Originally posted by Turbine Doc:

More for the FAQs please feel free to add any I've missed.

OBD-I is pre 96 vintage truck coding use OBD-II for trucks of 96 & later years & requires a scan tool to read them.


The Data Link connector is located below the steering wheel lower left rim of the dash just about knee cap height.


Use a jumper (paperclip, etc) to connect these terminals. The connection/removal of the jumper between terminals (A&B) should be done with the ignition switch OFF. Also to prevent potential volt spike to PCM remove clip with Key OFF also.Once jumper is installed then turn key to on/run (not full start) to begin the flashing sequence


The Service Engine Soon light will flash Code 12 three times to indicate that the diagnostics are working. Trouble codes will then follow, one at a time, three times each. DTC 12 will only appear if there are no other codes.


2 The codes appear in numerical order, and each code repeats itself three times before the next begins. This is different from some other ECM's.


3. It is helpful to the diagnostic process to know when codes are setting, particularly if there is more than one. Hence, clearing the codes is something you may wish to do. Clearing the codes may be accomplished by simultaneously depressing the brake and accelerator pedals fully while the PCM is in diagnostic mode (terminals A and B connected). It will not appear that you have cleared the codes until the next time you power up in diagnostic mode, however.

DTC 12 - No Codes Present
DTC 13 - Engine Shutoff Solenoid Circuit Fault
DTC 14 - Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temp)
DTC 15 - Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp)
DTC 16 - Vehicle Speed Sensor Buffer Fault
DTC 17 - High Resolution Circuit Fault
DTC 18 - Pump Cam Reference Pulse Error
DTC 19 - Crankshaft Position Reference Error
DTC 21 - Accelerator Pedal Position 1 Circuit High
DTC 22 - Accelerator Pedal Position 1 Circuit Low
DTC 23 - Accelerator Pedal Position 1 Circuit Range Fault
DTC 24 - Vehicle Speed Sensor Circuit Low (Output Speed Signal)
DTC 25 - Accelerator Pedal Position 2 Circuit High
DTC 26 - Accelerator Pedal Position 2 Circuit Low
DTC 27 - Accelerator Pedal Position 2 Circuit Range Fault
DTC 28 - Transmission Range Pressure Switch Circuit
DTC 29 - Glow Plug Relay Fault
DTC 31 - EGR Control Pressure/Baro Sensor Circuit Low (High Vacuum)
DTC 32 - EGR Circuit Error
DTC 33 - EGR Control Pressure/Baro Sensor Circuit High
DTC 34 - Injection Timing Stepper Motor Fault
DTC 35 - Injection Pulse Width Error (Time Short)
DTC 36 - Injection Pulse Width Error (Time Long)
DTC 37 - TCC Brake Switch Stuck "ON"
DTC 38 - TCC Brake Switch Stuck "OFF"
DTC 39 - TCC Stuck "OFF"
DTC 41 - Brake Switch Circuit Fault
DTC 42 - Fuel Temperature Circuit Low (High Temp)
DTC 43 - Fuel Temperature Circuit High (Low Temp)
DTC 44 - EGR Pulse Width Error
DTC 45 - EGR Vent Error
DTC 46 - Malfunction Indicator Lamp (MIL) Circuit Fault
DTC 47 - Intake Air Temperature Sensor Circuit Low (High Temp )
DTC 48 - Intake Air Temperature Sensor Circuit High (Low Temp )
DTC 49 - Service Throttle Soon Lamp Circuit Fault
DTC 51 - PROM Error
DTC 52 - System Voltage High Long
DTC 53 - System Voltage High
DTC 54 - PCM fuel circuit error
DTC 56 - Injection Pump Calibration Resistor Error
DTC 57 - PCM 5 Volt Shorted
DTC 58 - Transmission Fluid Temp Circuit Low
DTC 59 - Transmission Fluid Temp Circuit High
DTC 61 - Turbo Boost Sensor Circuit High
DTC 62 - Turbo Boost Sensor Circuit Low
DTC 63 - Accelerator Pedal Position 3 Circuit High
DTC 64 - Accelerator Pedal Position 3 Circuit Low
DTC 65 - Accelerator Pedal Position 3 Circuit Range Fault
DTC 66 - 3-2 Shift Control Solenoid
DTC 67 - TCC Solenoid Circuit (Open or Short)
DTC 68 - Transmission Component Slipping
DTC 69 - TCC Stuck "ON"
DTC 71 - Set/Coast Switch Fault (Cruise Control)
DTC 72 - Vehicle Speed Sensor Circuit Loss (Output Speed Signal)
DTC 73 - Pressure Control Solenoid Circuit (Current Error)
DTC 74 - Transmission Input Speed (TIS) Sensor Circuit
DTC 75 - System Voltage Low
DTC 76 - Resume/Accel Switch Fault (Cruise Control)
DTC 78 - Turbo Wastegate Solenoid Fault
DTC 79 - Transmission Fluid Over Temperature
DTC 81 - Transmission 2-3 Shift Solenoid Circuit
DTC 82 - Transmission 1-2 Shift Solenoid Circuit
DTC 83 - Torque Converter Clutch
DTC 85 - Transmission Gear
DTC 86 - Transmission Gear Ratio Error
DTC 87 - Transmission Gear Ratio Error
DTC 88 - Top Dead Center Offset Problem
DTC 91 thru 98 - Cylinder Balance
DTC 99 - Accelerator Pedal Position Sensor 5-Volt Reference Problem

OBDII codes:

ODB II Diagnostic codes OBDII compliant reader required to access codes.


Not all codes show as "hard codes" that light the SES light, some are stored in the history as discrete faults</DIR>


P0101 Mass Air Flow (MAF) System Performance


P0102 MAF Sensor Circuit Low Frequency


P0103 MAF Sensor Circuit High Frequency


P0112 Intake Air Temperature (IAT) Sensor Circuit Low Voltage


P0113 IAT Sensor Circuit High Voltage


P0117 Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage


P0118 ECT Sensor Circuit High Voltage


P0123 Accelerator Pedal Position (APP) Sensor 1 Circuit Performance


P0122 APP Sensor 1 Circuit Low Voltage


P0123 APP Sensor 1 Circuit High Voltage


P0126 Insufficient ECT for Stable Operation


P0182 Fuel Temperature Sensor Circuit Low Voltage


P0183 Fuel Temperature Sensor Circuit High Voltage


P0215 Engine Shut-Off Control Circuit


P0216 Injection Timing Control Circuit


P0219 Engine Over-speed Condition


P0220 APP Sensor 2 Circuit


P0221 APP Sensor 2 Circuit Performance


P0222 APP Sensor 2 Circuit Low Voltage


P0223 APP Sensor 2 Circuit High Voltage


P0225 APP Sensor 3 Circuit


P0226 APP Sensor 3 Circuit Performance


P0227 APP Sensor 3 Circuit Low Voltage


P0228 APP Sensor 3 Circuit High Voltage


P0231 Fuel Pump Feedback Circuit Low Voltage


P0236 Turbocharger Boost System


P0237 Turbo Boost Sensor Circuit Low Voltage


P0238 Turbo Boost Sensor Circuit High Voltage


P0251 Injection Pump Cam System


P0263 Cylinder 1 Balance System


P0266 Cylinder 2 Balance System


P0269 Cylinder 3 Balance System


P0272 Cylinder 4 Balance System


P0275 Cylinder 5 Balance System


P0278 Cylinder 6 Balance System


P0281 Cylinder 7 Balance System


P0284 Cylinder 8 Balance System


P0300 Engine Misfire Detected


P0301 Cylinder 1 Misfire Detected


P0302 Cylinder 2 Misfire Detected


P0303 Cylinder 3 Misfire Detected


P0304 Cylinder 4 Misfire Detected


P0305 Cylinder 5 Misfire Detected


P0306 Cylinder 6 Misfire Detected


P0307 Cylinder 7 Misfire Detected


P0308 Cylinder 8 Misfire Detected


P0335 Crankshaft Position (CKP) Sensor Circuit


P0370 Timing Reference High Resolution


P0380 Glow Plug Circuit Performance


P0400 Exhaust Gas Recirculation (EGR) Flow Malfunction


P0401 EGR Flow Insufficient


P0402 EGR Flow Excessive


P0404 EGR System Performance


P0405 EGR Sensor Circuit Low Voltage


P0406 EGR Sensor Circuit High Voltage


P0501 Vehicle Speed Sensor Circuit (VSS)


P0567 Cruise Resume Circuit


P0568 Cruise Set Circuit


P0571 Cruise Brake Switch Circuit


P0601 Internal Control Module Memory


P0602 Control Module Programming


P0604 Control Module RAM Check Sum


P0606 PCM Internal Communications Interrupted


P1125 Accelerator Pedal Position System


P1191 Intake Air Duct Leak


P1214 Injection Pump Timing Offset


P1216 Fuel Solenoid Response Time Short


P1217 Fuel Solenoid Response Time Long


P1218 Injection Pump Calibration Circuit


P1406 EGR Valve Position


P1409 EGR Vacuum System Leak


P1621 EEPROM Write


P1626 Vehicle Theft Deterrent (VTD) Controller Serial Data Circuit


P1627 A/D Performance


P1630 Theft Deterrent PCM in Learn Mode


P1631 Theft Deterrent Password Incorrect


P1635 5 Volt Reference Low


P1641 Malfunction Indicator Lamp (MIL) Control Circuit


P1643 Wait To Start Lamp Control Circuit


P1653 EGR Vent Solenoid Control Circuit


P1654 Service Throttle Soon Lamp Control Circuit


P1655 EGR Solenoid Control Circuit


P1656 Wastegate Solenoid Control Circuit


U1026 Loss of ATC Class 2 Co