P0673 — Cylinder 3 Glow Plug Circuit

How do I diagnose P0673 myself?

Start with a scan: confirm P0673, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the diesel glow plug system, and verify the suspect component against live data before buying parts.

What does OBD2 code P0673 mean?

OBD2 code P0673 flags a problem with the diesel glow plug system (cylinder 3 glow plug circuit). The car is usually drivable while you plan the repair. Common culprits: corroded glow plug connectors, burned-out glow plug, blown fuse in the glow plug circuit.

What is the most common cause of P0673?

The most common causes are: corroded glow plug connectors, burned-out glow plug, blown fuse in the glow plug circuit.

Will P0673 clear itself?

Sometimes P0673 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How much does it cost to fix P0673?

Replace one glow plug — $80–$200; Replace the glow plug relay/module — $150–$450; Replace a full set of glow plugs — $250–$600. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Diesel engines need a little extra help starting in cold temperatures. Unlike gasoline engines that rely entirely on the spark from ignition plugs, diesel combustion chambers depend on glow plugs to preheat the cylinder before the fuel-air mixture can ignite. When the powertrain control module detects a fault in the cylinder 3 glow plug circuit, it logs trouble code P0673 and turns on the check engine light. This code belongs to the powertrain category under the OBD2 standard, meaning it relates directly to engine and transmission management systems.

The glow plug for cylinder 3 is a small resistive heating element threaded into the combustion chamber. During startup, the engine control unit energizes the glow plug circuit for a few seconds, bringing the tip of the plug to temperatures high enough to ignite diesel fuel even when the engine block is cold. The control module constantly monitors the electrical characteristics of each glow plug circuit. If it sees an open circuit, a short to ground or battery voltage, or resistance that falls outside the expected range, P0673 gets set. On inline diesel engines, cylinder numbering typically starts at the front pulley end. On V-configuration diesel engines, the numbering follows the manufacturer's firing order diagram, so you need to verify the exact location before you start pulling parts apart. Some cylinders sit deep in the engine valley or behind the intake manifold, which affects labor time and repair costs significantly.

One important point about P0673: the check engine light does not come on from a single bad reading. The control module must observe the fault condition repeat under specific operating conditions before it decides the problem is real and not just a momentary electrical hiccup. This is why the freeze frame data stored with the code is so valuable. That snapshot records engine load, RPM, coolant temperature, vehicle speed, and other sensor readings at the exact moment the fault was detected. Use those conditions as a target when you reproduce the problem during testing.

Common symptoms of P0673

• White smoke billowing from the tailpipe during cold starts, indicating unburned diesel fuel
• Difficulty starting the engine, especially when temperatures drop below freezing
• Glow plug warning light remains illuminated on the dashboard after startup
• Rough, uneven idle that smooths out once the engine reaches operating temperature
• Check Engine Light active on the instrument cluster

What causes P0673?

• Burned-out or internally open glow plug in cylinder 3
• Damaged wiring harness or loose electrical connector feeding the cylinder 3 glow plug
• Blown fuse protecting the glow plug circuit
• Faulty glow plug relay or glow plug control module
• Corroded or oxidized connectors at the glow plug terminal

How to diagnose P0673

1. Hook up an OBD2 scanner and confirm P0673 is stored in the ECU memory. Record the freeze frame data, which shows engine conditions when the fault triggered.
2. Check for any other diagnostic trouble codes present at the same time. Coexisting codes often point to the root cause, such as a charging system issue or module communication fault. Also search for manufacturer technical service bulletins that apply to your vehicle make, model, and model year.
3. Perform a visual inspection of all wiring and connectors in the glow plug circuit. Look for broken insulation, melted wires, corrosion buildup, or connectors that are not fully seated.
4. Using a digital multimeter, measure the resistance of the cylinder 3 glow plug directly at the terminal. A healthy glow plug typically reads between 0.5 and 2 ohms. Infinite resistance or an open circuit means the plug is dead.
5. Verify that battery voltage reaches the glow plug bus bar during the pre-glow phase using a test light or multimeter.
6. Clear the code, complete a full drive cycle that recreates the freeze frame conditions, and verify P0673 does not come back.

How to fix P0673

Work from the simplest and most probable causes toward the expensive components:

• Replace one glow plug (cylinder 3): $80–$200
• Replace the glow plug relay or control module: $150–$450
• Replace the complete glow plug set: $250–$600

How much does it cost to fix P0673?

The total bill varies depending on which part is actually faulty. Here are the typical scenarios at independent shop labor rates in USD:

• One cylinder 3 glow plug replacement: $80–$200
• Glow plug relay or module replacement: $150–$450
• Full glow plug set replacement: $250–$600

Most drivers end up spending somewhere between $80 and $600 to resolve P0673. The wide range reflects how different the underlying cause can be. Always confirm the diagnosis before buying parts. Swapping a relay when the problem is a single bad plug wastes money and diagnostic time.

Can you drive with P0673?

Once the engine is running and warmed up, driving with P0673 stored is generally safe. The real concern is cold weather. If you have multiple dead or failing glow plugs, the engine may struggle to start on a frigid morning or fail to start altogether. You can limp to work on a warm day, but do not wait until winter to address this code.

Related OBD2 codes

• P0600: Serial Communication Link Malfunction
• P0601: Internal Control Module Memory Check Sum Error
• P0602: Control Module Programming Error
• P0603: Internal Control Module Keep Alive Memory (KAM) Error
• P0604: Internal Control Module Random Access Memory (RAM) Error
• P0605: Internal Control Module Read Only Memory (ROM) Error