P0420 Diagnostic and Repair for 2001 Chevrolet S10 2WD with Starting Issues and Brake Light Problems
I own a 2001 Chevrolet S10 2WD with a 2.2L engine. The check engine light has been on for approximately one year, and the fault code displayed is P0420. About 8 out of 10 times when I attempt to start the truck, it cranks for 8–10 seconds before starting, and the vehicle exhibits noticeably reduced power compared to its original performance. I have already replaced several components including the fuel pump, control module, spark plugs, spark plug wires, catalytic converter, and both oxygen sensors. Despite these changes, the issue persists. Could there be another underlying cause for the P0420 code or the starting difficulty? What additional diagnostics should I perform? Additionally, unrelated to the check engine light, my brake lights frequently stay on—sometimes even activating when the truck is idle. I have replaced both the brake light switch and the combination switch without resolving this issue. Could there be a wiring short or an aftermarket device (such as a security system or remote starter) interfering with the brake light circuit?
The P0420 code typically indicates a failing catalytic converter, but it's important to verify whether the starting issue is related. You should first confirm proper fuel pressure and ensure that ignition components and engine mechanical systems are functioning correctly. As for the brake lights, check if any aftermarket devices—such as a security system or remote starter—are wired into that circuit, as they may be causing the lights to remain on or activate unexpectedly.