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.
Mode 03: Interrogating fault memory
Description
When the Engine Control Module (ECM) recognizes an emission related fault, it turns on the Malfunction Indicator Lamp (MIL) or if a Electronic Throttle Malfunction is recognized, the Engine Control Module (ECM) turns on the Electronic Power Control (EPC) Warning Lamp which are both located in the instrument cluster.
Diagnostic Mode 03 is used to retrieve and view any DTC which may be stored in the Engine Control Module (ECM).
The DTCs are sorted by SAE code with the DTC tables consisting of a 5-digit alpha-numeric value.
Depending on scan tool and protocol used, the information displayed in diagnostic mode 03 may be referred to by different names such as Test-ID (TID), Hex-ID, Component-ID (CID), On-Board Diagnostic Monitor Identifier (OBDMID), or contain no name at all and be referenced by only a number.
The following tables provide a breakdown and explanation of the DTC code.
P-Codes
| Component group | |||||
| P | x | x | x | x | DTC for the drivetrain |
| Norm-Code | |||||
| P | 0 | x | x | x | Trouble codes defined by SAE with specified malfunction texts |
| P | 1 | x | x | x | Additional emission relevant DTCs provided by the manufacturer |
| P | 2 | x | x | x | DTCs defined by SAE with specified texts, from MY 2000 |
| P | 3 | x | x | x | Additional emission relevant DTCs provided by the manufacturer from MY 2000 |
| Component group | |||||
| Repair group | |||||
| P | x | 0 | x | x | Fuel and air mixture and additional emission regulations |
| P | x | 1 | x | x | Fuel and air ratios |
| P | x | 2 | x | x | Fuel and air ratios |
| P | x | 3 | x | x | Ignition system |
| P | x | 4 | x | x | Additional exhaust system |
| P | x | 5 | x | x | Speed and idle control |
| P | x | 6 | x | x | Control module and output signals |
| P | x | 7 | x | x | Transmission |
| P | x | 8 | x | x | Transmission |
| P | x | 9 | x | x | Control modules, input and output signals |
U-Codes
| Component group | |||||
| U | x | x | x | x | DTC for network (CAN bus) |
| Norm-Code | |||||
| U | 0 | x | x | x | Trouble codes defined by SAE with specified malfunction texts |
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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.