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DTC codes / P06xx · Computer and output circuits / P066E

P066ECylinder 3 Glow Plug Control Circuit Low

P066E means the engine control module (ECM) has detected that the electrical circuit for the cylinder 3 glow plug is drawing less current than expected, which indicates a low-current or open-circuit condition. The ECM monitors glow plug operation during the afterglow phase and sets this code when the measured current falls below the calibrated threshold for that cylinder.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illuminated check engine light, often with no other noticeable symptoms
  • Hard cold starting or extended cranking before the engine fires
  • Rough idle or misfire immediately after a cold start that improves as the engine warms
  • White or blue smoke from the exhaust during cold running
  • Reduced fuel economy during warm-up
  • In severe cold, the engine may fail to start altogether

Common causes, most likely first

  1. Failed cylinder 3 glow plug (open internal element or burned tip)
  2. Damaged or corroded electrical connector at the cylinder 3 glow plug
  3. Chafed, broken, or open-circuit wiring between the glow plug control module and the cylinder 3 glow plug
  4. Faulty glow plug control module not supplying current to cylinder 3
  5. Poor ground connection for the glow plug circuit
  6. ECM software or calibration issue affecting glow plug current monitoring (less common)

How to diagnose and fix it

  1. Scan all modules for stored and pending codes, and record freeze-frame data to confirm the fault is present and not intermittent
  2. Visually inspect the cylinder 3 glow plug, its connector, and the harness for corrosion, looseness, or physical damage
  3. Measure the resistance of the cylinder 3 glow plug with a digital multimeter and compare it to the manufacturer's specification
  4. Check for battery voltage and ground at the glow plug connector during the glow plug pre-heat phase using a multimeter or oscilloscope
  5. Perform a voltage drop test on the power and ground sides of the circuit to identify excessive resistance
  6. If the circuit tests good, substitute a known-good glow plug or control module to isolate the faulty component
  7. Clear the code and verify the repair by running a cold-start glow plug self-test and confirming the code does not return

Glow plug circuit checks that save time

  • A glow plug can pass a simple resistance check when cold yet still draw low current when hot, so always test the circuit during the afterglow phase if the code is intermittent.
  • The glow plug control module often feeds multiple cylinders through a shared power supply; a low-current code on one cylinder can be caused by a poor shared ground rather than the plug itself.
  • Corrosion inside the glow plug connector is a frequent culprit that mimics a failed plug, so inspect and clean the terminals before condemning the plug.
  • This code does not always mean the glow plug is dead; a loose or backed-out plug can cause low current and may also lead to compression leakage if left unchecked.
  • On some vehicles, a weak battery or charging system fault can cause glow plug current to fall below threshold during cranking, setting a low-current code without any glow plug fault.

Can I keep driving with P066E?

You can usually drive the vehicle, but cold starting may be difficult and the engine may run rough until warm; avoid relying on the vehicle for repeated cold starts or in freezing conditions until the fault is repaired.

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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