Stop CEL With Test Pipes
From Nissan 350Z & 370Z Wiki
If you are getting a CEL (check engine light) after installing high flow cats or test pipes, then you need this easy fix. No expensive 02 simulator is needed. They are more $ and more work than is needed. The HELP! method is tried and proven to get rid the test pipe related CEL.
Get two packs of HELP! Spark plug nonfoulers - part number 42002 or 42009 (either will work) - these are readily available at Autozone, Checker, Pep Boys, etc.
Drill ONLY 2 of the nonfoulers out with a 1/2" drill bit. Fit 1 NON-drilled fouler into each test pipe. Fit 1 drilled nonfouler into the previously installed undrilled fouler on each bank. Finally insert your o2 sensor into the drilled nonfouler and reconnect the wires.
THAT IS IT! Reset your ECU and the CEL will not come back!

