I have a 2011 1.4L Eco MT, and used to have a P0420 code. Despite many threads saying otherwise, P0420 does not always indicate a bad catalytic converter. I wanted to discuss the diagnostic process I used and give hope to any Cruze owner with a recurring P0420 code. To diagnose, I used a cheap amazon smoke machine (~$180) and the Torque app on my phone with a bluetooth OBD-II reader to read O2 sensor data. To make a long story short, it was a vacuum leak.
1. First and foremost, I made sure the engine was running correctly, by ensuring there were no misfires and that the injectors and spark plugs were firing as they should. I actually changed the spark plugs and coil pack, but the code still returned.
2. I used a smoke machine to pump smoke directly into the exhaust pipe and looked for any exhaust leaks (especially between the two O2 sensors and around the catalytic converter). I didn't have any exhaust leaks, but they can easily trigger a p0420 code by changing O2 sensor readings.
3. I used a smoke machine to pump smoke directly into the air intake to look for any intake leaks. Air intake leaks can also cause a P0420 code by letting excess air (running lean) into the exhaust and changing O2 sensor readings. In my case, there were 3 intake leaks: One where the intercooler pipe mates with the throttle body (loose hose clamp) and two where the intercooler pipes attach to the intercooler.
4. If you have completed steps 1-3, and you are running good with no intake or exhaust leaks, then you should remove the catalytic converter and visually inspect the inside honeycomb material for damage, blockage, or severe discoloration. If the catalytic converter looks bad, then you have your culprit. If the catalytic converter looks fine, then you need to reinstall the converter and use a scan tool to look at the O2 sensor readings.
5. Check your O2 Sensor readings. After the car is fully warm, sensor 2 should remain relatively flat around 0.4-0.9V while sensor 1 should switch constantly between 0.1V and 0.9V. Check to make sure this holds true at various engine speeds from idle to 3000RPM. If you see sensor 2 switching voltages like sensor 1, then it is likely your catalytic converter has truly failed.
6. If you have finished the diagnosis, and confirmed you have a bad catalytic converter, you must ask yourself why the converter failed (or it will happen again!). Catalytic converters rarely fail on their own, and usually fail due to engine oil/coolant consumption, PCV problems, excessive misfiring, etc. Essentially, a bad catalytic converter is usually the result of another engine problem sending contaminants into your exhaust system. So before replacing your cat, fix your engine so you won't ever have this problem again.
Hopefully this step-by-step process helps you avoid an expensive repair.
- A GM Engineer
UPDATE: 2/3/23
After fixing my vacuum leaks, p0420 stayed off for ~ 4 weeks. I thought my converter was fine and I was in the clear... Wrong! The p0420 code has returned but will only be thrown in specific situations. When the ambient temps are <20F (Really Cold Conditions) AND when I am idling frequently, or in stop-and-go traffic. I have gone through the entire diagnostic process, and I have determined that my catalytic converter is "borderline bad".
I bought my Cruze in 11/22 and it was running very poorly due to neglected PCV system failure (oil everywhere, running lean, misfires). Despite doing extensive engine repair and making sure it is running well, the damage has already been done to my converter. The efficiency of my converter is below the computer's threshold in certain conditions, but still works just fine in 90% of my driving. Since it still works most of the time, and since Michigan does not have emissions testing, I have decided to keep my borderline catalytic converter going and erase the code when it comes up.
1. First and foremost, I made sure the engine was running correctly, by ensuring there were no misfires and that the injectors and spark plugs were firing as they should. I actually changed the spark plugs and coil pack, but the code still returned.
2. I used a smoke machine to pump smoke directly into the exhaust pipe and looked for any exhaust leaks (especially between the two O2 sensors and around the catalytic converter). I didn't have any exhaust leaks, but they can easily trigger a p0420 code by changing O2 sensor readings.
3. I used a smoke machine to pump smoke directly into the air intake to look for any intake leaks. Air intake leaks can also cause a P0420 code by letting excess air (running lean) into the exhaust and changing O2 sensor readings. In my case, there were 3 intake leaks: One where the intercooler pipe mates with the throttle body (loose hose clamp) and two where the intercooler pipes attach to the intercooler.
4. If you have completed steps 1-3, and you are running good with no intake or exhaust leaks, then you should remove the catalytic converter and visually inspect the inside honeycomb material for damage, blockage, or severe discoloration. If the catalytic converter looks bad, then you have your culprit. If the catalytic converter looks fine, then you need to reinstall the converter and use a scan tool to look at the O2 sensor readings.
5. Check your O2 Sensor readings. After the car is fully warm, sensor 2 should remain relatively flat around 0.4-0.9V while sensor 1 should switch constantly between 0.1V and 0.9V. Check to make sure this holds true at various engine speeds from idle to 3000RPM. If you see sensor 2 switching voltages like sensor 1, then it is likely your catalytic converter has truly failed.
6. If you have finished the diagnosis, and confirmed you have a bad catalytic converter, you must ask yourself why the converter failed (or it will happen again!). Catalytic converters rarely fail on their own, and usually fail due to engine oil/coolant consumption, PCV problems, excessive misfiring, etc. Essentially, a bad catalytic converter is usually the result of another engine problem sending contaminants into your exhaust system. So before replacing your cat, fix your engine so you won't ever have this problem again.
Hopefully this step-by-step process helps you avoid an expensive repair.
- A GM Engineer
UPDATE: 2/3/23
After fixing my vacuum leaks, p0420 stayed off for ~ 4 weeks. I thought my converter was fine and I was in the clear... Wrong! The p0420 code has returned but will only be thrown in specific situations. When the ambient temps are <20F (Really Cold Conditions) AND when I am idling frequently, or in stop-and-go traffic. I have gone through the entire diagnostic process, and I have determined that my catalytic converter is "borderline bad".
I bought my Cruze in 11/22 and it was running very poorly due to neglected PCV system failure (oil everywhere, running lean, misfires). Despite doing extensive engine repair and making sure it is running well, the damage has already been done to my converter. The efficiency of my converter is below the computer's threshold in certain conditions, but still works just fine in 90% of my driving. Since it still works most of the time, and since Michigan does not have emissions testing, I have decided to keep my borderline catalytic converter going and erase the code when it comes up.
The code happens a couple times a year.
