P0680 — Cylinder 10 Glow Plug Circuit

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 P0680 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 P0680 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0680 (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 P0680 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 are the symptoms of P0680?

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

What does OBD2 code P0680 mean?

Cylinder 10 Glow Plug Circuit (P0680): a powertrain (engine/transmission) fault affecting the diesel glow plug system. The car is usually drivable while you plan the repair. Most often caused by faulty glow plug relay or control module, blown fuse in the glow plug circuit, damaged glow plug wiring or connector.

How much does it cost to fix P0680?

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.

What is the most common cause of P0680?

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

Will P0680 clear itself?

Sometimes P0680 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.

The engine control unit continuously monitors all electrical components and sensors, comparing live readings against factory-calibrated parameters. When those readings fall outside acceptable ranges for the cylinder 10 glow plug circuit, the ECU stores trouble code P0680. This particular code applies specifically to cylinder 10 — on inline engines, cylinders are numbered from the front pulley end, while V-type engines follow manufacturer-specific firing order diagrams that vary by brand. Cylinder numbering matters for repairs because some cylinder positions require additional disassembly, such as removing the intake manifold to access the glow plug, which increases labor time significantly.

Diesel glow plugs are resistance-heating elements that warm the combustion chamber before and during starting, allowing fuel to ignite reliably in cold conditions. The ECU activates the glow plug circuit for several seconds before cranking, then monitors voltage and current flow to confirm proper operation. When the feedback signal does not match expected values, P0680 is set. Along with the trouble code, the control module records a freeze frame — a snapshot of engine RPM, load, coolant temperature, and vehicle speed at the exact moment the fault occurred. This snapshot is one of the most useful diagnostic tools because it reveals the operating conditions present when the failure was detected.

Common Symptoms of P0680

White smoke billowing from the exhaust after a cold start, caused by unburned fuel passing through a cylinder that cannot reach proper combustion temperature
The glow plug warning light remaining illuminated on the instrument cluster after the engine starts
Rough, uneven idle that smooths out once the engine reaches normal operating temperature
The Check Engine Light illuminated on the dashboard
Difficulty starting the engine, especially during cold weather when glow plugs work hardest

What Causes P0680?

Damaged or worn wiring harness feeding the cylinder 10 glow plug, including insulation breakdown, broken strands, or loose connectors
A blown fuse in the glow plug control circuit, which interrupts power delivery to the heating element
A burned-out glow plug filament that no longer produces heat due to age, corrosion, or manufacturing defect
A failed glow plug relay or engine control module that cannot properly activate the heating circuit

How to Diagnose P0680

Connect an OBD2 scanner to the vehicle diagnostic port, verify that P0680 is stored in the ECU memory, and record the freeze frame data for reference during the repair process.
Check for any additional diagnostic trouble codes that may be stored alongside P0680 — related codes often point to the underlying cause, such as a power supply issue or controller failure.
Consult manufacturer technical service bulletins for your specific make and model — many P0xxx codes have documented factory fixes, software updates, or known issues that can shorten diagnosis time.
Perform a thorough visual inspection of the glow plug wiring harness and electrical connectors for cylinder 10, looking for damaged insulation, corrosion, chafing from contact with hot components, or loose fitting connections.
Measure the resistance of the cylinder 10 glow plug using a digital multimeter — an open circuit reading indicates a failed plug that requires replacement.
Verify voltage presence at the glow plug bus bar during the pre-glow cycle using a multimeter or test light to confirm the control circuit is delivering power.

Repair Options and Costs

The appropriate repair depends entirely on which component actually failed, so diagnosis should precede any parts purchasing. The glow plug relay or control module can fail over time due to heat cycling and electrical stress; replacement typically costs $150–$450 including parts and labor. When only a single glow plug has burned out, the repair is straightforward — one replacement glow plug with labor runs $80–$200. Many technicians recommend replacing all glow plugs at once on high-mileage diesel engines since they age at similar rates, and a full set replacement including labor costs $250–$600.

Total Cost to Fix P0680

Most P0680 repairs fall between $80 and $600 depending on the root cause. Replacing one failed glow plug sits at the lower end of that range, while swapping the control module or completing a full set replacement costs more. The most expensive scenario is rarely the most likely — always complete proper diagnosis before purchasing components, because swapping expensive parts on speculation rarely ends well for your wallet.

Can You Drive with P0680?

Once the engine is running and warmed up, driving with P0680 stored poses minimal immediate risk. The real concern is cold-weather starting: if multiple glow plugs have failed, the engine may refuse to crank on a frosty morning. Address this code before cold season arrives, especially if your vehicle relies on traditional glow plug starting rather than grid heaters or advanced cold-start systems.