Help on scanned codes on my Sierra

Have a 05 Sierra with a 4.3 six that has become quite a disappointment to me. Bought it new, has 87,000 miles on it and it has serious rust issues.
Now I have to get it inspected with a pile of codes on it that I don't know what to do with them. Would appreciate any insight you are willing to lend.

Codes are: P0300, P0420, P0430, P0138, P0158, and P0171.

Only thing I know is there is a GM TSB on the distributor "vent" screens (I will yank them tomorrow, as per TSB, and install new OEM cap and rotor. Plugs and wires were changed about 10,000 miles ago. The last code - P0171 makes me wonder if the thermostat is the culprit since the truck seems to run cooler than it did when new. I just don't know.

Would appreciate any help you can give.

Thanks.
 
my o6 4.3 wt tossed similiar codes. check your 02 sensoers, the scanner should indicate which bank. bank 1 lt side, bank2 passenger side. my lt 02 sensor after the cat was bad. check for a blown fuse in the panel also. sometimes the fuse will pop too with a bad sensor. do you have a scan tool that can clear the codes?
 
Yes I cleared the codes. It has been running rough for quite some time. I am hoping after I change the cap and rotor, it might clear.
 
Just off the top of my head, the P0420 is a catalytic converter operating below efficiency threshold. P0171 and P0158 are mixture codes.

IMHO, with that many codes, you need to start with the FIRST code output, and solve that one, clear the rest, and drive it until the MIL light comes on again. Then repeat the procedure until all of the codes stop recurring. Usually, one problem starts, and ends up throwing things out of kilter until it generates a bunch more "bogus" codes.
Good luck.
 
PO300 = misfire not linked to just one cylinder.

You need to solve that code FIRST before even DREAMING about any codes pertaining to the exhaust oxygen sensors.

I agree with installing a new OEM cap and rotor, but don"t worry about ripping out the distributor vent screens just yet.

Get it running without a misfire, and THEN worry about doing PM to prevent the problem from returning.
 
P0171 would not generate from a thermostat problem, incidentally there are certain codes that can set due to engine temp/thermostat concerns, especially when they are stuck op and running too cool.

P0171 means the engine (bank 1) is running too lean, lean to the point where the PCM attempted to add extra fuel and reached its limit of compensation and its still too lean. Vacuum leaks (vac lines/hoses, intake gasket etc are usually the culprit but a fuel supply/delivery problem often cause problems too among a few other things.

The p0138,p0158 are for the rear oxygen sensors behind the catalytic converters (after cat) indicating excessive voltage. Possible causes are faulty cats, shorted/melted sensors or wiring.

The p0420,p0430 codes generate from the rear sensors too. These codes trip when the PCM sees the rear sensors mimicking the front sensor switch rate which means the cats are not cleaning the exhaust emissions to a specific level. Most likely cause is the catalytic converters. Often times driving a vehicle with excessive misfiring can burn out the cats from excessive heat generated from unburned fuel.

The p0300 is typical when an engine simply runs rough and not on a particular cylinder or random. Many things can cause this from typical tune up items, sensors-ignition, mechanical problems, fuel problems, sensors, among the same things listed above with p0171. Since you are taking the dist cap off, verify the rotor or dist shaft does not have excessive play when turning back/forth. I have seen a few of these trucks with worn gears on the dist, also some worn dist shafts too.

So, basically I would try to look into the P0171 and P0300 running problem first, the other codes maybe related to the running problem from these two codes.

Sorry for the long post, I dont want to add more right now but if you check some stuff out then repost and maybe we can help narrow things down.
 
qI just went thru the inspection problem with my 2004 Pontiac Bonneville with a 3.8L in NY state.You can have one error code as long as MIL light is not on. Refused to be held hostage by a repair shop. A ton of info on internet using google.
Your PO300 code is multiple misfire. PO304 would be the only the number 4 cylinder. I think you mentioned cap and wires. Everbody gets excited about the vent screens. But unless their plugged, or their is moisture under cap I just do not see the problem. I would go with maybe cap, wires(can be tested), and plugs. Then like another poster suggested drive it a while. I found also that one problem can start a cascade of false readings. But, if that is not your case,
PO420,PO430 is the catalytic converter. Probably most catalytic converters can be saved. They read underperforming or something to that effect.The catalytic converter will throw a code when it is only 4 to 6 percent plugged. I have put a gallon of paint solvent in the tank and driven for about 150 to 200 miles. I have used lacquer thinner. One other time on another car I took the catalyic converter off and soaked it dish detergent and water for a couple days then rinse with water. For the oxygen sensor test with a high impedance meter like an old Simpson 260
multimeter off ebay(about $65). The readings for O2 sensors can be found on the internet. If you need a new one, I usually buy the Bosch Brand. You usually can cross reference a GM number to a Bosch number. They are 1/4 to 1/2 price and probably better. Manufactured in Japan and not from the country of almost right.
It seems like there is a logical sequence to the MIL scanner readings. In your case if the engine was misfiring unburned fuel went out thru the catalytic converter and fouled it. Might have even crudded up the O2 sensor.
I would stop what your doing now, do not get so excited, read enough until your feel you have a little knowledge about the system. Know just a little bit about how the ecm and pcm and other sensors do on the truck. By a $50 scanner that tells you the code and the problem.
I will like to bet that more than 75% of the parts the so called mechanics put in vehicles are unneeded.
I like working on tractors. The only cars and trucks I work on are my own and a few friends.
Also, make sure you oil has been changed not to many miles ago. If the vehickle burns oil I put in 20% lucas Oil treatment and 80% motor oil. I thouht it was snake oil until I used in two higher price tractor engines.
Also, if you get it where the MIl does not come on you can do the GM method on how to start and the driving procedure(takes about 15 minutes).
I am jumping around with different ideas. Also it helps if you have 100 miles on it with no MIl before the gm test. Also, scan IM for 6 oks. You should have you gas tank between 1/3 and 2/3 full(helps you EVAP system work better.
One of the biggest problems I see is most guys are scared to get grease and dirt on their hands. And, do not want to learn how to use a good multimeter(the book that comes with a Simpson is about ten little pages). If you fall into either of these catergories take it to a repair shop.
Most vehicles(quite a few now) I usually spend between 25 to 100 dollars on. Also, remember you are working on a truck and not the space shuttle.
One last thing nothing to do with your truck. I do a little commodity trading(40 years and a hazard I got being in farming). Our Russian friend Vladimir Putin(a lawyer by education) controls thru himself and his companies 40 percent of the worlds supply of palladium which is the active catalyst in almost all catalytic converters. So,I hope external_link does not sanction him to much or the price of palladium(converters) could easily double.
 
I'vw had many issues with the distrubutor on my 2007 GMC 4.3L, Delco dist. So I went to Auto Zone and bought a 5 year distrubutor. Well it went bad just like the OEM delco. Took it back and they replaced it free.

Someone on YT suggested I put a coat of grease on distrubutor to keep the crap and moisture out. So far it's worked. I'm lucky to get 20-30k out of my distributors. That's why I gave up on delco's. Had the same problem with my 95 GMC. Every time I had distrubutor failure, it was extremely humid, raining, or condensation due to a rapid temp change.

As for rust, I took my 2007 GMC to Z-tech the day I bought it. Z-tech for under coat, sprayed bed liner and a wax job. Best money spent. No signs of rust. They put a lot of salt on roads in winter too.

I somewhat wished I had gotten the V8 engine. It has a distributor-less ignition and variable valve timing, I think that's what it's called. Where the v8 can become a 6 cylinder if you don't need the power.

George
 

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