I've got a PO420 catalyst system efficiency below threshold bank 1.

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It came on after I changed my thermostat. What needs to be done now?

Dec 6, 2014

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What are the best Chevrolet repair shops?

RepairPal Certified shops can diagnose and repair your 2004 Chevrolet Trailblazer. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.

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What is your question?

Popular Answer

I've got a PO420 catalyst system efficiency below threshold bank 1.

What is your question?

It came on after I changed my thermostat. What needs to be done now?

Penny123 in Pearl MS

Dec 6, 2014

1 Reply

Popular Answer

pushrodon Dec 7, 2014

Professional scanner set to live data can monitor sensors to see IF converter is working!! That's what needs to be done! Possible failed rear O2 sensor or its circuit but must be tested...

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Popular Answer

What are the best Chevrolet repair shops?

RepairPal Certified shops can diagnose and repair your 2004 Chevrolet Trailblazer. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.