P0674 — Cylinder 4 Glow Plug Circuit/Open

The diagnostic trouble code P0674 indicates an issue within the glow plug circuit for **cylinder 4** in your vehicle. In simple terms, this code means that the engine’s control system has detected a problem with the electrical supply or operation of the glow plug that preheats the cylinder during cold starts. Note that the specific labels used for this code can vary between different vehicle manufacturers, so it’s always good to verify according to your vehicle’s documentation.

Manufacturer variations for trouble code P0674

The label or code for this fault can vary slightly depending on the vehicle’s manufacturer. While many OEMs (Original Equipment Manufacturers) assign the generic P0674 code, some may have specific designations or additional diagnostic identifiers. It’s important to consult the specific service information for the vehicle in question, but here are some common variations:

• Volkswagen / Audi: P0674 (or sometimes detailed as ** »Cylinder 4 Glow Plug Circuit/Open »** with manufacturer-specific subcodes)
• Volkswagen Group (VAG): 02074
• Ford: P0674 (or related codes referencing glow plug circuit issues for cylinder 4)
• BMW: Sometimes as part of a group of codes like 11A5x, but usually related to glow plug circuit faults.
• Mercedes-Benz: Similar codes may appear with different labels referencing glow plug circuit faults.

What does trouble code P0674 mean?

The P0674 code is generated when the engine control unit (ECU) detects an abnormality in the electrical circuit that powers the glow plug for **cylinder 4**. This circuit includes the glow plug itself, wiring, connectors, and the relay or power supply controlling it.

During cold starts, glow plugs preheat the combustion chamber to ensure smooth starting and reduced emissions. The ECU constantly monitors the circuit resistance or voltage levels supplied to the glow plug. If there’s an open circuit — meaning the circuit is broken or not conducting electricity properly — the ECU flags this fault, resulting in the P0674 code.

This issue may be triggered by a faulty glow plug, damaged wiring, poor connections, or a defective relay. The code typically appears during cold weather, after multiple cold starts, or if the glow plug system is underperforming.

Severity and risks of trouble code P0674

The **severity** of the P0674 code depends on its cause and the vehicle’s overall condition. If the glow plug for cylinder 4 **is not functioning** correctly, the most immediate risk is difficulty starting the engine in cold weather — which can lead to longer cranking times or incomplete combustion. In some cases, it may cause misfires or increased emissions.

Driving with this code does not typically pose an immediate safety risk but can affect emissions and engine performance. Continuous driving with a faulty glow plug circuit may lead to further damage, such as damaged wiring or more critical issues in the ignition system.

**Conclusion**: Limited — the vehicle can often be driven, but repairs should be scheduled promptly to avoid potential damage or poor engine performance.

Symptoms of trouble code P0674

The presence of P0674 often correlates with specific engine behavior, especially during cold starts. Drivers might notice the following symptoms:

• Difficulties starting the engine in cold weather or after the vehicle has been sitting for some time.
• Rough engine idle during initial warm-up.
• Engine hesitation or stumbling when accelerating early in the drive cycle.
• Increased emissions or a visible check engine light (CEL) illuminated on the dashboard.
• Potential for limp mode activation in severe cases, limiting engine power to protect the system.

Most likely causes of trouble code P0674

As with many diagnostic trouble codes, the causes of P0674 are often interconnected. The most common origins include:

Note: Diagnosing this issue often involves checking the glow plug circuit hardware, wiring, and related control modules.

1. Faulty glow plug for cylinder 4: The glow plug itself may be burned out, damaged, or not functioning properly.
2. Broken or damaged wiring: The electrical wiring that supplies power to the glow plug might be cut, frayed, or corroded.
3. Corroded or poor electrical connection: Connectors or terminals in the circuit may have corrosion, dirt, or loose contacts.
4. Defective glow plug relay or control module: The relay responsible for switching power to the glow plug may have failed or be faulty.
5. OE-specific circuit issues: In some cases, a software or sensor malfunction linked to the engine control system.

How to diagnose trouble code P0674

To accurately identify the root cause of P0674, a systematic diagnostic approach is necessary. Here are generic steps to guide the process:

1. Visual inspection: Check the wiring harness, connectors, and relay associated with the glow plug circuit for damage, corrosion, or disconnection.
2. Inspect the glow plug: Remove the glow plug for cylinder 4 and test its resistance with a multimeter. A significantly different reading from the manufacturer’s specifications indicates a faulty plug.
3. Check power supply and ground: Perform voltage checks at the glow plug connector with the ignition on to see if power is reaching the glow plug circuit.
4. Test the relay: Swap or test the glow plug relay for correct operation, using a relay tester or by observing relay operation during engine start.
5. Use live data: Connect an OBD-II scanner to monitor real-time data and see if the ECU is commanding the glow plug for cylinder 4 and whether voltage levels are appropriate.
6. Check wiring continuity: Use a multimeter to verify wiring continuity from the relay to the glow plug, ensuring no opens in circuits.

Possible repairs for trouble code P0674

If the diagnostic steps confirm a fault, the repairs can vary from simple to more complex interventions. The following are typical repairs linked to this code:

• Replacing the glow plug: Usually a basic repair, but may require some engine disassembly depending on location. Best performed by a professional if access is difficult.
• Repairing wiring or connector issues: Fixing or replacing damaged wiring or connectors is generally straightforward but critical for ensuring proper electrical flow. A professional may be needed for complex wiring harness repairs.
• Replacing the glow plug relay: A quick swap in most cases, and a common repair for relay-related issues. Requires basic hand tools and electrical safety precautions.
• Inspecting and fixing control modules or sensors: If the issue stems from a faulty control module, it may require reprogramming or replacement, typically handled by a professional.

Vehicles commonly associated with trouble code P0674 in Europe

This fault code appears in a variety of European vehicles, especially those equipped with diesel engines and advanced glow plug systems. Some of the most affected brands include:

• Volkswagen Group: Volkswagen, Audi, Škoda, and SEAT
• Ford Europe
• BMW
• Mercedes-Benz

Within these brands, specific engine families susceptible to glow plug circuit issues include common rail diesel engines, which rely heavily on glow plug efficiency for cold start operation.

Frequent mistakes with trouble code P0674

Misdiagnosing or rushing repairs can lead to ineffective solutions. Some typical mistakes include:

• Replacing the glow plug without testing the circuit: This may not solve the actual problem if the wiring or relay is at fault.
• Ignoring connection corrosion or damage: Overlooking simple wiring issues can cause recurring faults.
• Failing to perform a comprehensive inspection: Not checking the relay, wiring continuity, and power supply can result in incomplete diagnosis.
• Replacing parts based solely on the code: Always verify component faults before replacement to avoid unnecessary repairs.

FAQ — trouble code P0674

Can this code disappear on its own?
No. If the fault persists, the code will typically remain until it is diagnosed and repaired. Temporary issues such as a loose connection may clear if fixed, but ongoing problems require intervention.

Can I keep driving?
In many cases, driving is possible, but it’s not recommended for long durations if the glow plug circuit is faulty. Cold starts may be difficult, and continued driving can worsen the issue or trigger other faults.

Why does the code return after clearing?
If the underlying fault (wiring, relay, or glow plug) is not addressed, the ECU will detect the issue again once the vehicle is restarted, leading the code to reappear.