Monitor status since DTCs cleared
Last reviewed 2026-08-31
Mode 01 · PID 01 (decimal 1)
Description
MIL (check-engine lamp) state, confirmed DTC count, and OBD readiness tests since codes were cleared. Spark vs diesel engines decode bytes C/D differently. Mode 01 only — not freeze frame.
- PID number
- 01 · 1
- Unit
- —
- Range
- —
- Data bytes
- 4
- Formula
- Bit encoded (MIL, DTC count, readiness)
Bit decode map
All engines
| Byte.bit | Field | Role |
|---|---|---|
| A7 | MIL / check-engine lamp 1 = lamp on. | — |
| A0 | DTC count bit 0 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A1 | DTC count bit 1 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A2 | DTC count bit 2 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A3 | DTC count bit 3 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A4 | DTC count bit 4 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A5 | DTC count bit 5 Part of 7-bit confirmed DTC count (A6..A0). | — |
| A6 | DTC count bit 6 Part of 7-bit confirmed DTC count (A6..A0). | — |
| B0 | Misfire monitor — available | availability |
| B1 | Fuel system monitor — available | availability |
| B2 | Comprehensive component monitor — available | availability |
| B3 | Engine type flag 0 = spark ignition, 1 = compression ignition (diesel). | — |
| B4 | Misfire monitor — incomplete | incomplete |
| B5 | Fuel system monitor — incomplete | incomplete |
| B6 | Comprehensive component monitor — incomplete | incomplete |
Spark ignition (byte C/D)
| Byte.bit | Field | Role |
|---|---|---|
| C0 | Catalyst — available | availability |
| C1 | Heated catalyst — available | availability |
| C2 | Evaporative system — available | availability |
| C3 | Secondary air system — available | availability |
| C4 | Gasoline particulate filter — available | availability |
| C5 | Oxygen sensor — available | availability |
| C6 | Oxygen sensor heater — available | availability |
| C7 | EGR system — available | availability |
| D0 | Catalyst — incomplete | incomplete |
| D1 | Heated catalyst — incomplete | incomplete |
| D2 | Evaporative system — incomplete | incomplete |
| D3 | Secondary air system — incomplete | incomplete |
| D4 | Gasoline particulate filter — incomplete | incomplete |
| D5 | Oxygen sensor — incomplete | incomplete |
| D6 | Oxygen sensor heater — incomplete | incomplete |
| D7 | EGR system — incomplete | incomplete |
Compression ignition (byte C/D)
| Byte.bit | Field | Role |
|---|---|---|
| C0 | NMHC catalyst — available | availability |
| C1 | NOx/SCR monitor — available | availability |
| C3 | Boost pressure — available | availability |
| C5 | Exhaust gas sensor — available | availability |
| C6 | PM filter monitoring — available | availability |
| C7 | EGR and/or VVT system — available | availability |
| D0 | NMHC catalyst — incomplete | incomplete |
| D1 | NOx/SCR monitor — incomplete | incomplete |
| D3 | Boost pressure — incomplete | incomplete |
| D5 | Exhaust gas sensor — incomplete | incomplete |
| D6 | PM filter monitoring — incomplete | incomplete |
| D7 | EGR and/or VVT system — incomplete | incomplete |
- Bit-encoded or enumerated — not a single scaled physical value.
Defined by SAE J1979 / ISO 15031-5. Public index — not a substitute for the paid SAE document.
Sources
Provenance for this page. Official standards outrank community notes. See the confidence policy.
Official standard · high trust
SAE J1979 / ISO 15031-5 Mode 01 PID formulas (public index)
J1979 public PID index: 01 01