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.
| DTC | Probable Cause |
|---|---|
| 13 | Open Oxygen Sensor Circuit |
| 14 | Coolant Sensor Signal Voltage Low |
| 15 | Coolant Sensor Signal Voltage High |
| 16 | VSS Buffer Fault |
| 21 | TPS Signal Voltage High |
| 22 | TPS Signal Voltage Low |
| 24 | VSS - "C" & "K" Series Except M/T |
| 24 | VSS Transmission Output Signal - With A/T |
| 24 | VSS - With M/T |
| 28 | Transmission Range Pressure Switch |
| 31 | Engine Speed Governor - "G" Series |
| 32 | EGR Circuit Error Backpressure EGR With Solenoid |
| 32 | EGR Circuit Error With EVRV Solenoid |
| 32 | EGR Ckt Error - "C", "G", "K" Series W/ Linear EGR |
| 33 | MAP Sensor Signal Voltage High |
| 34 | MAP Sensor Signal Voltage Low |
| 35 | Idle Speed Error |
| 36 | Idle Speed Actuator FaulT - A/T |
| 37 | TCC Brake Switch On/Off |
| 38 | TCC Brake Switch On/Off |
| 39 | TCC Stuck Off - 4L80-E Transmission |
| 42 | Ignition Control |
| 43 | Knock Sensor Without Spark Module (Dual Sensors) |
| 43 | Knock Sensor Without Spark Module (Single Sensor) |
| 43 | Knock Sensor With Spark Control Module |
| 44 | Lean Exhaust Indicated |
| 45 | Rich Exhaust Indicated |
| 51 | PROM Error (Faulty Or Incorrect PROM) |
| 52 | Faulty CALPAK |
| 52/53 | System Voltage High |
| 54 | Fuel Pump Circuit |
| 55 | ECM/PCM Error |
| 58 | Transmission Fluid Temperature High |
| 59 | Transmission Fluid Temperature Low |
| 66 | 3-2 Control Solenoid Ckt Fault 4L60-E Transmission |
| 67 | TCC Solenoid Circuit Check - 4L60-E Transmission |
| 68 | Overdrive Ratio Error - 4L80-E Transmission |
| 69 | Torque Converter Clutch Stuck On 4L60-E Transmission |
| 69 | Torque Converter Clutch Stuck On 4L80-E Transmission |
| 72 | VSS Circuit Loss Transmission Output Signal |
| 73 | Pressure Control Solenoid (Current Error) |
| 74 | Transmission Input Speed Error 4L80-E Transmission |
| 75 | System Voltage Low |
| 79 | Transmission Fluid Temperature High |
| 81 | Transmission 2-3 Error |
| 82 | Transmission 1-2 Error |
| 83 | TCC Solenoid Circuit Fault |
| 85 | Undefined Gear Ratio |
| 86 | Low Gear Ratio Error |
| 87 | High Gear Ratio 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.