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P0420 Code in 1999 Chevrolet Suburban: Cold/Hot Start Issues and No-Start Problems

Model: 99 Suburban Fault Code: P0420 Posted: 2006-05-30 17:38

My 1999 Chevrolet Suburban intermittently fails to start. It turns over but does not ignite, especially when the weather is cold or hot. The vehicle usually starts fine after sitting for 15–20 minutes. This issue occurs sporadically and seems to happen more frequently after the truck has been parked for several hours. Recently, AutoZone diagnosed a P0420 code, which they identified as a catalytic converter problem. However, I'm concerned whether this could be the root cause of my starting issues. The fuel pump hums normally when the ignition is turned on. I attempted to jar the tank during a previous incident, but no improvement was observed. When the truck fails to start, it behaves as if it's out of gas. I want to know whether the P0420 code directly causes these starting problems or if there’s another underlying issue. I have a 350 cubic inch Vortec engine and an aftermarket remote start system installed in 2000. The last time this occurred, the security light came on after the vehicle restarted—this was the first time that happened. I’ve been unable to check fuel pressure or spark during these events due to being away from home when they occur. I’m seeking advice on whether the catalytic converter is truly responsible for the no-start condition or if a more fundamental issue, such as low fuel pressure or electrical interference, might be at play.

Related fault codes
P0420
Comments (3)
Anonymous 2006-05-30 19:56

Could you provide your engine size, current mileage, and any modifications? Is fuel pressure adequate when the vehicle fails to start? Are there spark issues during these events? Do you have an aftermarket remote start or security system installed? I've encountered similar starting problems in older vehicles—sometimes related to these systems.

Anonymous 2006-05-31 04:54

I do confirm that spark is present when the vehicle fails to start. However, since I'm often away from home during these incidents, I haven't been able to measure fuel pressure at the time of failure. My engine is a 350 Vortec, and I have an aftermarket remote start installed in 2000. I’ll now test fuel pressure under normal conditions and investigate further. Interestingly, the last time this happened, the security light activated after the vehicle restarted—this was the first occurrence of that symptom. Thanks for your input; I'll update with more details as soon as possible.

Anonymous 2006-05-31 11:17

I suspect your fuel pressure is below 60 psi, which would explain why the engine won’t start. A P0420 code may indicate a clogged catalytic converter, but it’s unlikely to cause complete no-start issues—especially if the vehicle starts normally after sitting for a while. The converter might only be partially blocked and not severe enough to prevent starting. I recommend using a fuel pressure gauge during these events to verify this. If the filter hasn’t been replaced recently, consider doing so. Also, inspect the fuel pump harness for corrosion—it’s common in older trucks. Fuel pumps themselves are also prone to failure on these models. Focus on resolving the no-start issue first; it may resolve or at least reduce the P0420 code. Stay updated and keep us posted—good luck!