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2000 Isuzu Rodeo Check Engine Light Returns with Code PO42-0: Causes and Solutions

Model: 2000 Isuzu Rodeo Fault Code: P0420 Posted: 2006-11-02 15:58

My 2000 Isuzu Rodeo experienced a blown engine, which was replaced with a used engine having 40,000 miles. The installation was performed by an unqualified mechanic. Upon pickup, the check engine light remained on and blinked during acceleration. The vehicle also exhibited rough idling and poor driving performance. A scan tool revealed code PO300. After extensive troubleshooting, I took it to the dealership, where a technician identified that the oxygen (O2) sensors were incorrectly connected to the wrong sensor banks, resulting in misfires. Once corrected and the code reset, emissions passed. However, later that night, the check engine light reappeared, and my scan tool showed code PO420. I cleared the code, and it has not returned for over 24 hours. Despite proper O2 sensor installation, the issue persists. What could be causing the return of the PO420 code after the fix? Is there a possibility of an exhaust leak or other underlying issues related to the engine replacement?

Related fault codes
P0420
Comments (3)
Anonymous 2006-11-02 16:44

An exhaust leak in the manifold area, especially from the engine installation, could be causing the PO420 code. This is a common issue after engine swaps.

Anonymous 2006-11-02 17:13

As someone with limited experience in mechanical repairs, what steps should I take to diagnose this issue myself?

Anonymous 2006-11-02 18:01

Have the vehicle inspected by either the mechanic who installed the engine or the dealer that reconnected the O2 sensors. An exhaust leak upstream of an oxygen sensor can trigger a PO420 code. Additionally, a faulty catalytic converter could also be contributing to this issue.