P067A — Cylinder 4 Glow Plug Control Circuit Low

OBD2 code P067A flags a problem with the diesel glow plug system (cylinder 4 glow plug control circuit low). The car is usually drivable while you plan the repair. Common culprits: damaged glow plug wiring or connector, corroded glow plug connectors, burned-out glow plug.

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 P067A 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 Check for supply voltage at the cylinder 4 glow plug control connector first; then measure resistance from the signal wire to ground — near-zero ohms confirms a short to ground in the harness.
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 P067A does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P067A (parts and labor, USD, independent shop rates): Replace one glow plug: $80–$200; Replace the glow plug relay/module: $150–$450; Replace a full set of glow plugs: $250–$600. Overall, fixing P067A 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

Will P067A clear itself?

Sometimes P067A clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose P067A myself?

Start with a scan: confirm P067A, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the cylinder 4 glow plug control, and verify the suspect component against live data before buying parts.

How much does it cost to fix P067A?

Replace one glow plug — $80–$200; Replace the glow plug relay/module — $150–$450; Replace a full set of glow plugs — $250–$600. 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 P067A?

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 P067A?

The most common causes are: damaged glow plug wiring or connector, corroded glow plug connectors, burned-out glow plug.

When your OBD2 scanner pulls a P067A code, the engine control unit has detected that the cylinder 4 glow plug circuit is running at a voltage that's too low — essentially near ground potential. The fault description reads "Cylinder 4 Glow Plug Control Circuit Low," and it falls under the powertrain category since it directly affects engine operation.

Diesel engines rely on glow plugs to warm the combustion chambers during cold starts. Each cylinder has its own plug, and the control module energizes them for a few seconds before and during startup. P067A tells you that cylinder 4's plug isn't receiving the proper voltage or isn't responding correctly to the module's command. On inline engines, cylinder numbering runs from the front (belt end) toward the firewall. On V-configurations, numbering follows the manufacturer's firing order, so consult your service manual if you drive a V6 or V8 diesel. Cylinder accessibility varies significantly between engines — some require removing the intake manifold to reach cylinder 4, which directly impacts labor costs.

The engine control unit monitors the glow plug circuit continuously. When the voltage reading stays outside the acceptable range for enough consecutive drive cycles, the module stores P067A and illuminates the Check Engine light. The stored freeze frame data captures exact operating conditions — engine speed, load, coolant temperature, vehicle speed — when the fault occurred. This snapshot is your best starting point for diagnosis because it tells you what the engine was doing when the control unit noticed the problem.

Common Symptoms of P067A

P067A typically announces itself through cold-start performance problems:

White smoke pouring from the exhaust on cold mornings — unburned fuel passing through a cylinder that can't reach proper combustion temperature
Rough, uneven idle that smooths out once the engine warms up
Check Engine Light illuminated on the dashboard
Glow plug warning light remaining on after the normal pre-heat cycle completes
Difficulty starting the engine, especially when temperatures drop below 40°F
Reduced engine performance under light loads until operating temperature is reached

Common Causes of P067A

The root cause usually falls into one of three categories: wiring problems, failed components, or power supply issues. The most frequent culprits include:

Damaged or chafed wiring insulation causing a short to ground on the cylinder 4 glow plug circuit
Failed cylinder 4 glow plug drawing the signal low or showing infinite resistance
Corroded or moisture-intruded connectors at the glow plug or control module
Blown fuse protecting the glow plug circuit
Faulty glow plug relay or control module unable to supply proper voltage
Missing supply voltage to the glow plug control circuit
Complete burn-out of the cylinder 4 glow plug element

How to Diagnose P067A

Follow this systematic approach to pinpoint the failure without replacing parts unnecessarily:

Connect your OBD2 scanner and confirm P067A is the active code. Record the freeze frame data — note the engine rpm, load percentage, coolant temperature, and vehicle speed at the moment the fault was detected.
Search for any technical service bulletins (TSB) specific to your vehicle make, model, and year. Many manufacturers have published updates or known issues for glow plug problems. Check the manufacturer's website or nhtsa.gov using your VIN.
Visually inspect the wiring harness running to cylinder 4's glow plug. Look for rubbed-through insulation, melted wire jackets from heat proximity, and corrosion at the connector pins. Check both the engine-side connector and the harness connection to the control module.
Measure voltage at the cylinder 4 glow plug connector during the pre-glow cycle using a multimeter. Then check resistance from the signal wire to chassis ground — a reading below 2 ohms indicates a short to ground somewhere in the harness.
Test each glow plug's resistance individually. A healthy diesel glow plug reads 0.5 to 2 ohms. Infinite resistance means an open circuit (burned-out plug), while very low resistance suggests internal damage.
Clear the code and perform a complete drive cycle that reproduces the conditions recorded in the freeze frame. P067A should not return if the fault was repaired. If it comes back immediately, the issue is still present.

Repair Options and Costs

Start with the least expensive fixes and work toward more complex solutions:

Replace single cylinder 4 glow plug: $80–$200
Replace glow plug relay or control module: $150–$450
Replace all glow plugs as a set (recommended if multiple plugs are weak): $250–$600

Labor rates at independent shops typically run $75–$120 per hour. Replacing one glow plug usually takes 30–60 minutes depending on cylinder accessibility. Full set replacement may require 2–4 hours of labor on some engines. Always get a firm quote before work begins, and confirm whether your shop will use OEM or aftermarket glow plugs.

Driving Safety Verdict

Severity level: Short — safe to drive with caution once the engine is warmed up. The primary risk is stranded vehicle failure during cold weather. If cylinder 4's glow plug is completely dead, you'll notice harder starting and increased white smoke whenever temperatures drop. Addressing P067A before cold weather arrives prevents inconvenient no-starts and prevents excess fuel from washing cylinder walls during repeated cold startups. A diesel missing one or more glow plugs will run rough and produce black or white smoke until the combustion chamber reaches operating temperature.