OBD I codes OBD1 Codes Retrieval (Pre-1995 Cars and Trucks) GM 1983-95 vehicles OBD1 codes self-retrieval As the name implies, you can get the codes for GM cars or trucks yourself if the model of your vehicle is made before 1995, this means as soon as you see “check engine light” in your dash, you can get the code in minutes if you want. Shown on the left is a picture of the connector where you get the GM OBD1 code. When you find the adapter connector, use a jumper wire (see red wire above) and connect terminals A and B. Next turn your key on but don't start. Watch your check engine flash the code/s. EXAMPLE: CODE 12: one long flash and two short flashesCODE 13: one long flash and 3 short flashes. Note: code 12 is usually the first code you get and just ignore it.Watch the code after code 12, that's what you need. GM common codes for OBD1 (for vehicles made before 1995) 12 System normal 13 oxygen sensor circuit open 14 coolant sensor high resistance or shorted 15 coolant sensor circuit low or open 16 direct ignition system (DIS) fault in circuit 17 cam position sensor fault 18 crank or cam sensor error 19 crank sensor circuit fault 21 tps sensor out of range 22 tps sensor signal voltage low 23 intake air temp sensor out of range, low 24 vehicle speed (vss) sensor circuit fault 25 air temp sensor sensor out of range, high 26 quad-driver module (computer) circuit #1 fault 27 quad-driver module (computer) 2nd gear circuit 28 quad-driver module (computer) circuit #2 fault 29 quad driver module (computer) 4th gear circuit 31 cam position sensor fault 32 egr circuit fault 33 map sensor signal out of range, high 34 map sensor signal out of range, low 35 idle air control sensor circuit fault 36 ignition system circuit error 38 brake input circuit fault 39 clutch input circuit fault 41 cam sensor circuit fault, igntion control circuit fault 42 electronic spark timing (EST) circuit grounded 43 knock sensor or electronic spark control circuit fault 44 oxygen sensor lean exhaust 45 oxygen sensor rich exhaust 46 pass-key II circuit or ps.pressure switch circuit fault 47 pcm-bcm data circuit 48 misfire diagnosis 51 calibration error, mem-cal, ecm or eeprom failure 52 engine oil temperature circuit, low temperature indicated 53 battery voltage error or egr or pass-key II circuit 54 egr system failure or fuel pump circuit low voltage 55 a/d converter error or pcm not grounded or lean fuel or frounded reference voltage 56 quad-driver module #2 circuit 57 boost control problem 58 vehicle anti-theft system fuel enable circuit 61 a/c system performance or degraded oxygen sensor signal 62 engine oil temperature high temperature indicated 63 oxygen sensor right side circuit open or map sensor out of range 64 oxygen sensor right side lean exhaust indicated 65 oxygen sensor right side rich exhaust indicated 66 a/c pressure sensor circuit low pressure 67 a/c pressure sensor circuit or a/c clutch circuit failure 68 a/c compressor relay circuit failure 69 a/c clutch circuit head pressure high 70 a/c refrigerant pressure circuit high 71 a/c evaporator temperature sensor circuit low 72 gear selector switch circuit 73 a/c evaporator temperature circuit high 75 digital egr #1 solenoid error 76 digital egr #2 solenoid error 77 digital egr #3 solenoid error 79 vehicle speed sensor (vss) circuit signal high 80 vehicle speed sensor (vss) circuit signal low 81 brake input circuit fault 82 ignition control (IC) 3X signal error 85 prom error 86 analog/digital ecm error 87 eeprom error 99 power management