Brake light and check engine light randomly turns on

WESLEY1213

MEMBER
1992 GMC SONOMA
2.8L
V6
2WD
MANUAL
248,000 MILES

This vehicle has a lot of miles but overall is a good truck. It has all three u-joints bad right now so it shakes between forty five to mph and that is it. Anyway if I drive it for say more than twenty minutes on the highway the check engine light comes on and or the brake light on the dash. Now I know how to check OBD1 and every time I do it flashes a 1.2 so 12 which is system normal. And again the brake light comes on mid drive. I checked the fluid level and it is fine, the e-brake never gets used and it is fully released, and there is no leaks anywhere and it brakes fine and I do not know what to do about both problems. Both of the fuel injectors are old but I have been running Lucas oil fuel system cleaner and it is been better, does not miss at all. So I do not know what the problem is, or if there even is a problem. But I am tired of seeing a Christmas tree on my dash while I drive.

1 Reply

HARRY P

MECHANIC
2,293 POSTS

Code 12 will always flash. It will flash that code three times, and then any codes that are stored three times each, and then it should flash 12 again.

Here is a list of codes for GM: https://www.2carpros.com/articles/buick-cadillac-chevy-gmc-oldsmobile-pontiac-gm-1983-1995-obd1-code-definitions-and-retrieval-method

So if you did not wait to see if other codes come up after the 12, recheck it and let us know what you get.

As far as the brake light goes, I would look at the brake fluid level sensor in the master cylinder. Make sure that the connector is tight and clean, and that the wires are not frayed. If it is not too expensive (which it should not be), get a new sensor. It is pretty common for them to fail.