Well lets see... the SES light started coming on this past week, i pulled the codes P0131, P0137, P0151 all O2 sensor low voltage codes, I cleared them out drove the car and all was fine for a few days then SES light again but only after major hesitation and misfirinf at take off or during hard accelleration/ passing. ran codes again and got: P0131, P0137, P0151, P0300 (multiple cylinder misfire) went to Pep Boys and service manager advised me to change the 2 pre cat O2 sensors (in the y pipe) and also stated that he thought but was not sure but he got a tech memo stating that condensation drip from the A/C pipe onto the Bank 2 sensor 1 has caused sensors to go bad, he also stated that GM has failed to recognise this issue as a recall. He was not for sure that it was the blazer though or another SUV. My problem remains, when first started the car has all the power and get up and go in the world, will actually burn the tires from a dead stop, when it warms up there is all kinds of hesitation at hard acceleration, if i baby it it will go but if i step on it it bogs, hesitated, then begins misfiring till i back off the gas pedal. these are the only codes it has thrown and it has thrown the SES light 2 times now. Do you think it is the O2 sensors or what. It is a 2002 Blazer LS 4WD, 4DR with 78.887 miles on it.

 

anyone?????? cat got your tounge??? I know there are some very knowledgable people on here that have opinions or expertice in this matter so why not help someone out??? and as for searching the knowledge base, i already have done that and gotten no information relevant to my specific problem.

 

How impatient can one person be? Makes me want to jump up and answer your question for you! But anyway...

I have never heard of the A/C dripping condensation onto the B2S1 sensor. From the position of this sensor, there isn't an A/C pipe within 2' of it, and the HVAC drain is quite a ways forward as well. Not to mention that the O2 sensor is a sealed unit and is constructed to work in a monsoon.

Now the reason why it runs fine until it warms up is because the O2 sensors really are not being used until the ECT is over 160*F.

Lets just run down through the codes you have listed:
P0131 - O2 Sensor Circuit Low Voltage (B1S1)
P0137 - O2 Sensor Circuit Low Voltage (B1S2)
P0151 - O2 Sensor Circuit Low Voltage (B2S1)
P0300 - Random/Multiple Misfire Detected

The missfire code is mostlikely caused by the O2 sensors being out of wack. Now do these codes mean that your O2 sensors are gone... Well, probably not. It is HIGHLY unlikely that all 3 sensors would have the same fault.

If you have a scan tool that can view the sensor data, the first step would be to monitor the HO2S voltage and ensure that it is a 99mV. Next would be to check the wires for shorts or worn insulation, ny water intrusion into the HO2S connector, An exhaust leak between the HO2S and the engine. An intermittent lean engine condition such as: a vacuum leak, an incorrect or defective PCV valve of system, an incorrect fuel pressure, any lean fuel injectors, an inaccurate MAF sensor, a lean engine condition during power enrichment operation (warm up).

Now if you verify that the HO2S voltage is 99mV somehow, then the list goes on...

First thing I would do would be to inspect the wiring harness off of each one of the sensors. Pull each sensor's connector apart and spray liberal amounts of electrical contact cleaner into/onto both connectors and leave unplugged until dry. DO NOT use any dielectric grease in the connectors. The HO2S uses it's wires to draw fresh air into the sensor as a reference to the exhaust O2 content.

Also, remove the MAF sensor, disassemble it, and CAREFULLY clean the sensing elements. They should look alittle gray to white in color. If they look brown or even worse, black, then that right there could be your problem.

Check your plugs for signs of a existing lean condition to help narrow down which end of the system we should look into further.

Atleast you've got some direction now. You could have replaced all 3 sensors and not accomplished a thing except lightening your wallet.

You haven't gone parking in flooded roads lately have you?

 

Thanks for the info, impatient? not really, first post was days ago with no response, I think i waited a reasonable time to ask for more help. anyways, i see you are from seneca falls, i grew up in rochester, charlotte to be exact. The car has not seen any floods lately or to my knowledge, where is the maf sensor? i really do not have access to a scanner to monitor the sensors, i will however begin by doing the steps you mention such as checking connections, cleaning sensors etc. Can you possibly give me the location of the sensors. The only work recently done to the car was the installation of the sound system, head unit, amps, speakers and subs. this was professionally done by an install shop. new power wires were run into the engine compartment for the stereo but i do not think they came close to disturbing any sensors? i did today change the air filter, the old one was fairly dirty, i bought a K&N one to drop in.

 

Well, it is impatient given that you posted again within a few hours on the original post above. I must have missed your first post on this subject. I'm going to post a link back there and lock the previous thread so as not to have two ongoing discussions of the same topic.

Were you having these problems before the stereo install? What kind of voltage is reading out at the in-dash voltage gauge?

The MAF (mass air flow) sensor is located in the intake duct between the air filter and the throttle body. I posted some pictures with a small how-to awhile back. Seems that our search engine is not working properly. I'll have to look for that later. If you can wait, do not clean it until you see what I'm talking about. The MAF sensor is very sensitive when apart and seeing as how it's $250+ to replace it, you don't want to ruin it by accident.

If the problems started around the same time as the stereo install, check all locations where wires were drawn through the firewall for wire damage from a drill or from sharp metal.

 

Lets see, the problem did not exist prior to the installation of the stereo which was last friday evening, it surfaced on or about monday evening of this week, if it was present before it was unnoticable, there was however (back in december of last year) a time when i was driving back to rochester and going thru the pocono's i noticed some power loss, while in rochester the fuel pump went and was replaced by a very reputable shop (Zona Automotive) The system was scanned at that time (for NYS inspection). It ran fine up till now. It is pouring rain now or i would go out and begin checking connections and where wires were run. As far as the dash voltage gauge before and after the stereo install it is kinda generic but looks to be reading the same (about 14 volts) or slightly above occasionally slightly below if A/C is running etc. I have not crawled under car yet but do not hear any exhaust leakes. While revving up engine on first day of SES light it did make small popping noises on decelleration reminicient of an exhaust leak but that was the only time that ever happened. car is very quiet inside and out. I will make a physical inspection of exhaust as soon as i can.

 

This sounds very similar to a problem my parents had with their '97 STS. Their problem was a corroded ground for the heaters on the O2 sensors. So the codes were different, but they had a code for all 4 O2 sensors and multiple codes for each at that. Their car would run decent although it was running quite rich. I attempted to find the location of the grounds for the O2 sensors, but couldn't find an exact location of those exact grounds. If you see any grounds under the hood while poking around, just remove them, clean them up, and put them back together. That's just good preventative maintenance.

Sounds like you've got a bit of work to do. Give those things a try and see what happens. Good luck.

 

I just got back from the store and the car ran perfect, all kinds of power and no hesitation, no misfires or anything... weird!!! i drove it on both highway and city driving for about an hour or so. what could that mean, the only thing i did today was change the air filter to a K&N brand filter and nothing else. I am really stumped! for a minute with the a/c on on a city street, it slightly hesitated but only the one time, after that it was perfect, and that happened 5 minutes into my trip! actually the car temp gauge was not even warmed up all the way when that happened. Do you think it is a faulty wire or ground somewhere?

 

hey just thought of something else that is weird and been hapening. sometimes my gas gauge reads less than what it actually is, example, yesterday i put in $20.00 on the way home, it gave me just over a quarter of a tank, today i drove the car earlier in the day and when it started it read 1/4 tank but 2 minuted later the low fuel light came on and it read E! then when i came out of the store the light went off and it read just under 1/4 tank again?????? all this is making me wonder if the ECU? computer is malfunctioning. I read a few posts on another forum that the ECU on some year 4.3's were corrupted and need to be overwritten/reset.

 

Naw, my fuel gauge does that in my Bravada as well. It depends on how much of an incline I park on though.

I would atleast do the cheap stuff like cleaning the connections and grounds. And inspect the wiring harness under the hood down to the O2 sensors.

As far as where the sensors are located... B1S1 is located on the driver's side y-pipe. B2S1 is located right before the 'y' in the y-pipe on the passenger side. And B1S2 is located directly behind the catalytic converter.

This definitely sounds like an intermittent problem. But before diagnosing this as an ECU problem, you really need to check the above.