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Ignition B Control Signal Circuit High

Jump to the fix

Severity

High

Can I keep driving?

Avoid extended driving; visit a service soon.

First step

Identify the cylinders involved from the misfire counters and the freeze frame data

  • PPowertrain
  • 0Generic code
  • 3Ignition / Misfire
  • 0FSequence number

What does it mean?

To trigger the coil on the ignition B channel the module has to pull the control line low from its rest voltage. P030F is set when the module commands the channel but the measured voltage stays high, so the current it expects never flows. That points to an open or high resistance connection in the control path, or to battery voltage arriving on the line from another circuit. Either way the coil is not triggered correctly, so the cylinders it serves either misfire or do not fire at all, and the misfire monitor usually reports them at the same time.

Symptoms

  • Persistent misfire, engine shake at idle and a flat feeling under acceleration
  • MIL on and flashing when the misfire is heavy
  • Hard starting, worse when the engine is cold or the weather is damp
  • Popping or backfiring from the exhaust and a raw fuel smell
  • Poor fuel economy
  • Reduced power and, on some vehicles, limp mode

Likely causes

  • High resistance joint, corroded terminal or a partial break in the control wire
  • Control line shorted to battery voltage through damaged insulation or an incorrect repair
  • Spread or backed-out terminals reducing contact pressure in the coil or module connector
  • Open igniter input inside the coil or the ignition module
  • Poor ground at the ignition module, so the driver cannot pull the line down
  • Failed module output stage, evaluated only after the wiring has been proven good

How to fix it

  1. Identify the cylinders involved from the misfire counters and the freeze frame data
  2. Probe the coil and module connectors for terminal tension and corrosion, and clean or renew terminals as needed
  3. Measure the control line voltage with the ignition on and while cranking; a line that never pulls down confirms the condition
  4. Carry out continuity and voltage drop tests along the control wire from the module pin to the coil pin
  5. Check the ignition module supply, ground and the relevant fuse
  6. Test for a short to a live circuit by measuring the line with the module disconnected
  7. Repair the wiring or renew the coil or module as the results dictate, then clear the code and road test

Codes From the Same System

All Fault Codes

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.