Hi. I have codes p0128 and p0420. I need help to understand what each code means and what to do. Thank you scotty and team.
For P0128 troubleshooting see below: will need scan tool
https://www.samarins.com/diagnose/p0128.html
For P0420 troubleshooting see below: will need scan tool
https://carkiller.com/scottykilmer/postid/82370/
Yes, I have noticed the coolant level go to low in about 5 days or so when before it would stay on full for months.
The coolant getting low is a whole different set of problems.
Upsate.. I changed the temperature sensor and it turns out my car didn't have a thermostat, not sure why, and the check engine light turned off and has not turned on yet. Thank you to all for your advice.
I forgot to mention, a new thermostat has been placed and the check engine light turned off.
Thank you for the update (will help others as well) and glad it’s resolved now.
P0128 means the ECM is showing that the engine is not warming up fast enough. You probably need a new temperature sensor. P0420 indicates catalytic converter below efficiency but is probably caused by the pre-heater in the 02 sensor being burnt out. It probably needs replacing; the one nearest the exhaust manifold.
Thank you for your response.