2004 Blazer 4.3l

Got a P0101 code, air flow meter is out of expected range. But I also have a P0155 code telling me that an O2 sensor is malfunctioning. I have a replacement O2 sensor and will be putting it on this week (actually got all 3 off a donor vehicle in a junk yard with only 40k miles on it!)


Just wondering, can a misreading O2 sensor make the code for the AFM to throw too, or would it have no connection and I should start looking for a replacement AFM too?


I've cleared them for now just to make sure it's not a fluke, but I expect them to come back... Truck is getting HORRIBLE gas mileage, like 200 miles to a full tank...

Also have a P0452 code telling me the pressure sensor on the tank is gone, but I'll be putting a new fuel pump assembly in it soon anyhow because the level sensor is shot...



Also, just a shout out, if anyone has ever wondered about the Torque app for Android, it is simply awesome. Been using it for a few years now between several vehicles. WELL worth the $5 for the app and $25 for a cheap bluetooth OBDII dongle off eBay







here's all the sensors it is capable of picking up for live data

 

The data displayed is entry level, and most scan tools should display it, basically the software is one level up from a code reader. It's good basic information to have, if you know how to interpret it.

The first DTC, P0101, needs to be diagnosed & repaired first. Any subsequent DTC's can be caused by the first one. The first thing to check is fuel pressure and leakdown. They are not monitored by the PCM so they can not directly set a DTC if/when there's a failure. If fuel pressure is low, and or leakdown is excessive, fuel mileage goes right out the window, and it's quite common to set MAF and upstream O2 sensor DTC's when that happens. The P0452 indicates a problem with the fuel tank pressure sensor, or the circuits for it, not necessarily a bad sensor, or it may have set because of the other two DTC's. Check fuel pressure and leakdown first and post the results.

 

10/4, thanks I do not have a fuel pressure testing gauge, but I'm sure someone at work does


yeah as far as trouble codes and scanning them, I know this app isn't going to do anything beyond basic, and I would never expect it to for $30 all in :P I've also got the ABS light on and a guy at work has about a $1200 scanner that he's going to throw on it so he can tell me exactly WHY it's on, be it the module or a specific wheel speed sensor

 

$30 is a darn good price, that's usually about what code readers cost! Front wheel speed sensors are real common failures on these... but you gotta replace the whole hub assembly The scan tool should pull up a DTC and point you in the right direction.

 

what's the procedure for fuel pressure testing? I know I've seen it before but I cannot seem to find it again

 

https://blazerforum.com/forum/tech-a...agnosis-23038/

 

awesome, thanks!

got an AFM off the same vehicle I got the O2 sensors off of today as well. since I have them in hand it it might only take me 15 minutes to change both, I might try swapping those to start with and see what happens


I should also note that aside from the low MPG, there seems to be no driveability or running issues. it fires right up and doesn't miss a beat, runs smooth, no smoke from the tailpipe, no foul smells, plenty of power, just drinking gas...

 

Well before I even left the parking lot of work yesterday I changed the AFM, simply because it's an easy replacement. Cleared the code and then headed into town before heading home. SES light came back on, scanned it and I'm still getting the P0452 for the fuel tank pressure but I expected that. The AFM and O2 sensor codes have not came back on yet, which is good since last time I cleared them those threw almost immediately. Going to run it for a few days and see what happens.

 

well the O2 sensor code threw again... AFM code hasn't came back though. fuel mileage hasn't gotten any better since swapping the AFM either. I went ahead and swapped out the O2 sensor this afternoon and cleared the code again, so we'll see what happens now. hopefully it does something for fuel mileage, this 200 miles to a tank crap SUCKS

nice thing about working in a junk yard, I pulled the AFM and all 3 O2 sensors off another 04 Blazer that came in that only had 40k miles on it, and only paid $15 for it all that thing was mint! well, accept for the rear end collision... I also got the front seats, front door panels, and speedometer/radio bezel

 

I used my buddy's snap-on scanner and looked at the ABS system. No reading at all from the front right sensor. Nifty little scanner though, I was able to run a function test on the rest of the ABS system, so I know everything else is in working order

Been doing some digging around today at work (junkyard) and unfortunately these monkeys cut the brake fluid and sensor wire 90% of the time they pull anything off the front end... so every 4wd I went to was a complete bust for a sensor... but then I got to digging around some more and pulled a couple sensors off a full size Chevy with good wires, as well as some good sensors off an 04 2wd Blazer. At a glance, the sensors look IDENTICAL at the business ends (the sensor that bolts to the hub and the other end that plugs into the harness on the frame), the only difference looks like the length of the wire and the spots in the wire where it's held out of the way to the upper control arm. The full size truck sensors are LONG, LOTS of wire to play with, so I'm going to attempt to use them. Maybe I can route the wire in a way to keep it from rubbing on anything and rubbing a hole in it... of the ones I looked at, that seems to be pretty common on these... I also dug up a couple shims that go between the sensor and hub too, in case there seems to be some interference (seems like as I was looking around, some had the shims and some didn't...)

So yeah instead of just replacing the entire bearing hub assembly, I'm going to start by just trying to replace that sensor. Not like it's going to hurt anything, the ABS already doesn't work right