Check engine light wont go off

there are about a dozen O2 sensor codes. Tell us which one you have

Best bet is to plug it into a code reader to see what the computer believes the problem to be. Only takes a few seconds and should be next to nothing in cost. Best guess is that the front O2 sensor in your air intake needs replacement. Other possibilities are clogged fuel filter or even worn out spark plugs. Need that code number to pin it down accurately.

1991 is pre-OBD2. code readers will not work.
sorry.
however, all is not lost. Many cars have an alternate way of reading codes from the computer.
Toyota has a block under the hood and you short couple wires together and count engine light flashes
Chrysler you can turn the ignition key on and off a few times and count engine light flashes
in your case for GMs from 1982 to 1995
1: find the 12 pin connector under the dash and short the upper two rightmost terminals.
with the ignition "ON" and engine not running. The system will enter the diagnostic mode. In this mode, the computer will display a Code 12, three consecutive times, by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" or light. A Code 12 consists of one flash, a short pause, then two flashes in rapid succession.
2:. After Code 12 is displayed, any stored trouble codes will be displayed by flashing the "CHECK ENGINE", "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR LAMP" light. All codes are displayed 3 times each then a code 12 will repeat. In the diagnostic mode, the computer will also energize all computer controlled relays and solenoids.

Tech -- GM 2 Digit codes for 82 and up (non OBD-II)
code - code definition
12- diagnostic mode
13- 02 sensor or circuit
14- coolant sensor or circuit/ high temp indicated
15- coolant sensor or circuit/ low temp indicated
16- system voltage out of range
19- crankshaft position sensor or circuit
21- throttle position sensor or circuit- voltage high
22- throttle position sensor or circuit- voltage low
23- mixture control (m/c) solenoid or circuit (carbureted models)
23- manifold air temperature (mat) sensor or circuit (1990 and earlier models)
23- intake air temperature (iat) sensor circuit (fuel-injected models)
24- vehicle speed sensor (vss) or circuit
25- manifold air temperature (mat) sensor or circuit - high temperature indicated (1990 and earlier models)
25- intake air temperature (iat) sensor or circuit - high temperature indicated (1991 and later models)
26- quad driver module circuit
27- quad driver module circuit
28- quad driver module circuit
29- quad driver module circuit
31- park/neutral position (pnp) switch circuit
32- baro sensor or circuit (carbureted models)
32- egr circuit (fuel-injected models)
33- manifold absolute pressure (map sensor signal voltage high
33- mass air flow (maf) sensor or circuit - excessive airflow indicated
34- manifold absolute pressure (map) sensor signal voltage low 34- mass air flow (maf) sensor signal - low airflow indicated
35- idle speed control (isc) switch or circuit (shorted) (carbureted models)
35- idle air control (iac) valve/ circuit
38- brake switch circuit
39- torque converter clutch (tcc) circuit
41- no distributor signals to ecm, or faulty ignition module ( carbed models)
41- cylinders select error- mem-cal or ecm problem ( fuel-injected models
41- cam sensor circuit (3.8 engine)
42- bypass or electronic spark timing (est) circuit
43- low voltage at ecm terminal l (carbureted models)
43- knock sensor circuit
44- oxygen sensor or circuit - lean exhaust detected
45- oxygen sensor or circuit - rich exhaust detected
46- power steering pressure switch circuit
48- misfire diagnosis
51- prom, mem-cal or ecm problem
52- calpak or ecm problem
53- egr fault (carbureted models only)
53- system over-voltage (ecm over 17.7 volts)
54- mixture control (m/c) solenoid or circuit (carbureted models)
54- fuel pump circuit (1986 and later models)
55- oxygen sensor circuit or ecm
55- fuel lean monitor (2.2l engine)
61- oxygen sensor signal faulty (possible contaminated sensor)
62- transaxle gear switch signal circuits
63- manifold absolute pressure (map) sensor voltage high (low vacuum detected)
64- manifold absolute pressure (map) sensor voltage low (high vacuum detected)
66- pressure sensor or circuit air conditioning

Did it occur the MAF (will not set code) is defective or the fuel pressure is low?

Is your gas cap on tight? Could be low fuel pressure. Can you check your fuel pressure? Have you checked your fuel filter? You may need to replace the fuel pressure regulator. Locate it and pull vac hose off of it and if there is gas coming out of hose replace regulator. You will need to relieve pressure before changing.

the sensor is getting to much power test and check all power connections and lines for damage /grounding or corrosion

poor start, very poor gas millage

Trouble Code: P0102


MAF Sensor Circuit Low Input
Possible Causes:



Check for leaks between MAF sensor and throttle valve control module Voltage supply faulty. Sensor power circuit open from fuel pump relay to MAF sensor Sensor signal circuit open (may be disconnected) from ECM and MAF Faulty ground cable resistance between connector terminal 1 and Ground MAF Sensor malfunction Sure hope this helped you and good luck.

p1633 is keep alive power voltage to low!! check voltage from alternator to battery, as well as all wires also.make sure battery terminals are not corroded. when car is running, voltage to battery should be 13.5 to14.5, when off voltage at battery should be 12.0 to 12.6,

insufficient switching bank 2 sensor 1 that mean the oxygen sensor on the passager side dont change voltage fast enought remove clean it or if it old change it hope it help FIXYA OUR POST thanks pierre