1998 GMC Sonoma threw code P1133 02S 1/1

need more info if high mileage on original fuel pump check pressure because if pump is not pumping enough fuel it will not open fuel pressure regulator and will give you same issue

have it tested at autozone ,,it will read your wires for a possible short ..they will read it free

CODE PO155 - HO2S 21 BANK 2 SENSOR 1 HEATER CIRCUIT MALFUNCTION CONDITIONS.CHECK O2 SENSOR FUSE AND WIRING CRCUIT BEFORE BUYING A NEW HO2S.IF SENSOR BAD REPLACE IT.THEN YOU CAN CLEAR THE CODE.

Go to Autozone auto parts and they will connect to the computer and read the code(s) for no fee.

OK, if the scanner can't read codes or communicate with the computer and the service engine soon light does not go on when ignition is turned on but it hasn't started, then the computer may be bad on it.

I have an 03 and mine says 50psi. Check your tire reading.

Even a loose fuel cap or distributor cap can bring up the light . Without codes it will be like shooting in the dark to identify why it is light up. Any fault , anywhere in the car can cause the engine light to come on.
Unless you face any problem in your car dont break your mind over that.

check all the fuses,especially the guages fuse, this also powers the ECM

sound like the O2 sensor or PCV... take the car to autozone and they will use the ODB reader on it for free.I suspect one or the other sensor. How many miles do you have on it?

Pull plug wire and install a philips screwdriver into the plug wire get it 1/4 inch away from a good ground and crank the engine over, is there spark? if so check that you have fuel pressure buy renting a fuel pressure test kit from schucks or auto zone and turn the Key to run position with the gage hooked up, it should read 50 PSI turn key off and wait 20 seconds should still have 20 PSI of fuel pressure, if no fuel pressure check fuel pump relay, then check fuse to pump. if you have a bad relay and are not getting fuel then check the oil pressure switch to see if you have oil pressure at the switch if no pressure then the oil pressure safety switch has died and needs to be replaced and should stark after replacing. If you have fuel then check the timing to see if you slipped timing belt.