P0420 troubleshooting- Prius 2006

I would think you would want the sensors to be changing and scaling etc if not it'll code no? I've same issue exact scenario chasing same 2 yrs. Sensors are scaling .I have aftermarket cat but a known good made by big company.havent fooled with lately. Still 47 to 49 MPG.

 

If you're pulling 0 volts from upstream sensor, replacing that should resolve the problem as you'll throw P0420 if the upstream or downstream sensor is not working.

 

That's what I was wondering is is there specific codes for the upstream and or the downstream sensors because it's upstream is dead zero voltage and whatnot so I'm thinking that's kaput as in no good and that will also get him the '0420 code? So you'd get the 0420 code plus the bad up or downstream sensor or you get the bad up or downstream sensor but no 0420? Or can the '0420 have a subcode for the sensor Don't know right now I have the '0420 I don't think there's any subcodes I'll have to look again or if it's even subcode capable.

 

P0420 reports a failing result from a catalyst oxygen storage capacity test. The car runs the test once each time you drive and it takes 30 seconds to run. It works by running the engine deliberately too lean for some seconds, to let the catalyst soak up some extra oxygen, and then running deliberately rich for some seconds, to see how long before the downstream sensor sees the oxygen drop, which indicates how much the catalyst was able to store.

For the car to even run that test, the A/F (upstream) and O2 (downstream) sensors have to be working, as well as the MAF sensor, the coolant temperature sensor, and intake air temperature sensor, among others. The test is skipped if any of the codes P0011, P0012, P0031, P0032, P0037, P0038, P0100–P0103, P0115–P0118, P0120–P0123, P2135, P0125, P0136, P0171, P0172, P0300–P0304, P0335, P0340, P0341, P0351–P0354, P0442–P0456, P0500, P2196, or P2A00 are present.

Several of those codes report different problems with the A/F sensor (P0031, P0032, P2196, P2A00) or the O2 sensor (P0037, P0038, P0136).

A zero-volt signal from the A/F sensor should definitely produce a P2196 (given that the O2 sensor output is definitely not showing rich), and that ought to prevent the P0420 monitor from even running. I'm kind of surprised the O2 sensor value itself hasn't triggered a P0136 or P0137.

A couple of those codes seem to have a kind of first-detected-gets-shown relationship. If there's a P0136 showing, the P2196 monitor doesn't even run, and vice versa.

I wonder if that 0.00 A/F sensor voltage is for real, or maybe OBDLink doesn't have the right info for that PID? Has this OBDLink shown you a non-zero A/F sensor voltage in any other similar model-year Prius? I wonder what Techstream would show.

There is a funny note in the P2196 troubleshooting section saying that any OBD-II scan tool (other than the "intelligent tester", now read Techstream) will display "one fifth of the A/F sensor output" that Techstream would show. Sounds like they had a scaling coefficient off by a factor of five in data they published that other tools rely on, and Techstream has a correction baked in.

Still, five times zero's still zero, so I wonder if something more basic is wrong here.

 

I don't know about the "resistance" data - I have never used it to diagnose any faults. All I care about are the A/F - O2 sensor voltage readings and Fuel Trim numbers. If your scandata for the A/F sensor is incorrect, then anything related to that is also suspect.

Toyota upstream A/F sensor is displayed as a "voltage" on the scantool (it's actually a microamp current that changes based on detected exhaust gas mixture). At steady throttle conditions it should be "around" 3.3V. It goes lower (towards 2.0V) when the engine is "rich" (excess fuel- Lambda of under 1.0), and higher (up to 5.0V with fuel cutoff) when "lean"(excess O2- Lambda of over 1.0).

The downstream O2 sensor has a 0-1V output range. It should go over 0.9V when "rich" and under 0.1V when "lean".

Fuel Trim is the ECM adjusting fuel injection based on the A/F (and sometimes the O2) readings. If everything in the car is "perfect" and close to how it left the factory, then Fuel Trim should be close to 0% (+/- 5%). Short Term + Long Term = Total Fuel Trim.

Up to 10% is ok. 10-20% indicates that something is not right. Over 20+% will usually set codes. Prius seems to be a bit strange, as it will often set other "component" codes (such as MAF sensor) or have performance faults without setting any (expected) fuel trim codes.

Are you using OBDLink for the fuel injection volume control? I have that app and don't see any bidirectional commands or tests anywhere.



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Try it me thinks the cars testing sequence is at fault as it was design fault possibly . I had an AC Delco Corolla same for ten plus years Toyoda USA finally offered a AC Delco computer eProm update flash for 160 dollars would fix issue . Never paid for it as it should've been free still have that car today. My gen 2 Prius all are same p0420. No fix maybe a 3K original CAT . But no guarantee of that and you're stuck with the part and the prices you paid after it's done and it doesn't work so you lose both ways possibly where I am I have no admissions testing so I'm golden a lot of places have reverted to this just because of these antics

 

If you decide to replace the downstream sensor, I've had very good results with the DENSO 2344623 from RockAuto for $52.
I've used them in a dozen or so Gen 2s when needed following cat theft. I have yet to (personally) run across a Gen 2 that needed the upstream replaced.

 

As far as I know theyres no update for Prius e prom or any of it no hybrids dot test cat at startup . It's obviously not the thing to be doing. Apparently maybe different gen4 and up . Will see at some point. You should be able to get a rider for crap like this and can if you argue correctly . If a exhaust gas analyzer is clean or clear in spec . Than lights mean nothing . Engine mgmnt system is doing job pass! . Show me or is the dirty????. Exactly why counties all over America dropping emissions testing all over . Like my county realized the BS and dropped like hot potato. They didn't even bother to go back to analyzing. Because it's a rackett that we all saw through. Now is gone .

 

I had my cat stolen in NYC. I have had it replaced TWICE now, and still the dreaded P0420. I don't think my solution is to replace the cat because I know the second one was a california one. But my car cannot pass inspection because I currently live in NYC. And I would love some help if you have any ideas for me. I'm already past the due date, and they give tickets on the street for expired inspections. Thanks in advance.

 

What did you end up doing? I had the same thing happen, where the new cat was fine until I hit a bump! And now I can't pass inspection. DEfinitely a racket. I went to Mavis, and the guy says the sensors are "out of range". Trying to tell me I need to replace both sensors AND the cat! The mechanic who placed the cat, is not available, and I'm screwed because I can't inspect the car, and so can't drive.

 

Do you have a scan tool yourself that can show the Engine and ECT data list?

 

So do you mean you bottomed out on a speed bump?

Do mean that there is now a loud exhaust noise after hitting the bump?

 

A poor installation/seal at the exhaust manifold flange can create "false" P0420 codes. Cheap $15 ebay downstream O2 sensors can do the same.