P0673 Cylinder 3 Glow Plug Circuit

The P0673 – Cylinder 3 Glow Plug Circuit diagnostic trouble code (DTC) indicates that the engine control system has detected an electrical problem in the glow plug circuit for cylinder 3.

This code is primarily associated with diesel engines. P0673 is a cylinder-specific code, meaning the control system has identified a problem with the glow plug circuit assigned to cylinder 3, rather than simply reporting a general glow plug system fault.

The actual problem may be the glow plug, wiring, electrical connector, fuse, glow plug relay, or glow plug control module.

What Does P0673 Mean?

In simple terms:

The engine control module has detected abnormal electrical behavior in the cylinder 3 glow plug circuit.

A simplified circuit can be thought of as:

Battery → Fuse → Glow Plug Control Module/Relay → Cylinder 3 Glow Plug

When the ECM or PCM activates the glow plug system, it monitors the electrical response.

If the expected current, voltage, or circuit behavior is not detected, the system can store P0673.

The fault may involve:

• Open circuit

• Short circuit

• Excessive resistance

• Incorrect current draw

• Poor electrical connection

• Failed glow plug

What Is a Glow Plug?

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

It does not create a spark like a gasoline spark plug. Instead, its heating element becomes extremely hot and helps increase the temperature inside the combustion chamber.

This makes it easier for diesel fuel to ignite when the engine is cold.

On some modern diesel engines, glow plugs can continue operating for a short period after startup to improve combustion and reduce emissions.

What Does the Cylinder 3 Glow Plug Do?

The cylinder 3 glow plug provides additional heat inside cylinder 3 during cold starting.

The engine control system determines when and for how long the glow plug should operate.

If the circuit fails, cylinder 3 may not receive sufficient preheating.

The engine can still start normally in warm conditions, which means the problem may become much more obvious during cold weather.

What Causes P0673?

Possible causes include:

• Failed cylinder 3 glow plug

• Open circuit

• Shorted circuit

• Damaged wiring

• Corroded connector

• Loose electrical terminal

• Excessive circuit resistance

• Faulty glow plug relay

• Faulty glow plug control module

• Blown fuse

• Poor power connection

• Poor ground connection

• Damaged glow plug terminal

The actual cause should be confirmed through testing rather than assumed from the code alone.

Can a Bad Glow Plug Cause P0673?

Yes.

A defective cylinder 3 glow plug is one of the first things that should be checked.

The internal heating element can fail because of:

• Open circuit

• Excessive resistance

• Internal electrical damage

• Age

• Excessive heat

However, replacing the glow plug immediately is not always the correct repair. The wiring and control circuit should also be tested.

Can Broken Wiring Cause P0673?

Yes.

A broken wire between the glow plug controller and cylinder 3 can prevent the glow plug from receiving the required electrical current.

Inspect the harness for:

• Broken wires

• Chafing

• Melted insulation

• Corrosion

• Pinched sections

• Poor previous repairs

High engine temperatures and vibration can contribute to wiring damage.

Can a Bad Connector Cause P0673?

Yes.

A loose or corroded connector can create excessive resistance or interrupt the circuit.

Inspect the cylinder 3 connector for:

• Corrosion

• Loose terminals

• Burn marks

• Bent contacts

• Water contamination

• Poor terminal tension

Can a Blown Fuse Cause P0673?

Yes, depending on the vehicle.

Some diesel engines use dedicated glow plug fuses or high-current protection.

If the fuse is blown, the reason for the failure should be investigated before installing another fuse.

Can a Bad Glow Plug Relay Cause P0673?

Yes, on systems that use a conventional relay.

Some diesel engines use a relay to control several glow plugs.

Modern systems may instead use an electronic Glow Plug Control Module (GPCM) that can control and monitor individual glow plug circuits.

Can a Bad Glow Plug Control Module Cause P0673?

Yes.

A defective control module may fail to provide the correct current or control signal to cylinder 3.

However, if P0673 is the only glow plug code stored, it is generally sensible to check the cylinder 3 glow plug, connector, and wiring before replacing the control module.

Can Low Battery Voltage Cause P0673?

Yes, potentially.

Glow plugs can draw considerable electrical current.

A weak battery or excessive voltage drop during starting can affect the glow plug system.

Check:

• Battery condition

• Battery voltage

• Cranking voltage

• Charging voltage

Can a Bad Alternator Cause P0673?

Potentially, but it is less likely when only cylinder 3 is affected.

A charging problem normally affects the vehicle's electrical system more broadly.

If multiple glow plug circuits or voltage-related codes are present, the charging system should be inspected.

Symptoms of P0673

Possible symptoms include:

• Check Engine Light

• Glow plug warning light

• Difficult cold starting

• Longer cranking time

• Rough idle after startup

• Engine vibration

• White smoke

• Increased emissions

• Poor cold-start performance

Once the engine is warm, the symptoms may become much less noticeable.

Can P0673 Cause a No-Start Condition?

Usually not by itself.

A single failed glow plug generally does not prevent a modern diesel engine from starting in moderate temperatures.

A more serious starting problem may occur when:

• Several glow plugs have failed

• Temperatures are extremely low

• Battery voltage is low

• Engine compression is poor

• There are additional fuel-system problems

Can P0673 Cause Hard Starting?

Yes, especially in cold weather.

Without sufficient heating in cylinder 3, combustion may be less efficient during the first few engine cycles.

This can cause:

• Longer cranking

• Rough startup

• Uneven combustion

• Temporary engine vibration

Can P0673 Cause White Smoke?

Yes.

If the combustion chamber is too cold, diesel fuel may not burn completely during startup.

The unburned fuel can produce white or light-colored smoke from the exhaust.

Can P0673 Cause Rough Idle?

Yes, particularly when the engine is cold.

If cylinder 3 does not receive adequate glow plug assistance, combustion in that cylinder may be weaker immediately after startup.

This can result in:

• Rough idle

• Engine vibration

• Uneven combustion

• Temporary misfire-like symptoms

Can P0673 Affect Fuel Economy?

Potentially.

A single glow plug failure normally has little effect once the engine is fully warmed up.

However, repeated difficult starts and incomplete cold combustion can increase fuel consumption and emissions.

Is P0673 Related to the Fuel Injector?

Not directly.

P0673 identifies a problem with the cylinder 3 glow plug circuit.

A faulty fuel injector can also cause rough running, smoke, or difficult starting, but it normally generates different diagnostic codes.

If the glow plug circuit tests correctly and the engine still runs poorly, the injector and other engine systems should be investigated separately.

How Is P0673 Diagnosed?

A systematic diagnosis is recommended.

1. Scan for all DTCs

Check for:

• Other glow plug codes

• Injector codes

• Voltage-related codes

• Communication codes

• Engine performance codes

If multiple glow plug codes are present, investigate the common power supply and control system.

2. Inspect the cylinder 3 glow plug

Check its physical condition and electrical connection.

3. Test glow plug resistance

Measure the resistance according to the manufacturer's specifications.

There is no universal resistance value for every diesel glow plug.

4. Check the wiring

Inspect the complete circuit between cylinder 3 and the glow plug controller.

5. Inspect the connector

Look for corrosion, loose terminals, heat damage, and poor terminal tension.

6. Check the fuse

Verify the appropriate glow plug fuse or high-current protection device.

7. Check control-module power and ground

Confirm that the glow plug controller receives the correct power and has a reliable ground.

8. Check the control signal

Verify that the controller is correctly commanding cylinder 3.

9. Test the glow plug control module

If the glow plug and wiring are good, the control module may require further diagnosis.

Can a Multimeter Diagnose P0673?

Yes.

A multimeter can be used to check:

• Glow plug resistance

• Circuit continuity

• Supply voltage

• Voltage drop

• Fuse condition

• Ground quality

However, modern glow plug systems may use PWM or electronically regulated current, so a basic voltage measurement may not provide a complete diagnosis.

Can a Clamp Meter Help?

Yes.

A suitable current clamp can measure the current drawn by the cylinder 3 glow plug.

This can help determine whether the glow plug is actually receiving and drawing the expected current.

Can an Oscilloscope Help?

Yes.

An oscilloscope can be useful for advanced diagnosis.

It can reveal:

• PWM control signals

• Missing control signals

• Abnormal voltage patterns

• Irregular current behavior

This can be particularly useful when a standard multimeter cannot clearly identify the fault.

What If P0673 Appears With Other Glow Plug Codes?

This is an important diagnostic clue.

If only P0673 is stored, focus first on:

Cylinder 3 glow plug → Connector → Wiring → Individual control circuit

If several glow plug codes are stored simultaneously, investigate:

• Glow plug control module

• Main power supply

• Ground

• Fuse

• Battery voltage

• Glow plug relay

A common electrical problem may be affecting multiple cylinders.

What If P0673 Appears With P0670?

P0670 generally concerns the glow plug control module/control circuit, while P0673 identifies the cylinder 3 glow plug circuit.

If both codes are present, check the control module's power, ground, and main wiring before replacing individual glow plugs.

What If P0673 Appears Only in Cold Weather?

This is a useful diagnostic clue.

A weak glow plug or marginal electrical connection may function adequately in mild weather but fail to provide sufficient heat during a cold start.

Cold-weather symptoms can include:

• Longer cranking

• Rough startup

• White smoke

• Engine vibration

What If P0673 Appears After Glow Plug Replacement?

Verify:

• Correct glow plug type

• Correct voltage rating

• Proper installation

• Connector seating

• Terminal condition

• Wiring condition

A glow plug that physically fits may still have incorrect electrical characteristics.

What If P0673 Returns Immediately After Clearing?

If the code returns immediately, the fault is probably still present.

Focus on:

• Open glow plug

• Shorted circuit

• Broken wire

• Poor connector

• Control-module output

If the problem occurs only under specific temperatures, further cold-start testing may be necessary.

What If P0673 Appears After Engine Repair?

Inspect the wiring around cylinder 3 carefully.

Engine repairs can result in:

• Disconnected connectors

• Pinched wires

• Damaged harnesses

• Loose grounds

• Incorrectly routed wiring

Is P0673 a Serious Code?

Usually, P0673 is not an immediate engine-damage emergency.

However, it should be repaired because it can cause:

• Difficult cold starts

• Longer cranking

• Increased starter load

• Increased battery load

• Rough cold operation

• Increased emissions

• White smoke

The problem becomes more important as ambient temperatures fall.

Can You Drive With P0673?

Usually, yes, if the engine starts and runs normally.

A single glow plug circuit fault generally does not prevent normal driving.

However, the problem should not be ignored for an extended period, especially if:

• Cold starting becomes difficult

• Several glow plug codes are present

• Excessive smoke appears

• The engine runs very roughly after startup

How Is P0673 Repaired?

The repair depends on the confirmed cause.

Possible repairs include:

• Replacing the cylinder 3 glow plug

• Repairing damaged wiring

• Repairing the connector

• Replacing damaged terminals

• Repairing a fuse or power supply

• Replacing the glow plug relay

• Replacing the glow plug control module

• Repairing a poor ground

• Correcting an incorrect glow plug installation

Does P0673 Require Replacing All Glow Plugs?

Not necessarily.

If testing confirms that only cylinder 3 has a failed glow plug, replacing all glow plugs may not be necessary.

However, if the glow plugs are old and several are showing signs of deterioration, replacing them as a set may be considered according to the manufacturer's recommendations.

Should the Glow Plug Be Tested Before Replacement?

Yes.

The complete circuit should be tested before replacing components.

The diagnosis should distinguish between:

Failed cylinder 3 glow plug

and

Fault in the cylinder 3 glow plug circuit

A new glow plug will not repair a broken wire, damaged connector, or faulty control module.

Common Diagnostic Mistakes

Replacing the glow plug without checking the wiring

A broken circuit will remain faulty after installing a new glow plug.

Replacing all glow plugs immediately

P0673 specifically identifies cylinder 3.

Using the wrong glow plug

The replacement must match the engine's electrical and physical specifications.

Ignoring the connector

A loose or corroded terminal can create excessive resistance.

Relying only on resistance

Some modern glow plug systems require current or waveform testing for a complete diagnosis.

P0673 vs. Other Cylinder Glow Plug Codes

The primary difference is the cylinder identified by the code.

P0671 → Cylinder 1 Glow Plug Circuit

P0672 → Cylinder 2 Glow Plug Circuit

P0673 → Cylinder 3 Glow Plug Circuit

P0674 → Cylinder 4 Glow Plug Circuit

P0675 → Cylinder 5 Glow Plug Circuit

P0676 → Cylinder 6 Glow Plug Circuit

P0677 → Cylinder 7 Glow Plug Circuit

P0678 → Cylinder 8 Glow Plug Circuit

P0679 → Cylinder 9 Glow Plug Circuit

P0680 → Cylinder 10 Glow Plug Circuit

P0681 → Cylinder 11 Glow Plug Circuit

P0682 → Cylinder 12 Glow Plug Circuit

The diagnostic principle is similar for each cylinder-specific glow plug code.

How Do You Clear P0673?

The correct process is:

Scan the vehicle → Record all DTCs → Inspect cylinder 3 glow plug → Test resistance/current → Inspect connector → Check wiring → Check fuse → Verify control-module power and ground → Test control output → Repair the confirmed fault → Clear DTCs → Perform a cold-start test → Rescan

If P0673 returns, the cylinder 3 glow plug circuit still has an unresolved problem.

Final Thoughts on P0673

P0673 – Cylinder 3 Glow Plug Circuit indicates an electrical problem involving the glow plug circuit for cylinder 3.

Possible causes include a failed glow plug, damaged wiring, loose or corroded connector, excessive circuit resistance, faulty glow plug relay or control module, blown fuse, or poor electrical connection.

The important point is that P0673 does not automatically mean the glow plug itself has failed. The complete circuit should be tested before replacing components.

The most effective diagnostic sequence is:

Test the cylinder 3 glow plug → Inspect the connector → Check wiring → Check fuse and power supply → Verify ground → Test the control signal → Evaluate the glow plug control module.

If the vehicle has hard cold starting, white smoke, rough idle, or increased cranking time, the glow plug circuit should be repaired before colder weather makes the symptoms more severe.