OT-diagnostic codes

I own a 01 Chevy S-10, 4.3 v-6. Started running poorly even had a fail to start one day, but started just fine next. Took it to my favorite auto parts store to check diagnostic codes. Showed Mass airflow, bank 1 O2 sensor, bank 2 O2 sensor, crankshat position sensor, egr, and multiple random misfires. How does one move strategically through the code diagnostics. I would like to not just " throw money and parts at it" but move logically thru the process. I'm probably over my head here but would like to try. thanks for you assistance....gobble

My bet would be to replace the crank position sensor. Both 02 sensors have effect on the engine and running, it's just a monitor for emissions, my truck ran fine with a bad 02 sensor for a year until I had to replace it for the truck check engine light to go off to pass emission inspection. As far as misfires my ford had a bad coil on top of the spark plug, not sure if yours is the same a coil for each cylinder.

Ment o2 sensor has no effect on engine running,

Check for vacume leaks..

Mass Air Flow sensor can be cleaned...special product available every where. Try this before replacement.

I would record and then-clear the codes.See if any come back after driving,and starting a few times.If you have access to a wiring diagram it is possible all these sensors share a common ground,and causes all the fault codes.But like Jay said,probably the crank position sensor.It is best however,to know what the expected result of each fault code is.This where access to diagnostic manuals is a big help.Mark

Like mentioned, record the codes and clear them and see what comes back. It would be better in the future to provide actual code numbers when they come back too. All these codes could be related in some way or another, or several of them may be triggered as a result of another code/failure.

MAF and o2 codes can be a vacuum leak (vac lines, intake gaskets, crankcase breather tube, air intake breather tube) or faulty MAF, might try cleaning MAF. These are just possibilities, actual code numbers might help.

Crankshaft position sensor ( CPS ) and misfire codes could be from faulty sensor, ignition parts ( plugs, wires, cap, rotor & coil) oil leaks on front of engine timing cover have been known to leak into the CPS connector causing problem. The EGR valve if stuck open could cause misfire problem too again this is depending on what codes you have.

That system will throw you all kinds of curve balls if the fuel pressure is borderline low BTDT got the T-shirt. Yours fits the bill with all the symptoms of a pump that is borderline.

KOEO (key on engine off)
KOER (key on engine running)

KOEO fuel pressure 65 PSI its regulated at 65 and could make 100 if not regulated.

KOER 55 to 60 nuttin less than 55 at idle. NOW the kicker and what you need to focus on,,, anytime you apply throttle the fuel pressure should go to 65 and stay there under any load no mater how small are how big. If it can not maintain 65PSI under a load the pump is not able to supply enoufh fuel to the engine under those conditions. Your MAF will be under reporting for the conditions, the O2's will be driven lean and it may show multiple misfires. A tip may be its a dog under full acceleration it may pop back thru the intake. Another tip is it is slow to start but starts as soon as you let off the key. And of course it may not start at all intermittently.

If its a pump make sure the tank is clean no rust spots anywhere including the most over looked place THE UNDERSIDE OF THE TOP OF THE TANK. That one may be plastic it needs to be clean also.

You're going to think I'm crazy, but I had three of those codes on my 2011 Traverse about 5 months ago. I took it to the dealer and he read the codes, then said they couldn't get it to duplicate. He suggested it could be the coil for #3 cylinder, but that would require removing the intake, would cost @ $350 . . . . and then went on to say "that may NOT fix it." I said, lets clear the code then run it till we do know what will fix it. I then put a can of Seafoam in a half tank of fuel. Ran that thru and the code did NOT return. I put a second can in the tank again when it was @ half tank. I have had NO codes since. Food for thought.

Bad info jay.
Upstream O2 sensors give input to the pcm for engine performance, downstream ( after the converter) are only catalyst monitors.
Hobo has it check fuel pressure. Plugs,wires,cap,and rotor are maintenance items and be sure to buy a good quality cap.
Also if the MAF code is a voltage code then the sensor is probably faulty.

Good call. my pump regulator on a Chevy HHR was bad. Threw codes all over the place due to lean burn. Key was intermittent hard start. There was a shrader type fitting to hook a fuel pressure gauge to. You may be able to borrow a pressure gauge at a chain auto parts store. Good luck.

I did not know the code heading could be useful, here goes-P0 101 MAF mass air flow, PO 171 bank 1 O2 sensor, PO 174 bank 2 O2 sensor, PO 300 multiple random misfires, PO 335 crankshaft position sensor, PO 404 exhaust gas recirc (egr). After reading all of your posts, I think I will attack first, the plugs distributor cap and rotor. I do not know when they were last changed. Consider it periodic maintenance. Then will clean the maf with the special cleaner in a can. Will change the crankshaft position sensor. Then will see what that does. Will get the codes erased? and then see what happens. Thanks to each who has taken time to help. I appreciate it. I'll report back with my results. gobble

You don't have an over oiled K&N air filter in it, do you? That can screw up the mass air flow sensor. If your 01 has a flat dist. cap, they were also a problem along with the rotor a coil wire. I had a fancy 97 GMC Jimmy that I was very happy to see go, hated that thing.

Lots of good info here. I found another good site for GM. Its called "Silverado Sierra.com" Check out trouble shooting there also.

I can't remember if mine was up stream or down stream, but my truck ran fine, iv never heard of a bad 02 sensor causing bad engine running, now the vent valve is bad on my truck, so check engine light has be on for the last year. Still no engine running problems.

The P0171 and P0174 are not O2 sensor codes, they are fuel trim lean codes. I would start there and/or with the MAF code. P0101 is highly uncommon with that engine, the MAF on those almost never fails. I think you MAF code is causing the lean codes, in turn causing your misfire code P0300. I would also want to see a scope pattern on the crank sensor. Start by checking fuses, the MAF and crank sensor require 12V feed. I have seen a mild short to ground near the trans dipstick bring the 12v feed low enough to affect the MAF signal, yet not pop the fuse. You could have low fuel pressure, like Hobo said too, worth checking. At this point, your cap, rotor, wires, and plugs is unlikely to change anything. You really need a scan tool that shows data for the sensors in question, otherwise you are flying blind and waving money.

This is a very interesting discussion. My 97 S10 blazer is showing some of the same codes. History is that I put a used engine in it four years ago and has ran fine up till a few weeks ago and the son ran it out of gas because of a miss-reading fuel gauge. Put a new assembly in and it ran fine the first tank and a half then faltered throwing the MAF code about low voltage and we barely got home. The fuel gauge also was working OK but when it faulted the gauge went down and then all the way past almost to the 3 o'clock position. I pulled the tank again and checked the pump , it had good flow at the beginning and slowed down after a quart of gas was pumped(about 7-8 gallons was in it). The Ohm value of the sensor read good. Put it all back together and drove it out of the garage and the gas pedal seemed to stick with it running at 1700 RPMs. The throttle plate was closed at this time. Shut it down and it restarted with a slower idle but not completely down to 600. The gauge was working for the first five minutes and the jumped all the way over again , after shutting it off a couple times it went to reading close to where it should read.

I have not had the time to check the fuel pressure yet which HOBO commented on.
Sprint where did you find the short , in the main loom or can you give me a more closer place to look, it almost sounded like something tripped when it ran weirdly.
I will get back to working on this after my kidney stone passes which stopped me for now from doing anything outside.
I really appreciate the help you guys can give and will let you know when, If, I get mine repaired, Kinda frustrated right now with it.

thank you, I appreciate your input gobble

thanks for sharing. Hope your plumbing issue is resolved quickly. gobble

I'd start with the EGR. It takes a very small piece of carbon holding the pintle open to screw up a lot of the other things it is coding for. Second would be a good fuel supply check. Be careful cleaning the MAF. Those little sensor wires aren't robust. On the same line, a very little dirt/lint on them with do all the same things an EGR will to screw it up.

(quoted from post at 09:07:53 01/03/17) I did not know the code heading could be useful, here goes-P0 101 MAF mass air flow, PO 171 bank 1 O2 sensor, PO 174 bank 2 O2 sensor, PO 300 multiple random misfires, PO 335 crankshaft position sensor, PO 404 exhaust gas recirc (egr). After reading all of your posts, I think I will attack first, the plugs distributor cap and rotor. I do not know when they were last changed. Consider it periodic maintenance. Then will clean the maf with the special cleaner in a can. Will change the crankshaft position sensor. Then will see what that does. Will get the codes erased? and then see what happens. Thanks to each who has taken time to help. I appreciate it. I'll report back with my results. gobble

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When you replace the crank sensor if it has hit the trigger wheel they make spacers for it . If the connector is oil soaked replace it also.

This is why a good mechanic gets the big bucks he does not pull out the parts cannon and shoot parts at it. Can someone tell me why DIY'ers shy away from preforming a few simple test the same test your overpaid wrench should preform. It could be multiple issues they are always fun :evil:

All you can do is logically progress through replacing parts. You do not have the equipment or expertise to test the electronic sensors thoroughly, and given the age of the truck, they are likely to need replacing anyway.

I've personally never understood why people think so unkindly of "parts replacers." That's how you've always fixed things! The only difference between then and now is that instead of standing there scratching your head as to which part to replace next, a computer tells you which part to replace!

thank you

Nothaving access to a detailed flow chart. I was hoping that by asking I would not just be throwing parts at it. Mostly seeking past experience of others with a machine such as this. I was assuming the domino principle was in play. That if one component failed, others downstream so to speak would be triggered. I do not begrudge the mechanic or his charges for doing work. A craftsman is worthy of his hire. But a vehicle this age, you can get upside down at the repair shop pretty quickly. gobble

The most efficient way to tackle this is to start out by clearing the codes. Then, you address the first code that reoccurs.
As another poster stated, P0171 and P0174 are mixture codes. That are telling you that the mixture is too lean. When I see both of these codes together, I suspect that there is nothing wrong with the O2 sensors. There are MANY things that can cause lean codes. As already stated, fuel pressure is a possibility. A mass air flow sensor out of calibration is also a possible suspect. Next in line is possible air leakage in the intake stream. Last but not least is it might need a valve job. I know that sounds far-fetched, BUT... on many of the V-6 engines of that era, they have soft valve seats. After a lot of miles, the valves beat their way into the head. This is a difficult problem to diagnose. I went through this on my own car. After exhausting all other possibilities, I pulled the heads. Found that the exhaust valves were beat about an eighth of an inch into the head on one bank and the head was cracked in between the intake and exhaust valves as well. A valve job cured the problem.

Keep in mind that there are some things like the crankshaft position sensor that will stop the engine. It simply will not run with a bad crank sensor. EGR codes are not critical, but will light up the check engine light. In any case, you need to start out by clearing all of the codes and see what comes back.