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DTC codes / P03xx · Ignition system and misfire / P035F

P035FIgnition F Control Signal Circuit High

P035F is a generic powertrain code indicating that the engine control module (ECM) has detected a high-voltage condition on the ignition coil control circuit for the 'F' ignition coil or cylinder. The ECM commands the coil to fire by pulling the control wire low, but the voltage on that circuit remains higher than expected, so the ECM flags the circuit as faulty.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Rough idle or misfire that may be intermittent
  • Engine hesitation or stumble during acceleration
  • Reduced fuel economy due to incomplete combustion
  • In some cases, the engine may enter limp mode or shut down a cylinder

Common causes, most likely first

  1. Open or high-resistance in the ignition coil control wire between the ECM and coil
  2. Faulty ignition coil with an open internal primary winding
  3. Corroded, loose, or damaged connector pins at the coil or ECM
  4. Damaged or chafed wiring harness causing an open circuit
  5. Failed ECM driver for that ignition coil control circuit
  6. Aftermarket or incorrect ignition coil with wrong resistance
  7. Poor ground connection for the ignition coil

How to diagnose and fix it

  1. Inspect the ignition coil connector and wiring for obvious damage, corrosion, or loose pins
  2. Measure resistance of the ignition coil primary circuit and compare to specification
  3. Check for continuity and voltage drop on the control wire from the ECM to the coil
  4. Swap the suspect ignition coil with a known-good coil from another cylinder to see if the code follows
  5. Test the control circuit with a noid light or oscilloscope to verify the ECM is commanding the coil
  6. Repair any open or high-resistance wiring, connectors, or grounds
  7. If all circuits test good, replace the ignition coil; if the code persists, diagnose the ECM

What the high side of the coil circuit really means

  • A high-voltage reading on the control circuit often indicates an open circuit rather than a short, because the ECM's internal pull-up resistor keeps the voltage high when the coil is disconnected.
  • The 'F' coil designation does not always correspond to cylinder 6; always consult the specific vehicle's coil identification chart to avoid replacing the wrong coil.
  • A faulty ignition coil can cause a high control signal code without setting a misfire code, so do not assume the coil is good just because no P030x codes are present.
  • Corroded terminals inside the coil boot or connector are a frequent cause that visual inspection alone may miss; wiggle testing while monitoring the circuit can reveal intermittent opens.
  • After replacing a coil, always clear the codes and perform a road test with live data to confirm the control circuit voltage switches correctly under load.

Can I keep driving with P035F?

You can usually drive the vehicle short distances to a repair shop, but avoid heavy acceleration or towing because a misfire can overheat the catalytic converter. If the engine is running very rough or flashing the check engine light, stop driving and have it towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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