P0680 Cylinder 10 Glow Plug Circuit

The P0680 trouble code is a generic OBD-II diagnostic trouble code associated with the glow plug circuit for Cylinder 10 in a diesel engine.

P0680 – Cylinder 10 Glow Plug Circuit

This code means that the engine control module (ECM/PCM) has detected an electrical problem in the glow plug circuit associated with Cylinder 10.

Glow plugs help diesel engines start by heating the combustion chamber during cold-start conditions. If the ECM detects that the Cylinder 10 glow plug circuit has an abnormal electrical condition, it stores P0680.

The important point is that P0680 does not automatically mean the glow plug itself has failed. The fault can also be caused by the wiring, connector, fuse, glow plug relay, glow plug control module or the ECM/PCM control circuit.

What Does P0680 Mean?

P0680 can be understood as:

P = Powertrain
0 = Generic OBD-II code
6 = Computer output/control-related fault
8 = Glow plug system
0 = Cylinder 10 circuit

The key phrase is:

Cylinder 10 Glow Plug Circuit

In simple terms:

The engine computer has detected an electrical problem in the circuit controlling the glow plug for Cylinder 10.

What Is a Glow Plug?

A glow plug is an electrically heated component used in diesel engines.

A gasoline spark plug creates a spark to ignite the air-fuel mixture. A diesel glow plug works differently.

It heats up to a very high temperature and helps provide sufficient heat inside the combustion chamber for reliable combustion during cold starting.

Depending on the engine, glow plugs may also remain active briefly after the engine starts.

Why Are Glow Plugs Important?

Diesel engines depend on compression-generated heat to ignite fuel.

When the engine is cold, the compressed air may not reach an ideal temperature quickly enough for reliable combustion.

Glow plugs help by:

• Heating the combustion chamber

• Improving cold starting

• Reducing cranking time

• Improving initial combustion

• Reducing white smoke

• Reducing cold-start emissions

• Improving engine operation immediately after startup

A failed glow plug can therefore become especially noticeable during cold weather.

What Is Cylinder 10?

Cylinder 10 refers to the cylinder associated with the tenth glow plug circuit.

This code is mainly relevant to engines with ten or more cylinders or specific engine configurations where the manufacturer identifies a Cylinder 10 glow plug circuit.

The physical location of Cylinder 10 is not universal.

Cylinder numbering can vary between engine manufacturers and configurations, so the correct cylinder should always be confirmed using the vehicle's service information.

Symptoms of P0680

Possible symptoms include:

• Check Engine Light

• Glow plug warning light

• Difficult cold starting

• Extended cranking

• Rough running after cold startup

• White or gray exhaust smoke

• Poor cold-start combustion

• Engine hesitation when cold

• Increased cold-start emissions

• Reduced fuel economy in some situations

In warm weather, the vehicle may start and drive almost normally despite the stored code.

Can P0680 Cause a No-Start?

Yes, but it depends on the engine and temperature.

A modern diesel engine can often start with one defective glow plug when temperatures are moderate.

However, extremely cold conditions can make glow plugs much more important.

If several glow plugs are faulty or the glow plug control system has a broader problem, starting can become extremely difficult or impossible.

Is P0680 Serious?

It should be diagnosed and repaired, although the immediate severity varies.

One defective glow plug may not cause serious drivability problems once the engine is warm.

However, leaving the problem unresolved can result in:

• Difficult cold starts

• Increased exhaust smoke

• Poor cold combustion

• Increased emissions

• Greater battery load

• Greater starter load

The problem becomes particularly important before winter or in very cold climates.

Common Causes of P0680

Failed Cylinder 10 glow plug

The glow plug may have an open circuit, excessive resistance or internal damage.

Damaged glow plug wiring

The wire supplying the Cylinder 10 glow plug may be broken, shorted or damaged.

Loose connector

A poor electrical connection can prevent the glow plug from operating correctly.

Corroded connector

Corrosion can increase resistance in the circuit.

Faulty glow plug control module

Many modern diesel engines use an electronic glow plug controller.

Faulty glow plug relay

Some systems use a conventional relay to supply power.

Blown fuse

A fuse failure can interrupt the glow plug power supply.

Poor electrical ground

Depending on the system design, poor grounding can interfere with glow plug operation.

Engine harness damage

Glow plug wiring is exposed to high temperatures and engine vibration.

Low system voltage

Battery or charging-system problems can affect glow plug operation.

ECM/PCM control problem

The engine computer may control the glow plug system directly or communicate with a dedicated controller.

Can a Bad Glow Plug Cause P0680?

Yes.

A defective Cylinder 10 glow plug is one of the first things to test.

A glow plug can fail due to:

• Open internal heating element

• Excessive resistance

• Internal electrical damage

• Age

• Repeated thermal cycling

However, replacing the glow plug without testing the rest of the circuit can lead to an incorrect repair.

Can a Glow Plug Control Module Cause P0680?

Yes.

If the control module cannot correctly supply or control the Cylinder 10 circuit, the ECM may detect an abnormal condition and store P0680.

If codes for several cylinders appear simultaneously, the common controller, power supply or wiring should be investigated before replacing individual glow plugs.

Can a Glow Plug Relay Cause P0680?

Yes, if the vehicle uses a conventional glow plug relay.

A defective relay can prevent the glow plug system from receiving the correct electrical supply.

However, many newer diesel engines use electronic glow plug control modules instead of a simple relay.

Can a Blown Fuse Cause P0680?

Yes.

If the fuse supplying the glow plug system is blown, the required voltage or current may not reach the glow plug.

Always determine why a fuse has blown if it fails again after replacement.

Can Wiring Cause P0680?

Yes.

Wiring problems are an important possible cause.

Inspect for:

• Broken wires

• Chafed insulation

• Melted insulation

• Corroded terminals

• Loose connectors

• Oil contamination

• Water intrusion

• Previous wiring repairs

Because glow plug wiring operates in a hot engine environment, heat damage should receive particular attention.

Can a Weak Battery Cause P0680?

Potentially, yes.

Glow plugs can consume significant electrical current.

A weak battery can result in lower system voltage during cold starting and make glow-plug operation less effective.

However, a weak battery does not necessarily mean that the Cylinder 10 circuit itself has failed.

If several glow plug codes are stored, test the battery and charging system along with the glow plug system.

Can a Bad Alternator Cause P0680?

Potentially, indirectly.

An alternator that produces insufficient or unstable voltage can affect glow plug operation and other electrical systems.

Check:

• Battery condition

• Charging voltage

• Alternator output

• Voltage stability

before condemning the glow plug controller or ECM.

Can P0680 Cause White Smoke?

Yes, potentially.

If Cylinder 10 does not receive sufficient heating during a cold start, fuel may not burn completely.

This can produce temporary white or gray smoke.

If the smoke continues after the engine warms up, other causes should be investigated, including:

• Fuel injector problems

• Low compression

• Coolant entering the combustion chamber

• Incorrect injection timing

Can P0680 Cause Rough Running?

Yes, particularly during cold startup.

If Cylinder 10 does not achieve proper combustion during the first moments after starting, the engine may:

• Shake

• Run unevenly

• Produce smoke

• Hesitate

• Improve as the engine warms

How to Diagnose P0680

A complete circuit diagnosis is preferable to simply replacing the glow plug.

1. Scan all modules

Look for other codes involving:

• Other glow plugs

• Glow plug control

• Battery voltage

• Engine coolant temperature

• Fuel injection

• Engine misfire

• ECM/PCM communication

Multiple glow plug codes can indicate a common problem.

2. Identify Cylinder 10

Confirm the cylinder location using the manufacturer's engine documentation.

Do not rely on a generic cylinder-numbering assumption.

3. Inspect the Cylinder 10 glow plug

Look for:

• Physical damage

• Corrosion

• Carbon deposits

• Terminal damage

• Signs of overheating

4. Inspect the connector

Check for:

• Loose connection

• Corroded terminals

• Bent pins

• Broken locking mechanism

• Oil contamination

• Water intrusion

5. Test glow plug resistance

Measure the Cylinder 10 glow plug according to manufacturer specifications.

Compare it with the other glow plugs when appropriate.

A failed glow plug may show:

• Open circuit

• Excessively high resistance

• An abnormal reading compared with the other glow plugs

Because many modern glow plugs have very low resistance, measurement technique and the manufacturer's specification are important.

6. Check power at the glow plug

Determine whether the Cylinder 10 glow plug receives the required electrical supply when the glow system is activated.

The exact voltage depends on the vehicle.

Some modern systems use variable or electronically controlled voltage rather than a simple battery-voltage supply.

7. Check current draw

Current measurement can provide additional information about glow plug operation.

An abnormal current pattern can indicate:

• Open glow plug

• High-resistance connection

• Short circuit

• Controller problem

8. Test the glow plug controller

If equipped, check:

• Power supply

• Ground

• Control signals

• Cylinder 10 output

• Communication

9. Test the glow plug relay

On relay-based systems, verify:

• Relay coil

• Relay contacts

• Power supply

• Output voltage

10. Check the fuse

Inspect all relevant glow plug fuses.

A fuse that repeatedly blows indicates another electrical problem.

11. Inspect the wiring harness

Trace the Cylinder 10 circuit between the glow plug and controller.

Pay particular attention to wiring near:

• Exhaust components

• Turbocharger

• Cylinder head

• High-temperature areas

• Harness brackets

12. Check grounds

Verify the required engine, chassis and controller grounds.

13. Check engine temperature data

The ECM uses engine temperature information to determine glow plug activation.

An incorrect coolant-temperature reading can affect glow plug operation.

14. Check ECM/PCM control

If the glow plug, wiring, controller, power supply and grounds are good, investigate the ECM/PCM command circuit.

How to Test a Glow Plug

The correct procedure depends on the engine.

A basic diagnostic approach is to compare the Cylinder 10 glow plug with other glow plugs of the same type.

Check:

• Resistance

• Power supply

• Current draw

• Physical condition

Do not automatically apply battery voltage directly to a glow plug.

Some modern glow plugs are designed for specific voltage levels and electronic control strategies. Applying incorrect voltage can damage the component.

Why Comparing Glow Plugs Helps

If several glow plugs are the same specification, comparison can help identify an abnormal component.

For example, if most glow plugs have similar electrical characteristics but Cylinder 10 shows an open circuit or substantially different reading, the Cylinder 10 glow plug becomes a strong suspect.

However, manufacturer specifications should always take priority over simple comparison.

Can P0680 Affect Fuel Economy?

Potentially, but usually not significantly once the engine is warm.

A single failed glow plug generally has a greater effect on cold-start operation than normal warm-engine driving.

Repeated difficult starts and incomplete cold combustion can increase fuel consumption and emissions.

Can P0680 Damage the Engine?

A basic glow plug circuit fault does not normally cause immediate major engine damage.

The main consequences are:

• Difficult starting

• Increased smoke

• Poor cold combustion

• Increased emissions

• Additional starter and battery load

However, if a glow plug physically breaks or its tip becomes damaged, a separate mechanical risk may exist.

Can the Coolant Temperature Sensor Cause P0680?

It can affect glow plug operation, but it is not the first thing to suspect for a cylinder-specific circuit code.

The ECM uses coolant temperature to determine whether and how long the glow plugs should operate.

An incorrect temperature signal can cause inappropriate glow-plug activation.

Nevertheless, if P0680 is stored, the actual Cylinder 10 electrical circuit should be tested first.

Can P0680 Return After Clearing?

Yes.

If the underlying electrical problem remains, the ECM can detect the fault again during a subsequent glow-plug activation.

Clearing the code only removes the stored diagnostic information.

Should You Replace Only the Cylinder 10 Glow Plug?

If testing confirms that Cylinder 10's glow plug has failed and the rest of the circuit is functioning correctly, replacing that glow plug may solve the problem.

However, if the other glow plugs are also old or their electrical characteristics are deteriorating, replacing the complete set may be considered.

The best approach depends on:

• Manufacturer recommendations

• Glow plug condition

• Vehicle mileage

• Engine design

• Service history

Common Diagnostic Mistakes With P0680

Replacing the glow plug without testing the circuit

The wiring or controller may actually be defective.

Assuming the location of Cylinder 10

Cylinder numbering varies between engines.

Ignoring the glow plug controller

Modern diesel engines may use sophisticated electronic control.

Using an incorrect glow plug

Glow plugs can differ in:

• Voltage

• Resistance

• Heating characteristics

• Length

• Thread size

Applying battery voltage without checking specifications

This can damage some modern glow plugs.

Ignoring wiring damage

High engine temperatures can damage the glow plug harness.

Testing only resistance

Resistance testing is useful but does not necessarily prove complete glow plug performance.

Replacing the ECM immediately

The glow plug, wiring, controller, relay, fuse and power supply should be tested first.

What Is the Correct Repair for P0680?

The correct repair depends on the actual cause.

Possible repairs include:

• Replacing the Cylinder 10 glow plug

• Repairing the glow plug wiring

• Repairing or replacing the connector

• Replacing a faulty glow plug relay

• Replacing the glow plug control module

• Repairing a blown fuse or power supply

• Repairing poor ground connections

• Repairing damaged engine wiring

• Correcting a control signal problem

• Updating ECM software where applicable

• Replacing the ECM/PCM only when its control circuit is confirmed faulty

How to Test the Vehicle After Repair

After repairing P0680, verify:

• Cylinder 10 glow plug operation

• Glow plug controller operation

• Power supply

• Ground connections

• Current draw

• Engine coolant temperature data

• Cold-start performance

• Exhaust smoke

• Stored diagnostic codes

Clear the code and perform several cold-start cycles.

The engine should start normally and run smoothly during warm-up, and P0680 should not return.

Frequently Asked Questions About P0680

What does P0680 mean?

P0680 means the ECM/PCM has detected an electrical problem in the Cylinder 10 glow plug circuit.

Does P0680 mean the glow plug is bad?

Not necessarily. The wiring, connector, relay, control module or ECM/PCM circuit can also cause the code.

Can P0680 cause hard starting?

Yes, especially in cold temperatures.

Can P0680 cause a no-start?

It can, particularly in very cold conditions or if other glow plugs are also faulty.

Can P0680 cause white smoke?

Yes. Inadequate glow-plug heating can cause incomplete cold combustion and temporary white or gray smoke.

Can P0680 cause rough running?

Yes, particularly immediately after a cold start.

Can a bad glow plug controller cause P0680?

Yes.

Can a blown fuse cause P0680?

Yes, if the fuse interrupts the glow plug power supply.

Can wiring cause P0680?

Yes.

Can a weak battery cause P0680?

A weak battery can contribute to poor glow-plug performance and difficult starting, although it does not necessarily mean the Cylinder 10 circuit itself has failed.

Can I drive with P0680?

If the engine starts and runs normally, the vehicle may remain driveable, but the problem should be repaired. Cold-weather starting may become significantly more difficult.

Should I replace all glow plugs?

Not automatically. Test them individually and follow the manufacturer's recommendations.

Should I replace the ECM/PCM for P0680?

No. The glow plug, wiring, fuse, relay or glow plug controller should be tested before considering an ECM/PCM fault.

Final Thoughts on P0680

P0680 – Cylinder 10 Glow Plug Circuit indicates that the engine control module has detected an electrical problem in the glow plug circuit associated with Cylinder 10.

The main areas to investigate are:

• Cylinder 10 glow plug

• Glow plug connector

• Wiring harness

• Glow plug relay

• Glow plug control module

• Fuse

• Power supply

• Ground connections

• ECM/PCM control circuit

A logical diagnostic sequence is:

Scan All Codes → Identify Cylinder 10 → Inspect Glow Plug and Connector → Test Glow Plug → Check Power Supply → Check Current Draw → Test Glow Plug Controller/Relay → Inspect Wiring → Check Fuse and Grounds → Verify Temperature Data → Test ECM/PCM Control

The key point is that P0680 is a circuit fault, not simply a "bad glow plug" code. Testing the complete Cylinder 10 circuit is the best way to identify the actual cause and avoid unnecessary parts replacement.