P0672 Cylinder 2 Glow Plug Circuit

The P0672 trouble code is a generic OBD-II diagnostic trouble code related to the glow plug circuit for Cylinder 2 in a diesel engine.

P0672 – Cylinder 2 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 2.

Glow plugs help heat the combustion chamber during cold starts. When the ECM detects that the electrical characteristics of the Cylinder 2 glow plug circuit are outside the expected range, it stores P0672.

It is important to understand that P0672 does not automatically mean the Cylinder 2 glow plug itself is defective. The problem can also be caused by the wiring, connector, fuse, glow plug relay, glow plug control module, power supply, ground connection or ECM/PCM control circuit.

What Does P0672 Mean?

P0672 can be understood as:

P = Powertrain
0 = Generic OBD-II code
6 = Computer output/control-related fault
7 = Glow plug circuit designation
2 = Cylinder 2

The key description is:

Cylinder 2 Glow Plug Circuit

In simple terms:

The engine computer has detected an electrical fault in the circuit responsible for controlling the glow plug on Cylinder 2.

What Is a Glow Plug?

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

Unlike a gasoline spark plug, a glow plug does not create a spark to ignite the fuel mixture. Instead, its heating element becomes extremely hot and helps increase the temperature inside the combustion chamber.

This additional heat makes diesel fuel easier to ignite during cold starting.

Depending on the engine, the glow plugs may continue operating briefly after the engine starts. This helps improve combustion while the engine is warming up.

Why Are Glow Plugs Important?

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

When the engine is cold, the temperature produced by compression may not be sufficient for immediate and stable combustion.

Glow plugs help by:

• Heating the combustion chamber

• Improving cold starting

• Reducing cranking time

• Improving initial combustion

• Reducing white or gray smoke

• Reducing cold-start emissions

• Improving engine smoothness during warm-up

A faulty glow plug is therefore generally more noticeable during cold weather.

What Is Cylinder 2?

Cylinder 2 refers to the second cylinder according to the engine manufacturer's cylinder-numbering system.

The physical location of Cylinder 2 is not the same on every engine.

Different manufacturers use different cylinder numbering arrangements, so the correct location should be confirmed using manufacturer-specific service information before testing or replacing the glow plug.

Symptoms of P0672

Possible symptoms include:

• Check Engine Light

• Glow plug warning light

• Difficult cold starting

• Longer cranking time

• Rough idle after startup

• White or gray exhaust smoke

• Cold-start hesitation

• Uneven combustion during warm-up

• Increased emissions

• Increased fuel consumption during repeated cold starts

In warmer temperatures, the vehicle may start and operate almost normally.

Can P0672 Cause a No-Start?

It can, depending on the engine and ambient temperature.

Many modern diesel engines can start with one defective glow plug under moderate conditions.

However, very low temperatures can make glow plug operation much more important.

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

Is P0672 Serious?

P0672 should be diagnosed and repaired, although it is not always an immediate emergency.

A single defective glow plug may have little effect after the engine reaches normal operating temperature.

However, leaving the fault unresolved can result in:

• Difficult cold starts

• Increased exhaust smoke

• Poor cold combustion

• Increased emissions

• Additional battery load

• Additional starter load

The fault is especially worth addressing before winter or extended periods of cold weather.

Common Causes of P0672

Failed Cylinder 2 glow plug

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

Damaged glow plug wiring

The wire supplying Cylinder 2 may be broken, shorted or damaged.

Loose connector

A loose terminal can interrupt the electrical connection.

Corroded connector

Corrosion can increase resistance and reduce current flow.

Faulty glow plug control module

Modern diesel engines often use an electronic controller to operate individual glow plugs.

Faulty glow plug relay

Some vehicles use a conventional relay to provide power to the glow plugs.

Blown fuse

A blown fuse can interrupt the glow plug power supply.

Poor electrical ground

A poor ground connection can interfere with glow plug operation.

Damaged engine wiring harness

Heat, vibration, oil and moisture can damage the wiring.

Low system voltage

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

ECM/PCM control problem

The ECM/PCM may control the glow plug circuit directly or communicate with a separate glow plug controller.

Can a Bad Glow Plug Cause P0672?

Yes.

A defective Cylinder 2 glow plug is one of the first things that should be tested.

Possible glow plug failures include:

• Open internal heating element

• Excessive resistance

• Internal electrical damage

• Age-related failure

• Thermal damage

However, replacing the glow plug without checking the rest of the circuit can result in an incorrect repair.

Can a Bad Glow Plug Control Module Cause P0672?

Yes.

If the glow plug controller cannot correctly operate the Cylinder 2 circuit, the ECM may detect an abnormal electrical condition.

If multiple cylinder-specific glow plug codes appear at the same time, investigate the common controller, power supply, ground and wiring before replacing individual glow plugs.

Can a Bad Glow Plug Relay Cause P0672?

Yes, on vehicles equipped with a conventional glow plug relay.

A defective relay may prevent the glow plug from receiving the required electrical supply.

Newer diesel engines may use an electronic glow plug control module instead of a conventional relay.

Can a Blown Fuse Cause P0672?

Yes.

If the fuse supplying the glow plug system is blown, the glow plug may not receive the required power.

If a replacement fuse fails again, the underlying electrical problem must be found rather than repeatedly replacing the fuse.

Can Wiring Cause P0672?

Yes.

Wiring should always be inspected when diagnosing a glow plug circuit code.

Look for:

• Broken wires

• Chafed insulation

• Melted wiring

• Corroded terminals

• Loose connectors

• Oil contamination

• Water intrusion

• Poor previous repairs

Glow plug wiring is exposed to high engine temperatures, so heat damage is particularly important.

Can a Weak Battery Cause P0672?

Potentially, yes.

Glow plugs can draw significant current.

A weak battery can cause lower system voltage during cold starting and reduce glow plug effectiveness.

However, a weak battery does not necessarily mean that the Cylinder 2 glow plug circuit itself is defective.

If several glow plug codes are present, the battery and charging system should be tested along with the glow plug system.

Can a Bad Alternator Cause P0672?

Potentially, indirectly.

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

Check:

• Battery condition

• Charging voltage

• Alternator output

• Voltage stability

before replacing a glow plug controller or ECM.

Can P0672 Cause White Smoke?

Yes, potentially.

If Cylinder 2 does not receive sufficient heating during a cold start, fuel may not burn completely.

This can produce temporary white or gray exhaust smoke.

If the smoke continues after the engine reaches operating temperature, other problems should be investigated, including:

• Fuel injector problems

• Low compression

• Incorrect injection timing

• Coolant entering the combustion chamber

Can P0672 Cause Rough Running?

Yes, especially immediately after a cold start.

Insufficient heating in Cylinder 2 can contribute to incomplete combustion.

The engine may:

• Shake

• Run unevenly

• Produce smoke

• Hesitate

• Improve as it warms up

How to Diagnose P0672

A systematic diagnostic procedure is recommended.

1. Scan all diagnostic codes

Look for additional codes involving:

• Other glow plugs

• Glow plug control module

• Battery voltage

• Engine coolant temperature

• Fuel injection

• Misfire or combustion

• ECM/PCM communication

If several glow plug codes are present, investigate common components first.

2. Identify Cylinder 2

Confirm the physical location of Cylinder 2 using manufacturer-specific service information.

3. Inspect the Cylinder 2 glow plug

Look for:

• Physical damage

• Corrosion

• Carbon deposits

• Damaged terminal

• Signs of overheating

4. Inspect the connector

Check for:

• Loose terminals

• Corroded terminals

• Bent pins

• Broken locking mechanism

• Oil contamination

• Water intrusion

5. Test glow plug resistance

Measure the Cylinder 2 glow plug according to manufacturer specifications.

Comparison with the other glow plugs can also be useful.

A defective glow plug may show:

• Open circuit

• Excessively high resistance

• A significantly different reading from the other glow plugs

Because modern glow plugs can have very low resistance, test equipment accuracy and manufacturer specifications are important.

6. Check the power supply

Verify whether the Cylinder 2 glow plug receives the required electrical supply when the glow system is activated.

Do not assume that every modern glow plug receives constant battery voltage. Some systems use electronically controlled or variable voltage.

7. Check current draw

Current testing can help determine whether the glow plug is operating correctly.

An abnormal current pattern can indicate:

• Open glow plug

• High-resistance connection

• Short circuit

• Controller problem

8. Test the glow plug controller

If the vehicle is equipped with an electronic controller, check:

• Power supply

• Ground

• Command signals

• Cylinder 2 output

• Communication

9. Test the glow plug relay

If the vehicle uses a conventional relay, verify:

• Coil operation

• Contact operation

• Power supply

• Output voltage

10. Check the fuse

Inspect the relevant glow plug system fuse or fuses.

If a fuse repeatedly fails, find the underlying cause.

11. Inspect the wiring harness

Trace the Cylinder 2 circuit from the glow plug to the controller.

Pay particular attention to areas near:

• Exhaust components

• Turbocharger

• Cylinder head

• High-temperature surfaces

• Harness brackets

12. Check grounds

Inspect relevant engine, chassis and controller grounds.

13. Check engine temperature data

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

An inaccurate coolant-temperature signal can affect glow plug operation.

14. Check ECM/PCM control

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

How to Test a Glow Plug

The exact test procedure depends on the engine.

A basic approach is to compare the Cylinder 2 glow plug with other glow plugs of the same specification.

Possible checks include:

• Resistance

• Power supply

• Current draw

• Physical condition

Do not automatically connect a modern glow plug directly to a battery.

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

Why Comparing Glow Plugs Can Help

When several glow plugs have the same specification, comparison can help identify an abnormal component.

For example, if the other glow plugs have similar electrical characteristics while Cylinder 2 shows an open circuit or a significantly different reading, Cylinder 2 becomes a strong suspect.

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

Can P0672 Affect Fuel Economy?

Potentially, especially during cold operation.

A single defective glow plug generally has little effect on fuel consumption after the engine is fully warmed up.

However, repeated difficult starting and incomplete combustion during warm-up can increase fuel consumption and emissions.

Can P0672 Damage the Engine?

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

The more common consequences are:

• Difficult starting

• Increased smoke

• Poor cold combustion

• Increased emissions

• Additional starter and battery load

A glow plug that physically breaks or suffers mechanical damage is a separate issue and can potentially create more serious mechanical problems.

Can the Coolant Temperature Sensor Cause P0672?

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

The ECM uses coolant temperature to determine when and how long to activate the glow plugs.

If the temperature signal is incorrect, glow plug activation may be inappropriate.

However, when P0672 is stored, the actual Cylinder 2 electrical circuit should still be tested.

Can P0672 Return After Clearing the Code?

Yes.

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

Clearing the code removes the stored diagnostic information but does not repair the problem.

Should You Replace Only the Cylinder 2 Glow Plug?

If testing confirms that the Cylinder 2 glow plug has failed and the rest of the circuit is functioning correctly, replacing that glow plug may resolve P0672.

However, if all glow plugs have similar age and mileage, replacing them as a set may be considered.

The decision depends on:

• Manufacturer recommendations

• Vehicle mileage

• Engine design

• Glow plug condition

• Service history

Common Diagnostic Mistakes With P0672

Replacing the glow plug without testing the circuit

The wiring or controller may actually be defective.

Assuming the location of Cylinder 2

Cylinder numbering varies between engines.

Ignoring the glow plug controller

Modern diesel systems may use sophisticated electronic control.

Installing the wrong glow plug

Glow plugs can differ in:

• Voltage

• Resistance

• Heating characteristics

• Length

• Thread size

Applying direct battery voltage without checking specifications

This can damage certain 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, fuse, relay/controller, power supply and grounds should be tested first.

What Is the Correct Repair for P0672?

The correct repair depends on the confirmed cause.

Possible repairs include:

• Replacing the Cylinder 2 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 an ECM/PCM control signal

• Updating ECM software where applicable

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

How to Test the Vehicle After Repair

After completing the repair, verify:

• Cylinder 2 glow plug operation

• Glow plug controller operation

• Power supply

• Ground connections

• Current draw

• Engine coolant temperature data

• Cold-start performance

• Exhaust smoke

• Diagnostic trouble codes

Clear the code and perform several cold-start cycles.

The engine should start normally and operate smoothly during warm-up, and P0672 should not return.

Frequently Asked Questions About P0672

What does P0672 mean?

P0672 means the ECM/PCM has detected an electrical problem in the Cylinder 2 glow plug circuit.

Does P0672 mean the glow plug is bad?

Not necessarily. The wiring, connector, fuse, relay, glow plug controller or ECM/PCM control circuit can also cause the code.

Can P0672 cause hard starting?

Yes, particularly in cold weather.

Can P0672 cause a no-start?

It can, especially in extremely cold conditions or when multiple glow plugs are defective.

Can P0672 cause white smoke?

Yes. Insufficient glow-plug heating can contribute to incomplete combustion and temporary white or gray smoke during cold startup.

Can P0672 cause rough running?

Yes, particularly during the first moments after a cold start.

Can a bad glow plug controller cause P0672?

Yes.

Can a blown fuse cause P0672?

Yes, if the fuse interrupts power to the glow plug system.

Can wiring cause P0672?

Yes.

Can a weak battery cause P0672?

A weak battery can contribute to poor glow-plug performance and difficult starting, although it does not necessarily mean that the Cylinder 2 circuit itself is defective.

Can I drive with P0672?

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

Should I replace all glow plugs?

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

Should I replace the ECM/PCM for P0672?

No. The glow plug, wiring, fuse, relay or glow plug control module should be tested before considering an ECM/PCM problem.

Final Thoughts on P0672

P0672 – Cylinder 2 Glow Plug Circuit indicates that the ECM/PCM has detected an electrical problem associated with the glow plug circuit for Cylinder 2.

The main areas to investigate are:

• Cylinder 2 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 2 → 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 P0672 is a circuit fault, not simply a "bad glow plug" code. Testing the complete Cylinder 2 circuit is the best way to identify the actual cause and avoid unnecessary parts replacement.