Q: P0420 code and engine is not starting.

asked by on

Got the SES light on a few days ago. Checked for the OBD code, got a P0420. Continued driving, felt a little lack of power 2 days ago on the highway at 120 km/h.

Yesterday morning, when I tried to start it, the engine cranks up, but does not fire up. Battery is good, replaced a few months ago. Engine cranks normally, but shuts down with a cluttering sound.

Is there some engine damage, or the ignition/plugs are misfiring, which might have caused the P0420 in the first place?

Will a detailed diagnostic help?

Thanks.

My car has 115000 miles.
My car has an automatic transmission.

Hi there. The p0420 code means that the catalytic converter is below threshold and is not functioning correctly. This code comes up when the catalytic converter can no longer burn off any fuel in the exhaust system. Take a raytech gun (thermal gun) and check the temperature of the pipe before the catalytic converter and check the pipe after the catalytic converter. If the temperature is the same, then the catalytic converter is not working and would need replaced. If the temperature is 100 degree difference, then the down stream Oxygen sensor has failed. Either way, then computer sees this and has put the engine into limp mode and is making the engine run poorly and stop running. Since you are hearing a strange noise as the engine is not starting but cranking, the catalytic converter could be plugged up causing a restriction on the exhaust system. I recommend seeking out a professional, such as one from Your Mechanic, to help you diagnose your exhaust system.

Was this answer helpful?
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
  1. Home
  2. Questions
  3. P0420 code and engine is not starting.

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: The car shakes during braking and at stop lights, error code P0420

Hi there. The P0420 code you are getting can cause your car to run like this. The code typically means that the catalytic converter is failing or one of the oxygen sensors may be failing. If it was the...

Q: I'm wondering why my car won't start in 50 degrees or lower temperatures

Hi there. If your engine is cranking over and it's difficult to start, the issue may be caused by a damaged distributor or ignition coil. Especially if it's cracked and condensation is seeping into the electrical system. Other possible...

Q: Even though I replaced battery, car won't start.

If the battery is brand new and fully charged and the car turns over but will not start the battery is not the problem. The electrical aspect of the starting system is doing its job. Engines require fuel compression and...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...