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.

Exhaust System Inspection $79.99 - $89.99 Get a Quote

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.

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

What others are asking

Ignition clicks on start, but will not turn over

Hey there, as far as the vehicle not starting while being jumped, there is a good chance the starter assembly may be experiencing a failure. Have the starting system tested by an experienced mechanic. The air not coming from the...

Car smells like something is burning or wet

Hello there. Based on the description you've provided, this seems to be a possible coolant leak onto a hot component of the engine such as on the exhaust pipe. Any part of the cooling system could be leaking. A good...

2006 GMC 2500 HD P0101 Mass ari flow sensor (MAF) performance

The powertrain control module (PCM) sends the mass air flow (MAF) sensor a 12-volt reference signal. Incoming air flows over a wire inside the MAF, which allows it to measure intake air temperature, and therefore air density. The MAF then...

What is shift lock release?

Most automatic transmissions come equipped with a solenoid designed to prevent the transmission from being moved out of park of the brake isn’t pressed. However, if the brake light switch malfunctions, the battery fails or the solenoid fails, you may...

Car running and idling rough

Hello. It is possible that your vehicle would need a complete tune up and/or a Check Engine Light inspection. I would have a certified mechanic scan your vehicle's computer for codes to diagnose your Check Engine Light. These codes may...

Rubbing noise from driver's front wheel while turning right

Look at the inner fender or track arm for signs of the tire rubbing on the parts. Your tires may be a little too wide for your vehicle. The fix may be to swap for a narrower tire. Also be...

P0171

The code P0171 is due to the left bank of the engine running lean and has reached the rich limit for the ECM. Try to have the injectors cleaned and run only high quality fuel that has cleaning additives. This...

2003 Nissan 350z code P0128 and had little smoke out my exhaust the night before the CEL came on. Any help?

Hi Jesus. Thanks for sending in your question. The P0128 code means that the engine coolant is not getting warm enough, fast enough. In other words, there is a problem with the engine operating temperature not being reached within a...

How to change a fuel filter in a 2005 Nissan Quest?

Hi there. The fuel filter is part of the fuel pump, so if you are wanting to change the fuel filter, the fuel pump must be changed as well. The fuel pump is located in the fuel tank and the...

Related articles

P0007 OBD-II Trouble Code: Fuel Shutoff Valve "A" Control Circuit High
P0007 P0007 code definition The P0007 code is associated with an electrical circuit which connects from your engine computer to your fuel system and is most commonly found on diesel engines. It also may be related to other codes, such...
P0235 OBD-II Trouble Code: Turbocharger Boost Sensor A Circuit Malfunction
P0235 P0235 code definition Turbocharger Boost Sensor A Circuit Malfunction What the P0235 code means P0235 is an OBD-II generic code that is triggered when the Engine Control Module (ECM) detects intake boost pressure sensor A input malfunction when compared...
P0595 OBD-II Trouble Code: Cruise Control Servo Control Circuit Low
P0595 means an issue with the cruise control servo control circuit which causes the cruise control on the vehicle to work poorly or not at all.