Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Reading Trouble Codes
The control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual control module and sensor/solenoid connector terminals with a digital voltmeter. Some models REQUIRE a scan tester to pull trouble codes. See SCAN TESTER DATA and SCAN TESTER USAGE .
If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.
| Code | Probable Cause |
|---|---|
| 12 | No Engine Speed Sensor Reference Pulse |
| CODE 13 | Open Oxygen Sensor Circuit |
| CODE 14 | Coolant Sensor Signal Voltage Low |
| CODE 15 | Coolant Sensor Signal Voltage High |
| CODE 16 | VSS Buffer Fault |
| CODE 21 | TPS Signal Voltage High |
| CODE 22 | TPS Signal Voltage Low |
| CODE 23 | Intake Air Temperature Low |
| CODE 24 | Vehicle Speed Sensor - M/Tt |
| CODE 24 | VSS Transmission Output Signal A/T |
| CODE 25 | Intake Air Temperature High |
| CODE 28 | Transmission Range Pressure Switch |
| CODE 32 | EGR Circuit Error Backpressure Egr With Solenoid |
| CODE 32 | EGR Circuit Error With Linear EGR |
| CODE 33 | MAP Sensor Signal Voltage High |
| CODE 34 | MAP Sensor Signal Voltage Low |
| CODE 35 | Idle Speed Error |
| CODE 37 | TCC Brake Switch On/Off |
| CODE 38 | TCC Brake Switch On/Off |
| CODE 41 | 1X Signal Error |
| CODE 42 | Ignition Control |
| CODE 43 | Knock Sensor Without Spark Module (Dual Sensors) |
| CODE 43 | Knock Sensor Without Spark Module (Single Sensor) |
| CODE 44 | Lean Exhaust Indication |
| CODE 45 | Rich Exhaust Indication |
| CODE 51 | PROM Error (Faulty Or Incorrect PROM) |
| CODE 52 | Faulty CALPAK |
| CODE 52 | System Voltage High |
| CODE 53 | System Voltage High |
| CODE 54 | Fuel Pump Circuit |
| CODE 55 | ECM/PCM Error |
| CODE 58 | Transmission Fluid Temperature High |
| CODE 59 | Transmission Fluid Temperature Low |
| CODE 66 | 3-2 Control Solenoid Ckt Fault 4L60-E Transmission |
| CODE 67 | TCC Solenoid Circuit Check - 4L60-E Transmission |
| CODE 69 | Torque Converter Clutch Stuck On 4L60-E Transmission |
| CODE 72 | VSS Circuit Loss Transmission Output Signal |
| CODE 73 | Pressure Control Solenoid (current Error) |
| CODE 75 | System Voltage Low |
| CODE 79 | Transmission Fluid Temperature High |
| CODE 81 | Transmission 2-3 Error |
| CODE 82 | Transmission 1-2 Error |
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.