Help! Check Engine p0161 p0305 p0420

[Yukulele]

My Check engine like came on the day i bought this truck (about 3-4 months ago). Got the code scanned and received p0420 which is catalyst under threshold bank 1. So i figured it was the 02 sensor since the truck runs mint and has plenty of power. Replaced the 02 sensor last week and check engine light never went off. Today i was driving and the check engine started blinking. I brought it back to auto zone and today it scanned with p0420 still, as well as P0305 which is misfire in cylinder 5, and p0161 which is oxygen sensor bank 2 sensor 2 which is the other exhaust, not the one with the bad supposedly bad cat.

So i am guessing i am going to replace the cat since it may be bad because the heat shield around it rattles and is rotted, maybe its getting really hot, doesn't turn red though. But the truck runs mint, i would never think it was misfiring you cant even hear it running its so smooth and the idle is dead on.
Im stumped, please help!

-Mike

 

[piranah]

When the engine light blinks it means abandon ship.

The engine is toast. might sound fine but there is a ghost in there you will never get rid of...had this same exact issue on three other GM cars.

 

[SunlitComet]

Your CEL will blink anytime a misfire is detected meaning fix ASAP or you will cause more damage.

For p0161 the heater element in the O2 sensor in the right cylinder bank downstream of the converter has probably burned out for good.

For p0305 you need to find out if your ignition, injector or something is at fualt.

The p0420 has to do with lack of converter efficiency. But absolutely fix the misfire first. Have autozone clear your codes and take a few trips to see what happens.

If you still get codes about converter efficiency and if you have eliminated sensor as the cause you should probably replace them or you will probably fail a smog test and the light will stay on so you wont know if something else is wrong later.

For a 96 tahoe like my own magnaflow sells a direct fit dual converter assy. that bolts in. Three of the four O2 sensors go into this assy..

Your p0161 coded sensor is the one attached to pipe downstream of the converter assy mounting flange if it is like mine.

 

[Yukulele]

When the engine light blinks it means abandon ship.

The engine is toast. might sound fine but there is a ghost in there you will never get rid of...had this same exact issue on three other GM cars.

Yeah okay guy, I have 1998 oldsmobile intrigue that had a blinking check engine light and it was missing, needed new wires now its fine...

Your CEL will blink anytime a misfire is detected meaning fix ASAP or you will cause more damage.

For p0161 the heater element in the O2 sensor in the right cylinder bank downstream of the converter has probably burned out for good.

For p0305 you need to find out if your ignition, injector or something is at fualt.

The p0420 has to do with lack of converter efficiency. But absolutely fix the misfire first. Have autozone clear your codes and take a few trips to see what happens.

If you still get codes about converter efficiency and if you have eliminated sensor as the cause you should probably replace them or you will probably fail a smog test and the light will stay on so you wont know if something else is wrong later.

For a 96 tahoe like my own magnaflow sells a direct fit dual converter assy. that bolts in. Three of the four O2 sensors go into this assy..

Your p0161 coded sensor is the one attached to pipe downstream of the converter assy mounting flange if it is like mine.

Thank you for your input, I think the cat needs to go cuz today i was hitting it with my hand and it was rattling inside. Also i was driving it today and smelt the dreaded sulfur smell. Once i fix that i am going to reset the codes and see what happens from there. I know for sure this truck isnt missing. This may sound stupid but maybe from the increased back pressure on the drivers side bank it caused the missfire in cylinder 5, i dont know. I also just changed the o2 sensor after the cat on bank 1. but the p0305 code is for bank 2.
Fortunatly this truck does not get tested for smog because it is OBDII Although it should be fixed and again fortunate that i have another truck i can drive in the mean time.

Also i was thinking if i should just clamp a new cat on there cuz i dont have a welder, something like this http://www.rockauto.com/catalog/moreinfo.php?pk=1516118 for $70. Or get that whole bolt on system like this http://www.rockauto.com/catalog/moreinfo.php?pk=1317556 for $267

Thanks
-Mike

 

[SunlitComet]

If your converter is rattling inside then replace it. I highly recommend the direct fit. If you replaced the p0420 coded sensor for left(#1) bank(cyl 1-3-5-7) and still get a p0420 after reset then means that converter is about dead. Usually the missing is most noticable happening at idle. Your p0305 misfire on #5 should be on bank one. If you are shure you have replace the sensor for bank one and still get a 90420 code then replace your converter assy with a direct fit and replace you post verter O2 located just aft of the mounting flange of the converter assy between that flange and the muffler. That should get rid of the p0161 heater fualt in bank 2.

I am assuming your truck is layed out like mine which has the pipes cross over before rentering the converters.

What is your model year and engine size to be sure?

I am planing to change over to the magna's my self later on. The whole converter assy. will cost about $550 and I plan to change to edelbrock shorty headers and flowmaster cat back exhuast as well. All will be a direct bolt on so I could do it in stages. About $1300 for all of it from summitracing.

Some pictures below so you can see where three of the sensors go. The one on the muffler assy is not visible.

All california legal too.

Mine is OBD2 as well but I still need to have a smog every two years even though it was a federal emmisions class to start with. What state are you in?

 

[Yukulele]

If your converter is rattling inside then replace it. I highly recommend the direct fit. If you replaced the p0420 coded sensor for left(#1) bank(cyl 1-3-5-7) and still get a p0420 after reset then means that converter is about dead. Usually the missing is most noticable happening at idle. Your p0305 misfire on #5 should be on bank one. If you are shure you have replace the sensor for bank one and still get a 90420 code then replace your converter assy with a direct fit and replace you post verter O2 located just aft of the mounting flange of the converter assy between that flange and the muffler. That should get rid of the p0161 heater fualt in bank 2.

I am assuming your truck is layed out like mine which has the pipes cross over before rentering the converters.

What is your model year and engine size to be sure?

I am planing to change over to the magna's my self later on. The whole converter assy. will cost about $550 and I plan to change to edelbrock shorty headers and flowmaster cat back exhuast as well. All will be a direct bolt on so I could do it in stages. About $1300 for all of it from summitracing.

Some pictures below so you can see where three of the sensors go. The one on the muffler assy is not visible.

All california legal too.

Mine is OBD2 as well but I still need to have a smog every two years even though it was a federal emmisions class to start with. What state are you in?

First things first, thank you so much for your input there are alot of helpful people up here on this forum.

Second off I live in New York and its a 1998 4 door Yukon with the 5.7 engine. I was looking under it today again and i think i will be best off replacing the bolt in system because cutting, clamping, jerry welding with a 110 arc just inst going to cut it. Although do you think those flange bolts are going to be tough? I do have access to an impact wrench and i have taken head bolts off before in the past but i guess it all depends on the condition. I am not looking for any performance upgrades, that money gets dumped into my jeep . But your setup sounds like it will be nice.

Also i am sure that i replaced the o2 sensor for bank 1 sensor 2 location. Do you think the p0305 miss in cylinder 5 is from the cat? and it also seems strange that the p0161 code from bank 2 sensor 2 would just so randomly happen but i guess that's just how these things go

Thanks
-Mike

 

[SunlitComet]

I believe the front flanges of assy. fit over studs in the manifolds so I would say it might be less likely you would break a stud as opposed to wrenching directly on a bolt head. I would not try an impact just yet. Try some penetrating oil first and maybe try tightening a few degrees before loosing and when you do get them loose if they start to snag hit reverse again. It always a tricky with hardware around exhaust components.

If performance oriented you are not, stick with that assy. you showed earlier as long as the build quality is good.

Chase all the threads you can and use some anti-sieze with new nuts. New gaskets of course.

I think random is likely if there are no other heater faults but you are always left wondering since it is in the same system.

My own vehicle I just got came with a malfunctioning injectors 5&7, MAF sensor, one 02 sensor with a heater fault, misfiring issues and if I believe a shop small compression leak on the same cylinders. I have done the maf sensor and have a new 02 but will wait to replace the incjector assy. with the improved type(there is a TSB on this covering years 96-02)

Have you examined the #5 plug and compared to another? I think #5 may have been contributing to the problem in the form of converter contamination or overheating(btw, a converter should never glow). The misfire detection is done by measuring rotational velocity differences using the crankshaft position sensor. Misfires can affect your converter but I weak converter shouldn't misfire one cylinder, usually a whole bank would be affected by buildup of back pressure.

I pulled number five on mine and it just has light oil residue. I don't suspect gasket damage yet as much I think the injector is just not working as to burn any fuel otherwise it should look different. At this point I think it is just typical oil residue that just has no fuel to burn it off. I have not pulled #7 yet. I will rexamine the issue once I replace everything.Unfortunately lack of funds is stalling progress.

When you are done and clear your codes just keep an I eye on the CEL light if it blinks that is a misfire detection.

 

[gojrracing]

Hi mike, thanks for the information in this thread. I hope that you can resolve your issues.

 

[ravingmadman]

What was the resolution, if any? I've got the P0420 with P0305 as well. I already replaced both up and downstream O2 sensors on the driver's side (before reading this), but I've still got the misfire. When I pull the plug, it's dry, identical to the others on the same side of the engine. I have a spark plug wire induction tester, and it shows good spark. I was thinking it was the injectors, but it doesn't feel right. If this were a timing issue, I'd expect to see other codes in addition. What am I missing?

 

[ravingmadman]

Ok. So after talking to my buddies, who are more intelligent than I, they say that the codes for the misfire and converter aren't related, though the misfire could cause the converter to go, if unattended for long enough, but that's not the case. So, I'm off to fix a misfire, then replace the cats. Yay.