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DTC codes / P06xx · Computer and output circuits / P067B

P067BCylinder 4 Glow Plug Control Circuit High

P067B means the engine computer has detected an abnormally high voltage on the control circuit for the number 4 cylinder glow plug, which usually points to an open circuit or a failed glow plug rather than a short to ground. The computer commands the glow plug on and monitors the circuit; when the voltage stays higher than expected, it flags this code and may disable glow plug operation for that cylinder.

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

Symptoms you may notice

  • Illuminated check engine light or glow plug warning lamp, often with no other symptoms
  • Hard cold starting or extended cranking before the engine fires
  • Rough idle and white smoke from the exhaust immediately after a cold start
  • Misfire or hesitation during the first few minutes of engine operation
  • Increased fuel consumption during warm-up
  • In some vehicles, a reduced-power or limp mode message on the dash

Common causes, most likely first

  1. Failed number 4 glow plug with an open internal element
  2. Damaged or disconnected glow plug electrical connector at the cylinder
  3. Broken or chafed wire in the glow plug control circuit between the module and the plug
  4. Faulty glow plug control module output for that cylinder
  5. Corroded or loose ground connection shared by the glow plug circuit
  6. Engine control module (ECM) driver fault, though this is less common

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm the code is current and not history
  2. Inspect the number 4 glow plug connector and wiring for looseness, corrosion, or chafing
  3. Measure glow plug resistance with a digital multimeter and compare it to the manufacturer's specification
  4. Check for battery voltage at the glow plug connector with the key on and the engine cold, using a helper to command the glow plugs on
  5. Perform a voltage drop test on the ground side of the glow plug circuit to rule out a bad ground
  6. If voltage is present but the plug does not heat, replace the glow plug and clear the code
  7. If the circuit tests good but the code returns, test or substitute the glow plug control module before condemning the ECM

What a high glow plug circuit really means

  • A high-voltage code on a glow plug circuit almost always means the circuit is open, so the computer sees full command voltage with no current flow, not that the plug is shorted.
  • Many technicians replace the glow plug first and then find a corroded connector pin or a broken wire two inches up the harness, so always inspect the connector before condemning the plug.
  • On some vehicles the glow plug control module is integrated into the engine control module, and a single failed output can set this code even though the plug itself is fine.
  • A weak battery or a poor engine ground can cause the glow plug module to log a high-circuit code because the module's internal switching reference is disturbed during the cold-start current surge.
  • This code does not always mean the glow plug has failed completely; a plug with high resistance from carbon buildup can trigger it intermittently before it fails outright.

Can I keep driving with P067B?

You can usually drive the vehicle, but cold starting will be harder and the engine may run rough and smoke until it warms up. Avoid long cranking periods and have the circuit checked soon, especially if you live in a cold climate where the glow plugs are needed for reliable starting.

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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