OtoDünyam
DEEP TECHNICAL CONTENT

How OBD-II works

How OBD-II works: OBD-II uses a 16-pin DLC; on CAN-based vehicles pin 6 is CAN-H, pin 14 CAN-L, pin 16 battery positive and pins 4/5 are ground references. The page also includes a worked example and measurement sequence.

6 concrete technical facts1 worked example3 sources

Technical frame

How OBD-II works: OBD-II uses a 16-pin DLC; on CAN-based vehicles pin 6 is CAN-H, pin 14 CAN-L, pin 16 battery positive and pins 4/5 are ground references. The page also includes a worked example and measurement sequence.

The technical values here expose the standard, protocol or physical relationship directly; model-specific service values are linked through the matching model/variant dossier.

The goal is not only to define the term but to let the reader calculate and interpret what the data means in a scan, scope or physical test.

Concrete technical facts

  • OBD-II uses a 16-pin DLC; on CAN-based vehicles pin 6 is CAN-H, pin 14 CAN-L, pin 16 battery positive and pins 4/5 are ground references.
  • Mode 01 PID 0C engine speed is two bytes and RPM = ((A × 256) + B) / 4.
  • Mode 01 PID 05 engine-coolant temperature uses °C = A − 40.
  • P0xxx codes are generally standardized while P1xxx can be manufacturer-specific; the code text alone does not prove root cause.
  • Pending, confirmed and permanent states are not equivalent, and freeze-frame data preserves the original fault condition.
  • Diagnosis should combine operating condition, companion codes, commanded/actual values and physical measurement instead of jumping from code to part.

Worked example

  • PID 0C example: A=0x1F (31) and B=0x40 (64) gives ((31×256)+64)/4 = 2000 rpm.

Measurement and verification sequence

  • Record DTC status/freeze-frame before clearing.
  • Check DLC power and grounds under load.
  • Separate protocol/ECU communication faults from application DTCs.
  • Compare PIDs with independent physical measurement where possible.

Fault-separation logic

  • Is a valid command present and are power/ground/network healthy?
  • Does feedback follow the command?
  • Does an independent physical measurement confirm the output?
  • Is the fault limited to a specific temperature/load/speed condition?
  • Does the result remain stable when the original condition is repeated after repair?

Technical sources

  1. SAE mobility standards catalogue
  2. NHTSA vehicle data and diagnostic context
  3. SAE International · vehicle standards

Continue investigating

Model-specific real technical data · Measurement references · Technical diagnostic atlas