adjusts the air-fuel mixture, while the signal from the post-cat sensor should fluctuate less if the cat has done its job. If the post-cat signal resembles the pre-cat sensor, it means that the cat has not had sufficient effect on the oxygen content in the exhaust stream so the ECM illuminates the MIL and stores P0420. To properly diagnose P0420, you should check the signal from the post cat sensor. When you erased the codes, you really erased them and they are not stored in the ECM. It is generally not a good idea to clear codes and waiting to see if they come up again because the codes almost always re-appear and the ECM has to go through a readiness check again. With on-board diagnostic systems, there are very few false positives. In my former position with an automaker dealing with over 100 dealership service departments, I used to hear about and deal with oddball problems, and I can't remember ever running across a false positive DTC. -- Ray O (correct punctuation to reply)
From: condor_222 on 17 May 2010 17:32
Thanks everyone for all your replies! I drove the car a number of times over the weekend, and today it passed the test. As for the ethanol, now that you mention it, yes, I did fill up with ethanol blends along the way. Now that I am back in CA, I don't recall filling up with them. Good one! > I'm not certain, but I'd like to throw this out for consideration. > > On your cross country trip, did you fill the tank with E85 -- that's > gasoline that's 85% ethanol? I'm not sure, but maybe 85% ethanol is a > problem for the CAT. If you found plain old leaded Regular, or leaded > Premium, and put it in your car, this will destroy a CAT. Bottom line is, > you either have a bad CAT or a bad sensor. |