CEL lights after precat removal

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CEL lights after precat removal

Post by australianpianoman »

Just got my mechanic to take out the precats on my new-to-me 2001 mk3. I’m now getting all the o2 sensor heater circuit codes- 135, 141 and 155. Is this the post-cat sensor having a fit because it’s not getting the readings it’s expecting or have somehow all sensors failed at the same time? I’ve done lots of searching on the issue but I haven’t seen anyone come across all of them firing at once. Loving the car otherwise, only 60k miles, it’s a hoot! Any help appreciated



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Re: CEL lights after precat removal

Post by MRHAPPY62 »

Have you tried a reset , disconnect the battery for a while , just a thought .
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Re: CEL lights after precat removal

Post by australianpianoman »

I did clear the codes after the first time and they fired again today, I’ll try disconnecting the battery tonight and get back
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Re: CEL lights after precat removal

Post by jimi »

Sounds more like your mechanic has disturbed something, have you checked the plugs/connections to each sensor ?
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Re: CEL lights after precat removal

Post by australianpianoman »

I reseated the plugs to the sensors and disconnected the battery for ten minutes, took it for a spirited 1.5 hour drive and the eml light has stayed off. Hopefully that’s sorted it for the sweet price of £0 but maybe it’ll come back on after a few engine cycles, will report back either way! Thanks for the help
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Re: CEL lights after precat removal

Post by jimi »

:th: Result, hopefully it will stay that way :cool1:
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Re: CEL lights after precat removal

Post by australianpianoman »

On goes the light again, and again all three codes popping up. I wonder should I replace one sensor to see if it shuts off that code before buying the other ones, or is it worth trying to solder in a resistor to trick the ecu? Also, will I be running rich and damaging the main cat if I drive it in the meantime?
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Re: CEL lights after precat removal

Post by jimi »

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Re: CEL lights after precat removal

Post by demetriz »

Ever since I deleted my pre-cat, the check engine light has been on. My mechanic chucked in a used O2 sensor that was known to work, but after a while the light came back on. He says its because of the pre-cat delete. Any ideas?

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