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Discussion Starter · #1 ·
Hi All,

Looking for some advice before I start replacing parts. I have a '13 FoST. The car has been running great, no codes. I installed a catless downpipe and 3" exhaust a week ago. Started and drove around the block ok. After restarting, the CEL came on immediately. Checked the codes with my APV2 and had a P0135.

I rechecked the installation, connector and wiring and everything seemed ok with no clear signs of damage. I reset the PCM and the KAM, P0135 consistently returns after the 2nd start. Since then, I've triple checked that the connector and wiring has no damage and is away from any heat source. I've checked every fuse, and tried a different tune. Also, while monitoring the A/F ratio with the AP, it's stuck at 14.7 while driving.

I'm assuming this means I'll need to replace the upstream o2, I'm just pretty confused about why it failed. I was pretty careful to prevent any impacts during the R&R.

Any tips would be much appreciated!
 

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Heater element is probably burned out of oxygen sensor. You can ohm test the heater by checking resistance if you have a multimeter.
 

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Discussion Starter · #3 ·
That's what I'm thinking too. The replacement sensor are inexpensive enough that I'm just going to replace it. If it's not the sensor, it's gotta be the pcm I'd imagine. The wiring in the area all looks ok.
 

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Discussion Starter · #4 ·
Just an update, I replaced the front o2 sensor and the CEL has stayed off so far. It would consistently come on immediately after the 2nd start, but has stayed off for a few starts. Need a few days of driving to confirm it’s fixed though.

It was pretty simple to replace. Drove it on ramps and let it cool for half an hour after my hour drive home from work. From removal of the lower engine cover to reinstalling the cover was roughly half an hour. Ramps REALLY help cut down on labor time though, and they seem safer than jack stands.
 
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