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2002 Oldsmobile Alero Won't Start with P0420, P044-2, and P0305 Codes - Fuel or Coolant Leak Suspected?

Model: 2002 Oldsmobile Alero Fault Code: P0305 Posted: 2015-11-16 16:01

My 2002 Oldsmobile Alero will crank over but won't start. The vehicle shows three diagnostic trouble codes: P0420 (Catalyst Efficiency Below Threshold), P0442 (Evaporative Emission System Leak Detected), and P0305 (Misfire Detected Cylinder 5). Oil appears slightly orange, with a noticeable antifreeze tint, which raises concern about coolant contamination. I've already inspected spark plugs and ignition wires—both show signs of wear and need replacement. The catalytic converter appears intact externally. While some users suggest a fuel pump issue, I can hear the fuel pump operating normally before starting. The gas cap is securely fastened. Given the presence of antifreeze in the oil and misfire code, I suspect either a head gasket failure or a vacuum leak—especially since this model uses GM's Dex-Cool coolant, which over time may degrade seals and lead to internal leaks. Should I proceed with further diagnostics such as fuel pressure testing, spark plug replacement, or a compression test? Any insights on how to prioritize these steps would be greatly appreciated.

Related fault codes
P0305P0420P0442
Comments (3)
Anonymous 2015-11-16 16:04

I inspected the ignition wires and fuel lines—everything appears in good condition. No major repairs have been done to the vehicle. A small residue was found near a vacuum hose on the air intake, which could indicate a leak or contamination source.

Anonymous 2015-11-17 07:20

Stick to fundamentals: verify fuel pressure and spark integrity. These are common root causes for starting issues in older GM vehicles like the Alero, especially when combined with misfire codes.

Anonymous 2015-11-29 22:12

This sounds very much like a head gasket failure. The 2002 Oldsmobile Alero uses GM's Dex-Cool coolant, which is long-life but can degrade over time and cause internal leaks. If the cylinder heads are warped due to coolant intrusion, it could prevent proper combustion and result in starting problems.