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Discussion Starter #1
Codes Popping for MAF (P0102), Both O2 Sensors (P0135 & 0141), and Evap System (0443)

Chance they failed separately, or could this be a systemic issue?

I’ve had this CEL on for a while now, and bought a simple OBD scanner a while back to try to figure it out. Saw that the codes commonly popping were emissions-related, and decided it wasn’t worth the hassle since performance wasn’t really affected. I would scan the codes and clear them every now and then and keep tabs on what they were, but never really needed to do something until transferring it to a state that does emissions testing.

First time I had it tested (using a self-service kiosk, the only way I’ve done it), I had recently cleared the codes, so the only one that popped was P0102 (MAF). I replaced the sensor, then had to get it retested. Since I didn’t bother to clear anything beforehand, the 4 codes I’ve seen most recently popped, even the one for the sensor I had just replaced.

So what are the odds that all of these systems have failed and need replacing? Because of how long I’ve let this CEL linger, I’m not entirely sure in what order and in what spacing they each might have failed, so it’s not clear if there was an order of operations, or if they all failed close enough together to be considered practically simultaneous, or suspiciously like a system issue that is affecting multiple things (or at least, causing multiple codes to pop). But since I replaced the MAF and that code is still popping, weeks later, could it be a dreaded wiring issue? I’ll give them a good look over to check for visible damage, but when it comes to car electrical systems, the extent of my knowledge is how to jump a battery and properly install a powered audio system.

I would love to just replace the evap thingy (for lack of a better term) and the O2 sensors and be done with it, but if there are some wires and connections I should test first so I don’t waste time and money, I’m for it. I have a digital mulitimeter, and actually just replaced the batteries not too long ago I believe.

This is an ’05 base model, with one of those k&n washable oiled air filters and a flowmaster muffler (all modification by previous owner, my stepbrother).
 

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Since these are all somewhat related, the first thing I would check would be the grounds for these components to make sure they aren't corroded/disconnected.
 

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OR the Exhaust fuse. This fuse supplies all these sensors. You may have a frayed wire or something...

 

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Discussion Starter #4
Seabass, how do I identify the ground wires for each of these components? Is there something like a common ground wire for them? I ask because I don't remember a separate wire going from the MAF sensor to a ground when I changed it, do I just need to follow the wiring harness back until I see something like a ground wire split off?

Coby, I'll check that fuse first, thanks for the highlighted map to it!
 

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Seabass, how do I identify the ground wires for each of these components? Is there something like a common ground wire for them? I ask because I don't remember a separate wire going from the MAF sensor to a ground when I changed it, do I just need to follow the wiring harness back until I see something like a ground wire split off?

Coby, I'll check that fuse first, thanks for the highlighted map to it!
Here's a post with common grounds that corrode
Grounds to check
 

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Discussion Starter #6 (Edited)
Okay, update time:

Checked the emissions fuse and it was blown, so I replaced it. Cleared codes, did a few test drives, everything looking great! But then I get a code pop again. This time, it's only P0135. And now that I think real hard about it, I do seem to remember that before I had the 4+ codes, back when I first tried to diagnose the CEL, P0135 might have been the one and only. Or maybe that's just wishful thinking? Either way, looks like I'll be swapping out the upstream O2 sensor.

I know it's probably a "best practice" to replace both O2 sensors at once, but what are the odds that it causes a problem?
 

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Just make sure you replace it with an ACDelco, and no need to replace both at once.
 

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Discussion Starter #8
Ah, so it's a no-go on the Denso?

I see 2 different varieties from ACDelco on Rockauto, the "GM OE" and the "Professional" ones. Is there any real difference there, and does it matter? Oddly, the "GM OE" is more expensive for the upstream, and cheaper for the downstream. I'll likely go with the $10 less "Professional" one, but since you specifically mentioned brands in relation to the replacement, if you have any further recommendations I'm all ears.
 

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Well, history showed that anything elso than ACDelco either don't work or don't last. Also make sure it's plug'N'play in other words don't get one with open ends.
 
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