2005 Lincoln LS - Codes

Fault code P0420 and P0128

Yup, those are fault codes alright… A quick internet search would have told you what they mean.

P0420 is telling you the car thinks your catalytic convertor is below efficiency.

The P0128 is telling you the coolant thermostat has a malfunction. In other words, the car thinks it isn’t heating itself up properly. It probably is running cold and may be responsible for the P0420. Fix the P0128 first. Probably a bad thermostat but that is a wild guess since you didn’t tell me hardly anything about your car or problem.

LOL!!! I’ve been researching these codes and reading about them all day long! When I saw your email, I couldn’t remember what I had said! Thank you! I will get the P0128 checked out first. I really got ripped off with this deal. I just purchased this car on Monday, June 8th!!! Well, we live and learn!

By the way, it’s a 2005 Lincoln LS, V8. It would not connect to the PCM during inspection. I researched it and found a guy who suggested that it might be fuses #7 and #18. It was actually #6. I took it back and they replaced it and it connected after that. That’s when I got the two codes. I’m done. You could poke me with a fork!!! Lol.

I’m assuming you did not have this car inspected by a mechanic prior to purchase?


You’re assuming correctly. It was the “old son-in-law/cousin duo” that got me! I’m not very good at lying, but apparently one or both of them are! There were so many red flags, but all I can say is that I’m very disappointed in them and more so in my son-in-law. No, I’m not by any measure rich. I trusted my son-in-law to make sure that I was getting the best deal possible. But, I don’t have time to hang my head and go in over-stress mode. I need to get it up and running or limping or crawling or in a wheel chair! It just needs to get me from point A to point B right now!

Thank you for your words of “wisdom.”

The only wisdom I can offer is to suggest you now take it to a qualified mechanic.

1 Like

How is the coolant level and does your car have the V6 or V8?

It’s possible the 128 code could be caused by a cracked coolant bottle. This is a very common problem and unfortunately (and to the best of my memory) involves removing the driver’s side front wheel and inner fender to access on the models with the V8.

Thank you for your input. I took it to qualified mechanics this morning and they are replacing the bank One Catalytical Converter and the Thermostat Housing Assembly. Hopefully, this will solve the problem.

1 Like

A word to the wise . . .

Do NOT accept the car back until the mechanic can prove to you that the catalytic converter readiness monitor has run to completion and passed with a comfortable margin

Do NOT accept it back with an incomplete catalytic converter readiness monitor

If that means he has to let it sit until the next morning, so that the car meets the parameters for running the readiness monitor, so be it. One more day won’t make a difference

A qualified mechanic would be doing this already, but there are a lot of guys out there who are all talk, but are in reality idiots

Thanks! He told me about the readiness needed for it to pass inspection and the driving that will have to be done to achieve it.

I really appreciate you guys and the affirmation of information received from the mechanics! Thanks again!

1 Like