Codes p0135, p0301 and p0404

1997 CADILLAC DEVILLE CONCOURS

84,000 MILES • V8

MASTEROFDISASTER

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Failed emission test with codes p0135, p0301 and p0404. What parts do I need to replace and where are they located? I think EGR is one of those. Thanks, rg

Jul 29, 2019 at 2:03 PM

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SCGRANTURISMO

AUTOMOTIVE REPAIR CONTRIBUTOR
4,897 POSTS

Hello,

In the diagrams down below I have included the factory diagnostic troubleshooting guides for Direct Trouble Codes(DTC)(s) P0135, P0301, and P0404 for your vehicle. Please go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

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Jul 31, 2019 at 8:14 AM

MASTEROFDISASTER

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Thanks Alex.

Jul 31, 2019 at 9:49 AM

STRAILER

AUTOMOTIVE REPAIR CONTRIBUTOR
54,176 POSTS

I would start with the 02 sensor replacement

O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

This guide will walk you through the steps.

https://www.2carpros.com/articles/how-to-replace-an-oxygen-sensor

First sensor on bank 1 - Please let us know what happens.

Aug 2, 2019 at 3:57 PM