P0680 – Cylinder 10 Glow Plug Circuit

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit | Location: Cylinder 10

Definition source: SAE J2012/J2012DA (industry standard)

P0680 indicates a fault detected in the cylinder 10 glow plug circuit. In diesel applications, glow plugs are electric heaters used to improve cold-start combustion quality. When the control module commands glow plug operation, it expects the cylinder 10 circuit to respond electrically within an acceptable pattern. If the module detects an abnormal circuit condition (such as an open, short, or excessive resistance) on the cylinder 10 glow plug path, it can set P0680 and may illuminate the malfunction indicator. Diagnostic behavior, test strategy, and the exact circuit layout vary by vehicle, so always confirm connector locations, pin IDs, and test specifications using the appropriate service information.

What Does P0680 Mean?

P0680 means the powertrain control system has identified a problem in the Cylinder 10 Glow Plug Circuit. The code points to the electrical circuit associated with the glow plug for cylinder 10, not to fuel quality, compression, or a confirmed failed glow plug by default. The module monitors the commanded operation of the glow plug system and evaluates the electrical response it sees from the cylinder 10 circuit. If that monitored response indicates a circuit fault, P0680 is stored. The specific monitor logic and whether the vehicle uses individual glow plug drivers or a shared control device varies by platform, so the code should be diagnosed with circuit testing rather than assumptions.

Quick Reference

  • Subsystem: Cylinder 10 glow plug electrical circuit (glow plug, harness, connectors, and any associated control/driver path).
  • Common triggers: Open circuit, short to ground or power, high resistance, poor terminal contact, or a control/driver output that does not match the command.
  • Likely root-cause buckets: Wiring/connector issues; glow plug fault; power/ground feed problems; control module/driver concerns (varies by vehicle).
  • Severity: Usually most noticeable during cold starts; may cause hard starting, rough running after start, increased smoke, or extended cranking.
  • First checks: Visual inspection of cylinder 10 harness/connectors, verify power/ground integrity, check for corrosion/heat damage, and confirm cylinder identification.
  • Common mistakes: Replacing the glow plug without testing the circuit, misidentifying cylinder 10, ignoring shared power/ground issues, or skipping connector pin-fit checks.

Theory of Operation

The glow plug system heats the combustion chamber area to support ignition when engine and intake temperatures are low. A control module or dedicated driver commands glow plug operation based on temperature inputs and operating conditions. Depending on design, each glow plug may be individually driven or supplied through a common feed with separate control paths. The cylinder 10 glow plug circuit includes the glow plug element, its connector, wiring, and the control/driver path that delivers and controls current.

To determine whether the circuit is operating correctly, the module compares its command to the electrical feedback it can infer or measure (varies by vehicle). Abnormal conditions such as an open circuit, a short, or excessive resistance can prevent the expected electrical response, triggering P0680. Because the monitoring method differs by platform, accurate diagnosis relies on checking the circuit end-to-end using the correct wiring diagram and service procedures.

Symptoms

  • Hard start during cold ambient conditions or after an overnight soak.
  • Extended cranking before the engine starts, especially when cold.
  • Rough idle or misfire-like shaking shortly after startup that improves as the engine warms.
  • White/gray smoke on cold start due to incomplete combustion.
  • Reduced performance briefly after startup until combustion stabilizes.
  • Warning lamp illuminated (malfunction indicator), sometimes accompanied by a glow system indicator depending on the vehicle.

Common Causes

  • Open circuit or high resistance in the Cylinder 10 glow plug feed wire between the control module/relay and the glow plug
  • Poor connection at the Cylinder 10 glow plug connector (loose fit, corrosion, fretting, bent or backed-out terminal)
  • Open or high resistance in the Cylinder 10 glow plug ground path (varies by vehicle design)
  • Glow plug internal fault causing abnormal circuit behavior under load (verify with testing, not assumption)
  • Damage to the engine harness near heat sources or abrasion points affecting the Cylinder 10 glow plug circuit
  • Glow plug control module/driver channel fault for Cylinder 10 (if individually driven)
  • Glow plug relay or power distribution issue that affects the monitored output to Cylinder 10 (architecture varies by vehicle)
  • Power or ground supply problem to the glow plug control module (shared supply/ground creating false circuit faults)

Diagnosis Steps

Tools that help: a scan tool capable of reading freeze-frame and data parameters related to glow plug command/status, a digital multimeter, and backprobing tools. A wiring diagram and connector views from service information are strongly recommended because cylinder numbering, control architecture, and test points vary by vehicle. If available, use a test light or an approved load tool to confirm circuit integrity under load.

  1. Confirm the code and capture data: Scan for DTCs and record freeze-frame data. Note any related glow plug, control module power/ground, or communication codes. Clear codes only after saving data.
  2. Verify cylinder identification: Use service information to confirm Cylinder 10 location and cylinder numbering. Identify the exact glow plug, its connector, and the harness routing for that cylinder’s circuit.
  3. Run a controlled repeat test: With the scan tool, command the glow plug system on (if bi-directional control is supported and conditions allow). Observe any available parameters for glow plug command and circuit feedback. If bi-directional control is not available, repeat a cold-start cycle and log data.
  4. Perform a visual inspection (focused): Inspect the Cylinder 10 glow plug connector for poor fit, corrosion, oil intrusion, heat damage, or pulled wires. Follow the harness back to the main loom and to the control module/relay area looking for chafing, pinched sections, or previous repair points.
  5. Connector integrity checks: With the connector disconnected, inspect terminals for tension and alignment. Look for spread terminals, bent pins, or evidence of arcing. Repair terminal issues using correct service procedures rather than forcing terminals to fit.
  6. Check for opens and high resistance (power side): Using the wiring diagram, test continuity of the Cylinder 10 glow plug feed circuit end-to-end (module/relay to glow plug connector). If continuity is poor, isolate the open by testing segment-by-segment at intermediate connectors.
  7. Check ground path integrity (as applicable): If the glow plug uses a dedicated ground wire, test continuity and resistance of the ground circuit to its ground point. If the glow plug grounds through its body/engine, inspect for installation/seat issues and verify the engine ground paths are intact (vehicle design varies).
  8. Load test the circuit (important): If safe and supported by service procedures, verify the circuit can carry current by testing under load. A circuit may show continuity with a meter yet fail under load due to corrosion, partial breaks, or poor terminal contact.
  9. Voltage-drop testing while commanded on: With the glow plug commanded on, perform voltage-drop tests across the feed side connections (module/relay output to glow plug terminal) and across the ground return path (glow plug ground to battery/ground reference as applicable). Excessive drop indicates unwanted resistance; pinpoint the exact connection by moving the meter leads closer to each connector or splice.
  10. Wiggle test for intermittents: While monitoring scan tool data and/or meter readings, gently wiggle the Cylinder 10 harness, connector, and nearby junctions. If the fault appears or readings change, locate the sensitive area and inspect for broken strands, poor crimp, or pin fit problems.
  11. Isolate the component vs. driver: If wiring and connections test good, evaluate the glow plug itself per service information (including any specified resistance/functional checks). If the component tests good, focus on the control module/driver output for Cylinder 10 and its power/ground supplies, since a weak driver or supply issue can mimic a circuit fault.
  12. Verify repair: After repairs, clear DTCs and repeat the same enable conditions that originally set the code (often cold-start related). Use live-data logging to confirm stable command/feedback and recheck for pending codes after a complete drive cycle.

Professional tip: Prioritize finding unwanted resistance at terminals and splices over replacing parts. Glow plug circuits are high-current by nature, so small amounts of corrosion or poor pin tension can pass basic continuity checks yet fail under load. Use voltage-drop testing during an active command, and move your test points one connection at a time to quickly pinpoint the exact location of the resistance.

Need wiring diagrams and factory-style repair steps?

Powertrain faults often require exact wiring diagrams, connector pinouts, and guided test steps. A repair manual can help you confirm the cause before replacing parts.

Factory repair manual access for P0680

Check repair manual access

Possible Fixes & Repair Costs

Repair costs for P0680 vary widely because the fault is circuit-related and the correct fix depends on test results, access to the cylinder 10 glow plug and harness routing, and whether the issue is wiring, the glow plug itself, or the control side. Labor time can also vary by vehicle design.

  • Repair or replace damaged wiring in the cylinder 10 glow plug circuit (chafing, melted insulation, broken conductor)
  • Clean, tighten, or replace affected connectors/terminals (corrosion, spread pins, poor pin fit, water intrusion)
  • Replace the cylinder 10 glow plug only after confirming it fails resistance/continuity testing per service information
  • Repair power feed or ground paths associated with the glow plug control circuit after verifying with voltage-drop testing
  • Service or replace the glow plug control module/driver only after verifying the circuit and glow plug are good and command/control is abnormal
  • Correct installation issues (improper routing, connector not fully seated, terminal backing out) and secure the harness to prevent repeat faults

Can I Still Drive With P0680?

You can often drive with P0680, but expect harder starting, longer cranking, rough idle after start, and increased smoke during cold starts because glow plug assistance may be reduced for cylinder 10. If you have a no-start condition, severe misfire, reduced power warnings, or any safety-related warnings, do not continue driving—diagnose and repair first. In cold conditions, the risk of a start failure increases, so address the circuit fault promptly and verify proper operation after repairs.

What Happens If You Ignore P0680?

Ignoring P0680 can lead to progressively worse cold-start performance, extended cranking, rough running until warm, and increased exhaust smoke during startup. Continued operation with an unresolved circuit fault may also contribute to additional diagnostic trouble codes related to glow plug control, cylinder contribution, or starting performance, and it can complicate troubleshooting later by adding intermittent wiring symptoms.

Compare nearby cylinder glow trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0682 – Cylinder 12 Glow Plug Circuit
  • P0681 – Cylinder 11 Glow Plug Circuit
  • P0679 – Cylinder 9 Glow Plug Circuit
  • P0678 – Cylinder 8 Glow Plug Circuit
  • P0677 – Cylinder 7 Glow Plug Circuit
  • P0676 – Cylinder 6 Glow Plug Circuit

Key Takeaways

  • P0680 indicates a problem in the cylinder 10 glow plug circuit, not a confirmed mechanical engine issue.
  • Most fixes are found through circuit checks: connectors, wiring integrity, power/ground quality, and verified component tests.
  • Replace parts only after confirming the fault with continuity, resistance, and voltage-drop testing per service information.
  • Cold-start drivability is the most common impact; severity increases in low temperatures.
  • Post-repair verification should include a re-scan, commanded operation check (if supported), and a road test/cold-start check when feasible.

Vehicles Commonly Affected by P0680

  • Diesel-equipped vehicles that use individual cylinder glow plugs
  • Engines with a cylinder 10 configuration (layout and numbering vary by vehicle)
  • Vehicles operating in cold climates where glow plug demand is high
  • High-mileage vehicles with heat-cycled engine wiring harnesses
  • Vehicles with prior engine work where harness routing or connectors may have been disturbed
  • Applications with externally mounted glow plug control modules and long harness runs
  • Vehicles exposed to corrosion-prone environments that affect connectors and grounds
  • Vehicles with frequent short-trip usage that increases start cycles and electrical loading

FAQ

Does P0680 mean the cylinder 10 glow plug is bad?

No. P0680 indicates a cylinder 10 glow plug circuit fault. The glow plug could be faulty, but so could the wiring, connector terminals, power/ground paths, or the control driver. Confirm with circuit tests before replacing parts.

Can a wiring problem cause P0680 even if the glow plug tests good?

Yes. A glow plug can pass a basic resistance check while the circuit still fails due to high resistance at a connector, corrosion, poor pin fit, damaged insulation, or a weak ground. Voltage-drop testing under load is commonly needed to find these issues.

Will P0680 always cause a check engine light?

Many vehicles will illuminate a malfunction indicator when the fault is detected, but indicator behavior varies by vehicle and how the monitor is classified. Some platforms may store the code as pending first or show a separate preheat/glow indicator instead. Always verify with a scan tool.

Why is the problem worse on cold mornings?

Glow plugs are most important during cold starts. If the cylinder 10 glow plug circuit is not functioning correctly, that cylinder may not receive proper preheating, leading to harder starting and rougher running until combustion stabilizes. The difference may be minimal when the engine is already warm.

After repairs, what should be verified to ensure P0680 is fixed?

Confirm the repair by clearing codes, running the applicable monitor if supported, and verifying commanded glow operation and circuit integrity with appropriate tests. If possible, perform a cold-start verification and review scan data for any returning pending codes or related glow plug circuit faults.

For the most reliable result, base the final repair decision on measured circuit integrity and verified component tests for the cylinder 10 glow plug circuit, using the correct service information for your specific vehicle configuration.