Q: P0420 code and engine is not starting.

asked by on December 25, 2016

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

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

Engine starts but dies after 3-5 seconds

Hi there. This can be caused by a fuel rail pressure sensor, but most of the time when this code comes up it is because the fuel pump has failed. A fuel pump will fail much more often then this...

Replaced the power steering pump and now car won't start.

Hello there, you have a few different faults going on with your 2009 Chevrolet Impala. The power steering repair should not effect the vehicle starting in any way. There are many common causes for the vehicle to not start such...

Filling an MDX Acura with diesel instead of regular 2002 Acura MDX

Hello - your best bet is to have the diesel fuel drained from the fuel tank by a professional mechanic, replace the fuel filter, then refill with premium fuel (for highest possible octane rating to compensate for effects of any...

Related articles

P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 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 pressure sensor B input circuit range or performance...
P0359 OBD-II Trouble Code: Ignition Coil I Primary/Secondary Circuit Malfunction
P0359 P0359 code definition The P0359 code indicates that a fault has been detected in one of the vehicle’s ignition coils, generally the number 9 coil. This code can also be associated with P0351, P0352, P0353, P0354, P0355, P0356, P0357,...
P0453 OBD-II Trouble Code: Evaporative Emission Control Pressure Sensor High Input
P0453 code means that a reading from the engine’s evaporative pressure sensor is higher than normal due to fuel tank vapor leaks into the system.