To get the check engine codes to flash in your dash panel, use a jumper wire or a paper clip and connect terminals A and B of the diagnostic connector. Turn your ignition key on with engine off and the codes should start to blink. All codes should start with code 12 which is one long flash followed by 2 short flashes.
This code 12 means the diagnostic system is normal and will repeat itself continuously if there are no trouble codes. Otherwise, code 12 will flash 3 times before flashing the fault codes.
Below are the OBD DTC's for 1995-previous model year EFI-equipped GM vehicles.
DTC - 12 No distributor reference pulse (diagnostic test active)
DTC - 13 Oxygen sensor circuit open or no activity
DTC - 13 Left bank O2 sensor circuit open or no activity
DTC - 14 Engine coolant temp sensor error (high temp indicated)
DTC - 15 Engine coolant temp sensor error (low temp indicated)
DTC - 16 System voltage too low
DTC - 17 Camshaft position sensor error
DTC - 21 Throttle Position sensor error (signal high)
DTC - 22 Throttle position sensor error (signal low)
DTC - 23 Intake air temp sensor error (low temp indicated)
DTC - 24 Vehicle speed sensor error (open circuit or no activity)
DTC - 25 Intake air temp sensor error (high temp indicated)
DTC - 26 Quad Driver Module (QDM A) error
DTC - 28 Auto transmission range pressure switch error
DTC - 31 Wastegate solenoid circuit error
DTC - 31 Gear Position Switch (PRNDL) error
DTC - 32 EGR system failure
DTC - 33 MAP sensor circuit error (signal high indicating low vacuum)
DTC - 34 MAP sensor circuit error (signal low indicating high vacuum)
DTC - 35 IAC problem or idle error
DTC - 36 MAF sensor error
DTC - 36 24x Crankshaft position sensor circuit error
DTC - 36 4T60-E Shifting Error
DTC - 37 TCC brake switch circuit error
DTC - 38 TCC brake switch circuit error
DTC - 39 Clutch switch circuit error
DTC - 39 TCC error
DTC - 41 Ignition control error
DTC - 41 MEM-CAL error
DTC - 41 C³I Cam Sensor Signal error
DTC - 42 Ignition bypass circuit error
DTC - 43 Knock sensor error
DTC - 44 Oxygen sensor error (lean condition indicated)
DTC - 44 Left bank O2 sensor error (lean condition indicated)
DTC - 45 Oxygen sensor error (rich condition indicated)
DTC - 45 Left bank O2 sensor error (rich condition indicated)
DTC - 46 Pass-Key II (VATS) system error - circuit out of freq range
DTC - 47 UART (serial data) circuit error
DTC - 51 PROM error
DTC - 51 Incorrect MEM-CAL
DTC - 52 Fuel cal-pak incorrect or missing
DTC - 53 System voltage too high
DTC - 53 Digital EGR Valve solenoid 1 error
DTC - 54 Fuel pump circuit low voltage
DTC - 54 Digital EGR Valve solenoid 2 error
DTC - 55 ECM error
DTC - 55 Digital EGR Valve solenoid 3 error
DTC - 56 Quad Driver Module (QDM B) error
DTC - 57 Boost Control error
DTC - 58 Trans fluid temp sensor circuit error (low voltage)
DTC - 58 VATS system error
DTC - 59 Trans fluid temp sensor circuit error (high voltage)
DTC - 61 A/C system performance
DTC - 63 Right bank O2 sensor circuit error
DTC - 63 MAP sensor circuit signal voltage high (low vacuum indicated)
DTC - 64 Right bank O2 sensor lean exhaust indicated
DTC - 64 MAP sensor circuit signal voltage low (high vacuum indicated)
DTC - 65 Right bank O2 sensor rich exhaust indicated
DTC - 66 A/C pressure sensor circuit error (low pressure indicated)
DTC - 67 A/C pressure sensor circuit error
DTC - 68 A/C clutch relay circuit error (shorted to ground)
DTC - 69 A/C clutch relay circuit error (open circuit indicated)
DTC - 69 A/C high pressure switch error
DTC - 70 A/C pressure sensor circuit error (high pressure indicated)
DTC - 71 A/C evaporator temp sensor circuit error (low temp indicated)
DTC - 72 VSS signal circuit error
DTC - 73 A/C evaporator temp sensor circuit error (high temp indicated)
DTC - 75 Digital EGR solenoid #1 circuit error
DTC - 76 Digital EGR solenoid #2 circuit error
DTC - 77 Digital EGR solenoid #3 circuit error
DTC - 79 Transmission fluid overtemp
DTC - 80 Transmission component slipping
DTC - 82 3x Crankshaft position sensor circuit error
DTC - 85 PROM error
DTC - 86 A/D error
DTC - 87 EEPROM error (flash memory error)
DTC - 90 TCC error
DTC - 93 Transmission pressure control solenoid circuit error
DTC - 96 Transmission system voltage low
DTC - 98 Invalid PCM program
DTC - 99 Invalid PCM program
