Service Interaction Protocol
Clear Diagnostic Information
Permanent DTCs: This service does not clear OBD-II permanent DTCs. Those require 3 consecutive successful drive cycles after the fault is repaired.
Overview
“The client uses this service to clear one or more units of diagnostic information from the server’s memory. This includes DTCs, captured data, and status counters.”
Message Format
Byte | Field | Value | Description |
|---|---|---|---|
| 0 | SID | 0x14 | Clear Diagnostic Information |
| 1 | GroupOfDTC (High) | 0x00–0xFF | DTC Group Mask — High Byte |
| 2 | GroupOfDTC (Mid) | 0x00–0xFF | DTC Group Mask — Middle Byte |
| 3 | GroupOfDTC (Low) | 0x00–0xFF | DTC Group Mask — Low Byte |
Byte | Field | Value | Description |
|---|---|---|---|
| 0 | Response SID | 0x54 | Positive Response (SID + 0x40) — single byte, no echo |
Clears all diagnostic info including DTCs, freeze frames, and extended data.
Request
14 FF FF FFTargets only OBD-II/Emissions related faults.
Request
14 00 00 00Targeting only P-codes (implementation dependent).
Request
14 FF FF 00Targeting only communication U-codes.
Request
14 C0 00 00Workflow & Response Pending
Clearing memory (writing to EEPROM or Flash) can be slow. If the operation exceeds ~50ms, the ECU sends NRC 0x78 (Response Pending) to prevent tester timeout. Multiple 0x78 responses may be sent before the final 0x54.
ECU is ready. DTC memory is intact. Diagnostic session active (Default or Extended). Awaiting service request.
Request Processing Flow
Every clear request is validated through a structured 7-gate pipeline before the memory erase operation begins. Each gate has a specific NRC for failure.
54 — single byte, no sub-function echo. DTC memory cleared. Timer reset.Click any step to expand validation logic.
Negative Response Codes
EXCEPTION_MATRIX_V3
The request was not exactly 4 bytes long (SID + 3 bytes).
This negative response indicates a failure in processing the Clear DTCs request. Ensure all pre-conditions and active sessions match the requirements defined by ISO 14229.
State Machine & Security
The ECU transitions through a defined sequence of states during a clear operation. Security state affects whether the operation proceeds or returns NRC 0x33.
ECU is ready. DTC memory is intact. Diagnostic session active (Default or Extended). Awaiting service request.
Service Dependencies & Sessions
0x10SESSION0x27LOCK0x3EPING0x19READ0x85GATE0x28BUS0x22SENS0x31TESTClick any service card to see usage details.
0x01Some groups may be restricted
0x02Service entirely blocked
0x03Full access to all groups
0x04Limited group access only
What Gets Cleared & Preserved
SID 0x14 clears specific memory regions within the targeted GroupOfDTC range. Configuration, security, and adaptive data are always preserved.
Click any item to see detailed explanation.
Memory Management
Understanding EEPROM/Flash layout helps diagnose clearing failures and explains why some data survives a clear operation while other data does not.
Click any segment in the bar to inspect the memory region.
Click any step to see its detailed description.
Common Testing Scenarios
Five real-world test cases. Select a scenario, then press Play or step frame-by-frame with ›. Hover any frame to copy its hex bytes.
Extended session · vehicle stationary · no active faults
3 DTCs erased, memory verified empty
Service Interaction Workflows
Animated workflow runner showing how SID 0x14 integrates with other services. Select a scenario and press Simulate to see the full byte-level interaction.
Complete technician sequence: diagnose → physical repair → clear → verify clean.
Full Workflow · 10 frames10 03Enter Extended Session50 03Session Confirmed19 02 AFRead All Active DTCs59 02 AF …DTCs Returned14 FF FF FFClear All DTCs7F 14 78Response Pending54Clear Complete19 02 AFVerify Empty59 02 AF 00No DTCsPress Simulate to animate the full message sequence.
Troubleshooting & Debugging
Interactive diagnostic checklist and issue cards for common clear failures. Work through the checklist systematically before escalating.
DTCs ReturnCRITICALDTCs reappear immediately after successful 0x54
0x22HIGHNRC 0x22 — Conditions Not Correct
0x33HIGHNRC 0x33 — Security Access Denied
0x13MEDNRC 0x13 — Incorrect Message Length
0x31LOWNRC 0x31 — Request Out of Range
0x72HIGHNRC 0x72 — General Programming Failure
Best Practices & Quick Reference
Immediate 0x54
May send 1× NRC 0x78
1–3× NRC 0x78
3–10+ NRC 0x78
NRC 0x78 is not an error. It signals “processing — keep waiting.” Reset P2* timer (5000ms) on every 0x78 received and continue until 0x54 or a real error NRC arrives.
0x130x220x310x330x720x780x54