Codes p0135, p0301 and p0404

1997 CADILLAC DEVILLE CONCOURS

84,000 MILES • V8

MASTEROFDISASTER

MEMBER
4 POSTS

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

SCGRANTURISMO

✓ASE Certified Mechanic
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

MEMBER
4 POSTS

Thanks Alex.

Jul 31, 2019 at 9:49 AM

STRAILER

✓ASE Certified Mechanic
54,832 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