Reading Codes/OBD1-Pre 1996 Models

1) Locate ADL port below dash.
2) Insert paperclip or similar wire. (see photo)
3) KOEO (Key On Engine Off) watch SES light.
4) SES (check engine) light will blink out codes. It will flash, then short pause, then flash again, then long pause between codes. Example: flash, (pause), flash, flash (long pause) is code12 for no RPM. This code is always present.

Example 2: Flash, flash, flash (pause) flash, flash, flash, (long pause) = code 33. The computer will continue to scroll through the codes and generally begins and ends with 3 code 12’s, with important codes being shown in between.

NOTE: All DTC(S) with the * sign are automatic transmission (4L80E) related

DTC 13 – Engine Shutoff Solenoid Circuit Fault
DTC 14 – Engine Coolant Temperature (ECT) Sensor Circuit Low (High Temp Indicated)
DTC 15 – Engine Coolant Temperature (ECT) Sensor Circuit High (Low Temp Indicated)
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 (Response Time Short)
DTC 36 – Injection Pulse Width Error (Response 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 Indicated)
DTC 43 – Fuel Temperature Circuit High (Low Temp Indicated)
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 Indicated)
DTC 48 – Intake Air Temperature Sensor Circuit High (Low Temp Indicated)
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 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 – 2-3 Shift Solenoid Circuit Fault
*DTC 82 – 1-2 Shift Solenoid Circuit Fault
*DTC 83 – TCC PWM Solenoid Circuit Fault
*DTC 84 – Accelerator Pedal Position Circuit Fault
*DTC 85 – Undefined Ratio Error
*DTC 86 – Low Ratio Error
*DTC 87 – High Ratio Error
DTC 88 – TDC (Top Dead Center) Offset Error
DTC 91 – #1 Cylinder Balance Fault
DTC 92 – #2 Cylinder Balance Fault
DTC 93 – #3 Cylinder Balance Fault
DTC 94 – #4 Cylinder Balance Fault
DTC 95 – #5 Cylinder Balance Fault
DTC 96 – #6 Cylinder Balance Fault
DTC 97 – #7 Cylinder Balance Fault
DTC 98 – #8 Cylinder Balance Fault
DTC 99 – Accelerator Pedal Position 2 (5 Volt Reference Fault)