2002 Toyota Highlander Check Engine light

HIGHLANDER 02

MEMBER
2002 TOYOTA HIGHLANDER
4 CYL
2WD
AUTOMATIC
12,000 MILES

I recently had a major service done. At the time the CEL was on and when they ran a diagnostic the code came up P0128. Thermostat needed replaced. All maintenance was done and CEL turned off. The next day after driving in the rain on the highway for 120 miles the CEL came on again. I was unable to go back to the same dealer so I went to another place and got a free diagnostic check now they say it is code #P0420. What is it and why would it come on so soon after a dianostic and major tune up? My Highlander has always been serviced regularly and has great gas mileage and has always run smoothly. Any suggestions on what to do? I do not want to pour money into something that is unnecessary. Thanks so much for your help

1 Reply

JAM1234

MEMBER
1 POST

I got the same code driving a few weeks ago - on a road trip of about 1000 miles. I had used 89 octane gas that morning (normally use only 87) - went to Autozone and found that code. At next gas fill up on the way I went to Texaco and put some 87 octane in, pulled the battery cable for 5 minutes and 1000 miles later no light has come back on. Hoping it wasn't a cat for me but just a fluke. What did you end up finding out about your Highlander? Was it a cat? O2 sensor? Fluke? Any help would be appreciated!

My car has been well maintained as well - synthetic oil only, always done fluids etc. On time with dealer only parts and it's garage kept, in Florida.