Request for diagnostic advice to pinpoint least expensive solution to resolve persistent P0421 OBDII DTC

Permanent plonk! (the fact such creepy disgusting people exist is scary)

Moving forward, I found this Mitsubishi emissions recall bulletin titled: o Catalytic converter overheating - emissions recall campaign o EMR-05-001REVII, December 2005, Model 2002-05 Lancer

Purpose: Some affected vehicles have incorrect parameters in the Powertrain Control Module (PCM) software that may cause teh warm-up catalytic converter to overheat and melt when the vehicle is repeatedly driven at wide-open throttle. o For all affected vehicles, reprogram the PCM as described in this bulletin, regardless of the age or mileage of the vehicle. o If an affected vehicle has a Service Engine Soon (SES) lamp on and DTC P0421 set, also replace the warm-up catalytic converter, using an exhaust manifold repair kit.

Affected vehicles:

Customer notification: A letter will be sent to all owners of affected vehicles, telling them to bring their vehicle to a Mitsubishi Motors dealer to have the PCM reprogrammed at no change, and that if their vehicle has a SES lamp on for failure of the warm-up catalytic converter (DTC P0421), they will also receive a new warm-up catalytic converter.

In addition, owners will be advised that the new warranty coverage for the warm-up catalytic converter will be extended from 8 years/80,000 miles to a limit of 8 years/100,000 miles. Until February 28, 2006, replacement of the warm-up catalytic converter will be free of charge, regardless of vehicle mileage.

After February 28, 206, all owners (regardless of vehicle mileage) will be entitled to the PCM reflash free of charge. However, warm-up catalytic converter replacement will not be covered under the warranty if a 2004-2005 model has over 80,000 miles. o P/N MN195802 Lancer 2.0L, 2004, Exhaust Manifold Repair Kit (includes manifold with catalytic converter, gasket, and nuts)

Drat.

The recall was already performed; but they didn't replace the warmup cat. o All the dealer did was reflash the PCM (i.e., P0421 didn't come up then).

Just in case, this appears to be the $400 + $40 tax recall parts: o P/N MN195802 Lancer 2.0L, 2004, Exhaust Manifold Repair Kit

I'm not sure yet if there are two cats, but it appears the car may have o A warmup cat, plus, o A regular cat

Since this recall talks only about the "warmup cat" melting due to a poorly coded PCM (which they reflashed, apparently, as per EMR-05-001REVII TSB).

Oh I love it when you plonk me, plonk me again and again you beast of a man

Youse my hero arlen, you no all about internet

Update: o

Aghast, I happened to use the dejagoogle feature to look at the a.h.r newsgroup, which, much to my chagrin, is more than 99.9% worthless spam. o

Given the lack of value in a.h.r, I will no longer be posting the results of this thread to that newsgroup, preferring to put the updates on r.a.t which, thankfully, isn't almost 100% worthless spam as a.h.r clearly is.

I'll also drop ca.driving, such that this is the only worthwhile ng: o Request for diagnostic advice to pinpoint least expensive solution to resolve persistent P0421 OBDII DTC

BTW, the vehicle passed smog today; but that doesn't solve the problem of diagnostics since it only made it through the intermittent window.

Weeze gonna miss you ya no it all arrogant prick. You may have been trolled but not spammed but yoose to dum to no the difrince yu is.

On Tue, 17 Nov 2020 23:06:39 -0000 (UTC), Arlen Holder posted for all of us to digest...

Here you go. As always check electrical connections.

By the way your scanner is not giving you live data that you can can use. You need something more advanced. You don't need the "cheapest" fix-you need the "correct" fix and shooting the parts cannon at it doesn't work.

It sounds like the issue is borderline, IE the cat isn't really dead but under colder temps it takes longer to warm up and sets the code.

The downstream sensor is the one used for this testing, the lambda sensor upstream isn't really involved in the test other than to verify that the mix going into the cat is correct.

Yep, Steady state isn't the real item it tests though, what the test looks for is how long does the cat take to start working and lower the levels going to the downstream sensor.

That is the trick in testing, the easiest way is to use a 5 gas analyzer and watch the numbers as the cat ignites, but not everyone has one. The next is to measure the sensor output directly and see when it actually shows a change. Just remember that it only uses the downstream sensor for this test.