P0682 — Cylinder 12 Glow Plug Circuit

OBD2 code P0682 flags a problem with the diesel glow plug system (cylinder 12 glow plug circuit). The car is usually drivable while you plan the repair. Common culprits: blown fuse in the glow plug circuit, faulty glow plug relay or control module, 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 P0682 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 P0682 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for P0682 (parts and labor, USD, independent shop rates): Replace a full set of glow plugs: $250–$600; Replace one glow plug: $80–$200; Replace the glow plug relay/module: $150–$450. Overall, fixing P0682 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 do I diagnose P0682 myself?

Start with a scan: confirm P0682, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the diesel glow plug system, and verify the suspect component against live data before buying parts.

How much does it cost to fix P0682?

Replace a full set of glow plugs — $250–$600; Replace one glow plug — $80–$200; 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.

What are the symptoms of P0682?

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

Is it safe to drive with P0682?

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.

Will P0682 clear itself?

Sometimes P0682 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.

Diesel engines rely on glow plugs to warm the combustion chambers during cold starts. Unlike spark plugs found in gasoline engines, glow plugs are heating elements that raise cylinder temperature so diesel fuel can ignite properly in sub-optimal conditions. When the engine control unit detects a problem with cylinder 12's glow plug circuit, it logs trouble code P0682.

This code falls within the powertrain category of OBD2 diagnostics, meaning it relates directly to engine and transmission operation. Cylinder 12 is typically found on the rear bank of V-configuration diesel engines. On inline-six or inline-four diesel engines, cylinder 12 would not exist—these engines max out at six or four cylinders respectively. The PCM logs P0682 only after confirming the fault across multiple drive cycles, not from a single anomalous reading. The freeze frame data stored alongside P0682 is particularly valuable: it captures engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault triggered, giving you precise conditions to replicate during testing.

Symptoms of P0682

When P0682 is active, you may notice one or more of the following:

Persistent check engine light on the dashboard
Engine runs rough during the warm-up period
White smoke billowing from the exhaust on cold mornings
Glow plug indicator remaining illuminated after the engine starts
Difficulty starting the engine, especially in colder temperatures

Common Causes

The root cause of P0682 typically traces back to one of these issues:

A failed glow plug relay or control module unable to energize cylinder 12
Corrosion or moisture intrusion at the cylinder 12 glow plug electrical connector
A blown fuse protecting the glow plug circuit
Damaged wiring, melted insulation, or loose connector terminals in the affected circuit
The glow plug itself has burned out internally
An open circuit between the PCM and the glow plug

How to Diagnose P0682

Follow these steps to isolate the fault accurately:

Connect a diagnostic scanner and verify P0682 is stored. Record the freeze frame data—these parameters tell you engine temperature, load, and speed when the failure occurred.
Scan for any additional diagnostic trouble codes. Secondary codes often point to the underlying problem. Consult manufacturer technical service bulletins using your VIN, as many glow plug issues have known fixes or updated calibrations.
Perform a thorough visual inspection of the wiring harness serving the glow plug system. Look for damaged insulation, evidence of heat damage, corrosion buildup, and ensure all connectors are fully seated with intact locking tabs.
Test each glow plug individually using a multimeter. A healthy glow plug reads between 0.5 and 2 ohms of resistance; an open circuit indicates a failed unit.
Verify voltage present at the glow plug bus bar during the pre-glow cycle using a digital multimeter. No voltage suggests a relay failure or blown fuse upstream.
After addressing the suspected cause, clear the code and perform a complete drive cycle—including cold-start conditions matching your freeze frame data—to confirm the repair holds.

Repair Options and Costs

Resolution depends entirely on which component triggered P0682:

Replace a single faulty glow plug: parts and labor typically run $80–$200
Replace the glow plug relay or control module: parts and labor generally cost $150–$450
Replace the entire glow plug set as a preventive measure: parts and labor typically total $250–$600

Total Repair Cost

For most vehicles experiencing P0682, expect to pay between $80 and $600 depending on which part failed. Labor rates vary by region and shop, but independent shops typically charge $75–$120 per hour. Diagnosing the actual cause before purchasing parts is strongly recommended—jumping to the most expensive repair scenario first wastes money when the problem is often a simple fuse or corroded connector.

Can You Drive With P0682?

Once the engine reaches operating temperature, the vehicle is generally safe to drive. The critical concern is cold-start capability: with cylinder 12 unable to heat properly, you may experience hard starting or complete failure to start on cold mornings. If you live in a cold climate, prioritize this repair before winter arrives.