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Code 12 and failed smog

1770 Views 2 Replies 3 Participants Last post by  l4zy415
Hello Legend fans
I have my 90 LS aproximately 190K. Purrrs. Typical cold morning knocking but once it warms I can have a nice quiet dinner on the hood. Any way. Im getting a code 12 on the ECU. But my smog failed and the NO numbers wer well within the limits on both 15 and 25 mph. The only section I failed was on the 15mph HC (Max 78 Meas. 176) CO (Max 0.51 Meas. 0.75). I showed the results to the smog mechanic in town and he said that he would probably change the o2 sensors. Does this sound plausible considering the code 12 on the ECU?

I would appreciate any help or link to a previous thread. I have searched these threads but nothing concrete.


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Code 12 is the EGR system. You will need to clean the EGR system. It is probably clogged enough to throw the code. a new o2 sensor may help but I am leaning toward your EGR...

Ya, you'll need to clear the EGR system, or your EGR has failed. It is located under the distributor. And the metal tubing you'll see coming from the intake manifold is part of the EGR. There should be 2 metal tubes, one coming from the front header (long metal pipe), and the one from the intake manifold (short).
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