Hi,

Does your engine use an EGR valve?
If it’s not getting turned on in a timely manner it will trip an engine light.

There’s a electric valve that controls vacuum to the EGR valve and it gets plugged up from being able to vent. When this happens the EGR temperature sensor doesn’t send a “change in signal” response to the ECU and that trips on the check engine light.

There is a piece of foam rubber under the vent area cap on top that rots.
A change in the material from moisture or temperature affects the venting.

I replace mine with a piece of polyester fuzz or pillow stuffing. Polyester doesn’t rot.
It can still get dirty and I have only change mine once again more in the 17 years. I have own that 1991 car. It now with 100,000 more miles! 284K and still counting!
It was sold to me because the young lady kept chasing the light and her Indy kept guessing at her expense. She wanted a Mazda Van for her expanding family.

I found the problem after it wouldn’t smog because of the light came on while going to get the certificate!
When bought the car, it didn’t have a light on because “they,” an associate helping her show the car, kept pulling the battery wire off from the little box on the left fender, just before it was test driven each time!

Since this was my first 240 with a CEL, I didn’t really understand the codes so I cannot sat what it was.
Since then I have come to realize that those codes are so generic it almost laughable!
I call it a shotgun blast to a side of a barn!
Yes, you will hit the barn, but in so many places, you’ll learn how sneak up on the most dense spots!

Don’t get to caught up into the code number!

Phil