P067B — Cylinder 4 Glow Plug Control Circuit High

OBD2 code P067B flags a problem with the diesel glow plug system (cylinder 4 glow plug control circuit high). The car is usually drivable while you plan the repair. Common culprits: corroded glow plug connectors, faulty glow plug relay or control module, damaged glow plug wiring or connector.

powertrain (engine/transmission)

Is it safe to drive?

Short-term driving is OK Safe to drive once the engine is started and warmed up. The main risk is cold-weather starting: with several dead plugs the engine may not start on a cold morning. Fix before winter.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm P067B is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many P0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the diesel glow plug system for damage, corrosion, chafing or poor contact.
Subsystem check With the cylinder 4 glow plug control disconnected, measure signal voltage at the harness connector: a high reading with the component unplugged indicates a short to power in the harness; if it drops to normal, the component itself is faulty.
Subsystem check Measure resistance of each glow plug — an open plug reads infinite resistance.
Subsystem check Check voltage at the glow plug rail during the pre-glow phase.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm P067B does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P067B (parts and labor, USD, independent shop rates): Replace one glow plug: $80–$200; Replace a full set of glow plugs: $250–$600; Replace the glow plug relay/module: $150–$450. Overall, fixing P067B usually costs between $80 and $600. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How much does it cost to fix P067B?

Replace one glow plug — $80–$200; Replace a full set of glow plugs — $250–$600; Replace the glow plug relay/module — $150–$450. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Is it safe to drive with P067B?

Safe to drive once the engine is started and warmed up. The main risk is cold-weather starting: with several dead plugs the engine may not start on a cold morning. Fix before winter.

What is the most common cause of P067B?

The most common causes are: corroded glow plug connectors, faulty glow plug relay or control module, damaged glow plug wiring or connector.

What are the symptoms of P067B?

Drivers most often notice: white smoke after a cold start, Check Engine Light on, glow plug warning light staying on, rough idle until warmed up.

What does OBD2 code P067B mean?

Diesel engines rely on glow plugs to ignite the air-fuel mixture during cold starts. When the engine control module detects that the voltage on cylinder 4's glow plug control circuit exceeds normal limits, it logs OBD2 code P067B. This specific fault code tells you the problem is isolated to cylinder 4, which helps narrow down the search considerably.

On most inline diesel engines, cylinder numbering starts at the front of the block (the end with the accessory belt). V-configuration engines vary by manufacturer, so consulting your owner's manual or service documentation for the correct firing order eliminates guesswork. The phrase "circuit high" in the code description means the PCM sees something close to full battery voltage on a circuit that should be switching on and off under load. That points toward a short to a power source, a broken ground path, or a component that has failed in a way that forces the signal high.

The engine control module sets P067B after comparing live sensor data against factory-calibrated thresholds, typically across multiple drive cycles. When the code is stored, the PCM also captures a freeze frame snapshot—engine speed, load percentage, coolant temperature, and vehicle speed at the moment of failure. That data is invaluable for reproducing the fault condition during testing.

Common Symptoms of P067B

P067B most often shows up as a combination of cold-start problems and warning lights. Watch for these signs:

Persistent white exhaust smoke, especially during cold mornings
Illuminated Check Engine light on the dashboard
Glow plug indicator that fails to turn off after startup
Rough, uneven idle that smooths out once the engine reaches operating temperature
Difficulty starting the vehicle in cold weather conditions
Noticeable performance decline or reduced fuel economy in severe cases

What Causes P067B?

Several different failures can trigger the same P067B code. The most probable culprits, listed from most to least common:

Cylinder 4 glow plug itself has failed internally, pulling the control circuit high
The signal wire to cylinder 4 is shorted directly to battery positive voltage
Broken or corroded ground return path for the cylinder 4 glow plug control circuit
Malfunctioning glow plug relay or integrated control module
Blown fuse protecting the glow plug heating circuit
Physically burned-out or damaged glow plug filament
Wiring harness damage or loose/damaged electrical connector at the glow plug

How to Diagnose P067B

Follow this systematic approach to pinpoint the root cause without replacing parts unnecessarily.

Connect a quality OBD2 scanner and verify that P067B is the active code. Record the freeze frame data—recreating those exact engine conditions makes diagnosis far more reliable.
Scan for any additional trouble codes. Related electrical faults often reveal the true origin. Check manufacturer TSB databases using your VIN to see if a known defect or software update applies.
Perform a visual inspection of all wiring and connectors in the glow plug circuit. Look for damaged insulation, corrosion buildup, broken wires, or connectors that are not fully seated.
Disconnect the cylinder 4 glow plug harness and check voltage at the loose connector. If battery-level voltage appears with the component unplugged, the harness itself has a short to power. If the voltage drops to normal range, the glow plug or its internal control is the problem.
Measure individual glow plug resistance with a multimeter. A properly functioning plug shows a resistance reading between 0.5 and 2 ohms—anything reading infinite or out of range indicates failure.
With everything reconnected, verify proper voltage delivery to the glow plug rail during the pre-glow sequence using a DVOM or oscilloscope.
Clear the code, complete a full drive cycle matching the freeze frame conditions, and confirm that P067B does not return.

Repair Options for P067B

Once diagnosis identifies the exact faulty component, the fix becomes straightforward. Replace only the failed part first:

Replace single glow plug (cylinder 4): $80–$200
Replace complete glow plug set (all cylinders): $250–$600
Replace glow plug control relay or module: $150–$450

Always address the cheapest likely causes before investing in more expensive components.

How Much Does It Cost to Fix P067B?

Actual repair costs depend entirely on which part failed and whether you tackle the work yourself or pay a shop. Parts and labor estimates at independent shops (USD):

Single cylinder 4 glow plug replacement: $80–$200
Full set of four or six glow plugs: $250–$600
Glow plug relay or integrated control module: $150–$450

Most P067B repairs fall in the $80 to $600 range. Spending time on accurate diagnosis before purchasing parts prevents the most expensive repair from becoming the default assumption.

Can You Drive with P067B?

Severity level: short. Once the engine warms up, driving poses no immediate safety concern. However, a faulty glow plug on cylinder 4 means cold starts will suffer—hard cranking, white smoke, and possible no-start conditions in freezing temperatures. Address this before cold weather arrives.