P0673 — Cylinder 3 Glow Plug Circuit/Open

The diagnostic trouble code P0673 indicates an issue with the glow plug circuit for cylinder 3. Specifically, it signals that the engine control unit (ECU) has detected an electrical open or fault in the wiring or component associated with the glow plug for that cylinder. This code is common in diesel engines where glow plugs are essential for starting and running efficiently.

Note: Labels for this trouble code may vary between manufacturers. Some OEMs may assign different alphanumeric codes or slightly different descriptions, but the core issue remains consistent.

Fast Facts:

System affected: Glow plug circuit

Severity: Moderate

Main symptoms: Rough starting, increased emissions, engine warning light

Driveability: Limited / No (depending on the severity)

Manufacturer variations for trouble code P0673

Different vehicle manufacturers may label or code this fault differently, though the underlying problem remains similar. Here are some known variations:

Volkswagen / Audi / Skoda / Seat: P0673 — « Cylinder 3 Glow Plug Circuit — Open »
Ford: P0673 — « Glow Plug Control Circuit — Cylinder 3 »
Mercedes-Benz: P0673 may also appear as « Glow Plug Module Circuit Open, Cylinder 3 »
BMW: Variations may include codes related to glow plug relay faults or circuit open conditions.

What does trouble code P0673 mean?

This code signifies that the ECU has detected an electrical problem—specifically an open circuit—within the glow plug circuit for cylinder 3. Glow plugs are vital components in diesel engines, used to preheat the combustion chambers to facilitate starting, especially in cold conditions. The ECU continuously monitors the electrical circuit that supplies power to each glow plug, and when it detects an abnormality—such as an open circuit—it triggers this fault code.

The circuit is considered « open » when there’s a break in the wiring or a failure in the glow plug itself, preventing current from flowing properly. This can mean the glow plug isn’t functioning correctly, or that a wiring connector or relay has failed. Typically, this code appears during cold starts or when the engine controller tests glow plug circuits as part of diagnostic routines.

Severity and risks of trouble code P0673

The presence of P0673 indicates a moderate issue. While it may not directly affect the engine’s immediate operation, it can lead to some notable problems. The main risks include difficulty starting the engine, especially in cold weather, increased emissions due to incomplete combustion, and potentially uneven engine running. Over time, ignoring this fault could lead to further damage or degradation of related components.

Does this problem prevent the vehicle from being driven? Limited / No. In many cases, the vehicle can be driven short distances, but it may be difficult to start in cold conditions or experience rough engine operation. Persistent issues should be diagnosed and repaired promptly to avoid further complications.

Symptoms of trouble code P0673

When this fault is present, drivers may notice several signs indicating a glow plug-related issue. Common symptoms include:

Hard starting or extended cranking times: The engine may struggle to start, especially in cold weather.
Rough engine running during initial warm-up: The engine may run unevenly or with decreased smoothness upon cold start.
Engine warning light or glow plug indicator illuminated: The dashboard may display a warning related to engine management or glow plug system.
Increased exhaust emissions: Due to incomplete combustion stemming from faulty glow plugs.
Potentially, reduced fuel economy: Caused by inefficient combustion process.

Most likely causes of trouble code P0673

This code generally stems from electrical or component faults in the glow plug circuit for cylinder 3. While specific causes may vary, the most common are listed here:

Faulty glow plug for cylinder 3: The glow plug itself may have failed internally, preventing proper heating or electrical connection.
Broken or damaged wiring or connector: The wiring harness or connector associated with theglow plug circuit could be open, frayed, or corroded, disrupting the electrical flow.
Blown fuse or relay for glow plugs: The fuse or relay controlling the glow plug circuit may have failed, cutting power to the glow plug.
Faulty glow plug control module or ECU wiring issues: Malfunctions in the control module or wiring harnesses may cause incorrect or incomplete signals.

How to diagnose trouble code P0673

Diagnosing this fault involves systematic checks to confirm the source of the issue. Here are the typical steps:

Visual inspection: Check the wiring and connectors linked to cylinder 3’s glow plug. Look for signs of damage, corrosion, or disconnection.
Check fuse and relay: Verify that the glow plug fuse and relay are intact and functioning. Replace if necessary.
Test the glow plug: Using a multimeter, measure the resistance of the glow plug; consult manufacturer’s specifications to determine if it’s within range.
Test electrical continuity: Check wiring continuity from the ECU to the glow plug, ensuring there are no breaks or high resistance.
Use live data to monitor circuit: Connect an OBD-II scanner capable of live data reading. Observe the relay operation and glow plug circuit status during vehicle startup.
ECU diagnostics: If physical checks are OK, scan for additional fault codes and perform tests on the ECU control modules according to manufacturer procedures.

Possible repairs for trouble code P0673

The repair process depends on the identified root cause. Here are common fixes, ranging from simple to complex:

Replace the faulty glow plug: This is a basic repair, requiring removal and installation of the suspect glow plug. Best performed by a professional or experienced technician.
Repair or replace damaged wiring or connector: Cleaning, repairing, or replacing compromised wiring or connectors restores proper circuit continuity. Usually a DIY task for experienced amateurs or professional technicians.
Replace blown fuse or faulty relay: Fuses are straightforward to replace; relays might require accessory installation or replacement from the OEM parts.
Check and repair control module wiring or ECU issues: This advanced repair involves diagnostic troubleshooting and possibly reprogramming or replacing control modules, best handled by professionals.

Vehicles commonly associated with trouble code P0673 in Europe

While ability to specify exact models varies due to limited data, diesel-powered vehicles from major manufacturers are predominantly affected. Typical affected brands include:

Volkswagen Group: Volkswagen, Audi, Skoda, Seat

Ford: Ford diesel models such as Transit, Focus, or Ranger

Mercedes-Benz: Diesel models with glow plug systems

BMW: Diesel engines with integrated glow plug circuits

Frequent mistakes with trouble code P0673

Diagnosing and repairing this fault can be challenging if common mistakes are made. Awareness of these pitfalls can save time and money:

Assuming the glow plug is always the issue: Ignoring wiring or relay problems can lead to incorrect repairs.
Not checking fuses and relays first: Often, a blown fuse or failed relay is the root cause and easy to fix.
Failing to perform live data monitoring: Relying solely on visual inspection may overlook circuit operation issues under actual load conditions.
Replacing parts without proper testing: Installing a new glow plug without confirming it’s defective can waste resources.

Quick FAQ — trouble code P0673

Can this code disappear on its own? Usually not. If the circuit or component fault persists, the code will return after clearing.

Can I keep driving? In many cases, limited driving is possible, but frequent starting problems and rough engine operation are warning signs to seek professional assistance.

Why does the code return after clearing? Because the underlying fault remains unresolved, whether it’s a wiring issue, faulty glow plug, or relay. The ECU detects the fault again during subsequent tests.