P0680 — Cylinder 10 Glow Plug Circuit/Open #

Note: The wording of this diagnostic trouble code (DTC) may differ depending on the vehicle manufacturer. Always refer to your OEM (Original Equipment Manufacturer) documentation for confirmation.

• Cylinder 10 Glow Plug Circuit/Open (Generic/Multiple OEMs)
• Glow Plug Circuit Open, Cylinder 10 (Ford, GM, Mercedes-Benz)
• Cylinder 10 Glow Plug Control Circuit Malfunction (Cummins/Chrysler/RAM Trucks)
• Glow Plug Open Circuit, Cylinder 10 (Isuzu, Iveco)

Summary of Code P0680 #

P0680 is an OBD-II diagnostic trouble code that indicates a problem with the glow plug circuit for cylinder 10. Glow plugs are electrically heated elements used to aid cold starting in diesel engines by warming the combustion chamber. When the Powertrain Control Module (PCM) or Engine Control Module (ECM) detects that the current or resistance in the glow plug circuit for cylinder 10 is outside of normal parameters—typically due to an open circuit—it triggers this code. This can result in extended cranking, rough running, or increased emissions, especially during cold starts. While the DTC itself points to cylinder 10, the root cause may involve wiring, connectors, the glow plug relay, or the glow plug itself.

Common Symptoms for Code P0680 #

When P0680 is present, the most noticeable effects often happen during cold starts or in low ambient temperatures. The engine may struggle to ignite smoothly, and you might notice some operational roughness. Sometimes, there are no immediate drivability issues, but the Check Engine Light will always illuminate. Over time, persistent starting difficulties can lead to battery drain or excessive fuel in the exhaust, which may damage other emission components.

• Hard starting or extended cranking, especially in cold weather
• Rough idle after startup
• Increased white smoke from the exhaust during cold start
• Check Engine Light (CEL) illuminated
• Possible reduced fuel economy if starting problems persist
• Occasionally, misfire or hesitation until engine warms up

Probable Causes of Code P0680 (Most to Least Common) #

While the code specifically references cylinder 10, the actual fault can originate from several points within the glow plug circuit. The most frequent culprit is a failed or worn-out glow plug, but wiring issues and control module faults are also possible. Diagnosing P0680 requires a methodical approach, as multiple components must function correctly for proper glow plug operation.

1. Defective glow plug (cylinder 10) — open circuit or excessive resistance
2. Faulty wiring or connectors in the glow plug circuit (broken, corroded, or loose)
3. Failed glow plug relay (responsible for supplying power to multiple glow plugs)
4. Open or short in the glow plug harness (damaged insulation or connectors)
5. PCM/ECM failure (rare, but possible if circuit checks out)
6. Blown fuse in the glow plug system

Step-by-Step Diagnostic for Code P0680 #

Diagnosing P0680 requires patience and basic electrical testing skills. Begin with the basics—don’t overlook blown fuses or simple connector issues. A digital multimeter (DMM) is your best friend here, as resistance and continuity checks are crucial. Always consult your vehicle’s wiring diagrams and OEM procedures for specific test values.

• 1. Visually inspect the glow plug harness and connectors at cylinder 10 for obvious damage, corrosion, or loose connections.
• 2. Check the fuse related to the glow plug system in the power distribution box.
• 3. Test the glow plug in cylinder 10 for resistance using a DMM. Compare the reading to OEM specs (typically 0.5–2.0 ohms). Infinite resistance indicates an open plug.
• 4. Check for voltage at the cylinder 10 glow plug connector during pre-glow phase (key ON, engine OFF, cold engine). You should see battery voltage briefly.
• 5. Test the glow plug relay by listening for a click on key ON and verifying voltage output.
• 6. Inspect wiring continuity from the relay/module to cylinder 10’s glow plug. Repair any opens or shorts found.
• 7. If all wiring and components test normal, test or reprogram the PCM/ECM as needed (rare).

Possible Repairs for Code P0680 #

The repair path for P0680 depends on the root cause identified during your diagnostic. Most repairs are straightforward—involving replacing faulty components or repairing damaged wiring. Using OEM parts is highly recommended to avoid premature failures.

• Replace the glow plug for cylinder 10 if it tests open or out of specification.
• Repair or replace wiring/connectors that are corroded, damaged, or loose in the glow plug circuit.
• Replace the glow plug relay if it fails to operate or supply correct voltage.
• Replace blown fuse and investigate the cause of overload before resetting the code.
• In rare cases, replace or reprogram the PCM/ECM (only after all other diagnostics are exhausted).

Can You Drive with Code P0680? #

Yes, but with limitations. P0680 does not typically cause immediate drivability failure, especially once the engine is warm. However, hard starting and rough running—especially in cold conditions—can worsen and lead to additional issues such as battery drain, increased emissions, or even injector problems. It’s best to address this code as soon as possible to avoid being stranded on a cold morning or causing further engine wear.

Vehicles Most Commonly Affected by Code P0680 #

P0680 is most often found on large displacement diesel engines—especially those with more than eight cylinders. It’s commonly reported in certain commercial vehicles, heavy-duty pickups, and European diesels where cylinder numbering includes a tenth cylinder.

• RAM/Cummins 6.7L I6 (with 10-cylinder variants)
• Ford Super Duty (F-650/750 with V10 diesel engines)
• Mercedes-Benz Sprinter/Actros (V10 & larger diesels)
• Isuzu and Iveco heavy-duty trucks
• Some off-road and industrial diesel applications

Common Mistakes & Best Practices for P0680 #

Mistakes in addressing P0680 often arise from skipping basic electrical checks or rushing to replace components without proper testing. Always use a systematic approach—guesswork can be costly in both time and parts.

• Do not replace all glow plugs blindly—test each plug and circuit individually.
• Always check fuses before suspecting more expensive components.
• Use dielectric grease on connectors after repairs to prevent future corrosion.
• Follow OEM wiring diagrams for accurate pinouts and test points.
• Clear the code and perform a cold start after repairs to confirm resolution.

FAQ Express: P0680 Cylinder 10 Glow Plug Circuit/Open #

Still have questions? Here are some quick answers to common concerns:

• Q: Will a bad glow plug affect engine performance once warm?
  A: Usually, no. Glow plugs are mainly for cold starting. Once the engine reaches operating temperature, their effect is minimal.
• Q: Can I use universal glow plugs?
  A: It’s strongly recommended to use OEM-specified glow plugs. Universal types may not match resistance or fitment, leading to repeat failures or improper operation.
• Q: Is it safe to clear the code without fixing the issue?
  A: Clearing the code without repair will not resolve the underlying fault. The code and symptoms will return, often at the worst time—like a cold morning.