P0672 — Cylinder 2 Glow Plug Circuit

OBD2 code P0672 flags a problem with the diesel glow plug system (cylinder 2 glow plug circuit). The car is usually drivable while you plan the repair. Common culprits: faulty glow plug relay or control module, blown fuse in the glow plug circuit, corroded glow plug connectors.

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 P0672 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 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 P0672 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0672 (parts and labor, USD, independent shop rates): Replace the glow plug relay/module: $150–$450; Replace one glow plug: $80–$200; Replace a full set of glow plugs: $250–$600. Overall, fixing P0672 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

What is the most common cause of P0672?

The most common causes are: faulty glow plug relay or control module, blown fuse in the glow plug circuit, corroded glow plug connectors.

What does OBD2 code P0672 mean?

How much does it cost to fix P0672?

Replace the glow plug relay/module — $150–$450; Replace one glow plug — $80–$200; 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.

Will P0672 clear itself?

Sometimes P0672 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.

Is it safe to drive with P0672?

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.

Diesel engines rely on glow plugs to heat the combustion chambers before and during cold starts, allowing fuel to ignite properly in temperatures where atomization would otherwise fail. Code P0672 triggers when the engine control module detects a fault in the glow plug circuit for cylinder 2 specifically. The PCM monitors voltage and resistance through each cylinder's glow plug circuit during the pre-glow sequence. If the readings fall outside expected parameters — whether due to an open circuit, excessive resistance, or no signal at all — the module logs P0672 and illuminates the check engine light. On inline engines, cylinder 2 is typically the second cylinder counting from the front (the belt end), while V-configuration engines follow manufacturer-specific firing orders that vary by make, so always verify your specific application's cylinder numbering before diving into repairs.

The glow plug system consists of heating elements inside each cylinder, a control relay or module that energizes them on command, and wiring that carries current from the battery through the relay to each plug. When you turn the key on in a diesel, the PCM activates the glow cycle for several seconds depending on ambient temperature, then keeps selected cylinders heated during the initial warm-up phase. This process reduces white smoke, rough running, and hard starts that occur when combustion is incomplete. Because the PCM must confirm the fault persists across multiple ignition cycles under specific conditions before lighting the MIL, a single intermittent reading won't set P0672. The freeze frame data stored alongside the code records engine speed, load, temperature, and vehicle speed at the moment of failure — critical information for replicating the problem during diagnosis.

Symptoms

Check engine light is illuminated on the dashboard
Excessive white or gray smoke from the tailpipe during cold starts
Engine runs rough or misfires until reaching normal operating temperature
Glow plug indicator light remains on after the engine starts
Difficulty starting the engine, especially in cold weather conditions
Reduced power or hesitation under load until the engine warms up

Common Causes

Blown fuse protecting the glow plug circuit
Corrosion or moisture intrusion in the cylinder 2 glow plug electrical connector
Damaged wiring harness or melted connector housing for the cylinder 2 plug
Failed glow plug relay or integrated control module
Internally failed glow plug (burned-out heating element)
Poor ground connection affecting the glow plug circuit
Engine control module software needing an update

How to Diagnose P0672

Connect an OBD2 scanner and confirm P0672 is stored in the PCM. Record all available freeze frame data — this snapshot shows engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault occurred. Replicating these conditions during testing is essential for an accurate diagnosis.
Pull any additional diagnostic trouble codes. Related codes pointing to other cylinders or the relay system often reveal the true root cause. Search manufacturer technical service bulletins using your vehicle identification number on the automaker's website or NHTSA database — many glow plug issues have documented factory fixes or PCM updates.
Perform a thorough visual inspection of the glow plug wiring harness. Look for chafed wires, melted connectors, corrosion buildup, or loose connections at the cylinder 2 glow plug. On some engines, accessing cylinder 2 requires removing the intake manifold or valve cover, which affects labor time and cost.
Measure the resistance of each glow plug with a digital multimeter. A functioning diesel glow plug typically reads between 0.5 and 2 ohms. Infinite resistance or an open circuit indicates a failed plug. Compare readings across all cylinders — if multiple plugs show high resistance, a systemic issue rather than a single component failure may be present.
Check for battery voltage at the glow plug feed wire during the pre-glow cycle. Use a test light or multimeter to verify the relay is delivering power. No voltage indicates a faulty relay or control module; voltage present but the plug shows high resistance confirms a failed glow plug.
After addressing the root cause, clear the code and complete a full drive cycle including the freeze frame conditions. The check engine light should stay off and P0672 should not return. If the code reappears, investigate the control module or wiring harness further.

Repair Options and Costs

If the glow plug relay or control module is at fault, replacement typically runs $150–$450 for parts and labor at an independent shop. A single failed glow plug on cylinder 2 generally costs $80–$200 including labor to remove the old plug and install the replacement. When multiple plugs show degradation or you're addressing pre-emptive maintenance, replacing the complete set of glow plugs — usually four or six depending on your engine — runs $250–$600 for parts and labor combined.

Total Cost to Fix P0672

The final bill hinges entirely on which component triggered the code. Labor rates vary by region and shop, but most P0672 repairs at independent mechanics fall between $80 and $600 total. Always pursue step-by-step diagnosis before purchasing parts — swapping the most expensive component first wastes money when the culprit is simply a corroded connector or blown fuse.

Can You Drive with P0672?

The severity rating for this code is short, meaning immediate shutdown isn't necessary. Once the engine reaches operating temperature, driving characteristics are largely unaffected. The practical concern is cold-weather starting: with cylinder 2's glow plug inoperative, you may experience prolonged cranking, excessive smoke, or a no-start condition on cold mornings. Address this before winter or if you live in a cold climate.