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DTC codes / P03xx · Ignition system and misfire / P035B

P035BIgnition E Control Signal Circuit Low

P035B is a generic powertrain code that indicates the engine control module (ECM) has detected a low-voltage condition on the ignition coil control circuit for cylinder E, which is typically the fifth cylinder in the engine's firing order. The ECM monitors the control wire that triggers the ignition coil and sets this code when the signal voltage stays below the expected threshold, meaning the coil may not be firing reliably.

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
  • Engine misfire that may feel like a stumble or hesitation during acceleration
  • Rough idle or shaking that worsens when the engine is under load
  • Reduced engine power or a limp-home mode in some vehicles
  • Poor fuel economy due to incomplete combustion in the affected cylinder
  • Occasional backfire or popping sound from the exhaust

Common causes, most likely first

  1. Faulty ignition coil on cylinder E with an internal short or open in its primary winding
  2. Damaged or corroded wiring harness connector at the ignition coil for cylinder E
  3. Chafed, broken, or shorted control wire between the ECM and the ignition coil
  4. Loose or corroded ground connection for the ignition coil circuit
  5. Failed engine control module (ECM) driver circuit for that coil
  6. Aftermarket or incorrect ignition coil that does not meet the original electrical specifications
  7. Oil or coolant contamination in the spark plug well causing a short to ground

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, then clear codes and test-drive to confirm P035B returns
  2. Inspect the ignition coil connector and wiring for corrosion, loose pins, or chafing, and repair as needed
  3. Swap the ignition coil from cylinder E with a known-good coil from another cylinder and see if the misfire and code follow the coil
  4. Measure the resistance of the ignition coil primary and secondary windings and compare with the manufacturer's specification
  5. Use a noid light or oscilloscope to check for a switching signal on the coil control circuit while cranking the engine
  6. Check the ground circuit for the ignition coil with a voltage drop test to ensure it is below 0.1 volts
  7. If the control signal is absent and wiring is intact, diagnose the ECM driver circuit or replace the ECM as a last resort

What the coil control signal really tells you

  • A low control signal does not automatically mean the coil is bad; a shorted coil primary winding can pull the ECM's driver voltage down and set this code even when the coil still fires intermittently.
  • Technicians often overlook a bad ground for the ignition coil circuit, which can mimic a failed ECM driver and cause P035B without any coil fault at all.
  • Swapping coils between cylinders is the fastest way to isolate whether the fault follows the coil or stays with the cylinder, but the code must be cleared and the engine run long enough for the misfire monitor to complete.
  • Aftermarket coils with incorrect resistance values are a common cause of repeat P035B codes on vehicles that have already had coils replaced.
  • P035B is sometimes stored alongside misfire codes for the same cylinder, but the misfire code may not set if the misfire is not severe enough to trigger the monitor.

Can I keep driving with P035B?

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