Test-AC
DM1 Lamp Status and Flash Signals
The DM1 (Diagnostic Message 1) in the J1939 protocol reports active Diagnostic Trouble Codes (DTCs) and controls vehicle warning indicators. It defines the behavior of the Malfunction Indicator Lamp (MIL) and other warning lamps, which can be off, on solid, or flashing, depending on the severity and priority of detected faults. Flashing typically signals a more urgent or severe condition, while a solid light indicates an active but less critical issue.
- PL (Protect Lamp) - DTC's indicate non-electronic subsystem issue.
- AWL(Amber Warning Light) - DTC's indicate a non-critical issue that does not warrant stopping the vehicle.
- RSL(Red Stop Lamp) - DTC's indicate a critical issue that warrants stopping the vehicle immediately.
- MIL(Malfunction Indicator Lamp) - At least one DTC indicates emissions related issue.
DM1 encodes warning lamp information in its first 2 bytes, combining both lamp status and flash behavior. Each lamp is represented by two 2-bit fields—one in byte 1 (status) and one in byte 2 (flash).
Status Values:
- 0 = OFF
- 1 = ON
- 2 = Reserved
- 3 = Not Available
Flash Values:
- 0 = Slow Flash (1 Hz).
- 1 = Fast Flash (2 Hz).
To decode, split each byte into 2-bit segments and map each pair to its corresponding lamp. The final behavior is determined by combining status and flash (e.g., ON + fast flash = rapidly blinking warning).