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Ask someone: Scion XB engine wiring harness

I have a question if anyone has some advice. I have a 2008 Scion XB, 154k miles. The check engine light came on spitting out the code P0172. Which it looks like is typically the MAF sensor. So I brought it in to a mechanic, they said yes the MAF needs replaced. But they said also possibly the whole engine wiring harness might need replaced. They will let me know after replacing the MAF sensor.

I don’t know much about wiring harness but it looks like they cost north of $1,000 to fix. Here is my question…it seems that they don’t normally need fully replaced unless there is some serious damage (fire or something). I haven’t actually notice any symptoms while driving, it is normally smooth and no weird revving or anything.

Should I just not fix anything unless some symptom occurs? Should I find a shop that could fix whatever wire is actually broken? Or do I need to replace the whole dang thing? Any advice is appreciated.

I’d 1-have them show me exactly why the harness needed replacement, and 2-take it to another shop for a 2nd opinion, but only if I got another CEL/code.

You’re right, that’s a VERY unusual thing to replace.


Seconded. Do exactly what @texases said - something is very suspicious here.

Good deal. Thanks @texases @shadowfax. That is what I was kinda thinking. Thanks for the confirmation.

Unless it’s burned, chewed up by rodents, or disintegrating, I’ve never replaced a wiring harness.

To close the loop. They didn’t end up recommending replacing the wiring harness. He said that with a few specific codes on my XB for my model year, that sometimes the problem isn’t the code that displays it is the wiring harness. So he told me if it returns they might have to replace the wiring harness.

I don’t really see why you would need to replace the whole thing still, and probably wouldn’t take it back to them if the CEL comes back. It seems like you would at least be able to just fix the specific wire or connection, not the whole system. Regardless, car is back. No CEL so far, and runs normally smooth.