ELM327 returns “?” when requesting multiple Mode 01 PIDs in one command, what batching strategy should SwiftOBD2 use?

[Jad-Taljabini]

• Context:

  • With a minimal PID set (rpm, speed, maf, engineLoad, absoluteLoad) everything works.
  • When I add more PIDs, the adapter starts replying with “?”.

• Repro:

obdService
  .startContinuousUpdates([
    .mode1(.rpm),
    .mode1(.speed),
    .mode1(.coolantTemp),
    .mode1(.controlModuleVoltage),
    .mode1(.throttlePos),
    .mode1(.relativeThrottlePos),
    .mode1(.engineLoad),
    .mode1(.intakeTemp),
    .mode1(.intakePressure),
    .mode1(.barometricPressure),
    .mode1(.maf)
  ])
  .sink { /* ... */ }

• Observed logs:

Sending command: 010C0D05421145040F0B3310
Response: ["?"]
(repeats)

• Notes:
  • The same OBDService via a small set in ViewModel works fine.
  • When adding more PIDs, the service appears to send a single Mode 01 request with multiple PIDs concatenated (“010C0D…”), which some ELM327/ECU combos don’t accept and answer with “?”.

What is the solution to this problem?