P0675 — Cylinder 5 Glow Plug Circuit/Open

The diagnostic trouble code P0675 indicates a problem within the glow plug circuit of cylinder 5 in a diesel engine. This code suggests that the Engine Control Unit (ECU) has detected an open circuit or a malfunction in the glow plug’s electrical pathway specific to cylinder 5. It’s important to understand that labels or code designations might vary across different vehicle manufacturers.

Manufacturer variations for trouble code P0675

While the standard OBD-II code P0675 is universally recognised, for specific vehicle manufacturers, the label or code may vary slightly or be integrated within manufacturer-specific fault codes. Common variations include:

• BMW: Often coded as Cyl. 5 Glow plug circuit open in BMW-specific fault logs, but P0675 remains a standard code used in generic diagnostics.
• Volkswagen / Audi: May use manufacturer-specific codes but typically interpret to the same fault under the universal P0675 label.
• Mercedes-Benz: Similar, with standardized diagnosis referencing P0675.
• Renault and Peugeot: May include specific letters or code extensions but usually map to the same issue.

What does trouble code P0675 mean?

The P0675 code pertains to a malfunction in the glow plug circuit for cylinder 5. The ECU, which acts like the vehicle’s brain, continuously monitors the glow plug systems for proper operation. If it detects an open circuit—which is akin to a broken or disconnected wire—or when the glow plug fails to activate properly, this fault code is triggered.

Glow plugs are vital in diesel engines, especially during cold starts, as they heat the combustion chamber to facilitate ignition. When the ECU registers an issue with the glow plug circuit specific to cylinder 5, it records this fault and often illuminates the dashboard warning light.

This fault typically occurs in the context of cold weather, after replacing the glow plugs, or if there has been an electrical fault such as damaged wiring or a faulty relay. It’s also common if the glow plug itself or its electrical connector has become defective or corroded.

Severity and risks of trouble code P0675

The P0675 fault can lead to notable engine starting problems, especially in colder conditions. If ignored, it might cause increased wear and tear on the glow plug system, or prolonged starting times which can impact vehicle reliability. In some cases, if the glow plug circuit remains open, the engine may misfire or run roughly during cold starts.

While not immediately dangerous, continuous driving with this fault can lead to poor engine performance, increased emissions, and potential damage to the glow plug relay or wiring. Generally, the vehicle can still be driven, but caution is advised, especially in low temperatures.

Symptoms of trouble code P0675

The presence of P0675 often manifests through specific symptoms, including:

• Difficulty starting the engine, especially in cold weather conditions
• Engine misfire or rough idle during warm-up phase
• Increased cranking time before engine starts
• Illumination of the engine warning light or glow plug warning light on the dashboard
• Potential increase in emissions due to incomplete combustion during cold start

Most likely causes of trouble code P0675

Understanding the potential reasons behind the P0675 fault helps streamline diagnosis and repairs. Although the actual cause can vary depending on the vehicle’s condition, the most common causes include:

1. Open or damaged wiring in the glow plug circuit for cylinder 5 — Often a result of wear, corrosion, or accidental damage to the wiring harness.
2. Faulty glow plug in cylinder 5 — The glow plug itself can be burnt out or physically broken, preventing proper heating.
3. Malfunctioning glow plug relay or control module — The relay responsible for powering the glow plugs may have failed or become unreliable.
4. Issues with the engine control module (ECU) — Rare, but possible if there’s an internal fault in the ECU’s wiring or programming.
5. Corroded or poor electrical connections at the glow plug connector — Making it impossible for the circuit to complete properly.

How to diagnose trouble code P0675

Diagnosing the P0675 involves a systematic approach to rule out each possible cause. Here are basic diagnostic steps:

1. Visual Inspection: Examine the wiring harness and connectors leading to cylinder 5’s glow plug. Look for signs of damage, corrosion, or loose connections.
2. Check the glow plug’s resistance: Use a multimeter to measure continuity and resistance across the glow plug’s terminals. Compare readings with manufacturer specifications.
3. Test the relay: Activate the glow plug relay and listen for a clicking sound. Measure voltage at the glow plug connector when the relay is active.
4. Inspect the wiring for continuity: Perform a continuity test for the circuit wiring between ECU and glow plug. Ensure no breaks or shorts.
5. Review live data: Use a diagnostic scanner to monitor the glow plug control circuit live data and confirm if the ECU signals are present.
6. ECU diagnostics: Check for any related faults in the vehicle’s wiring diagram or manufacturer-specific diagnostic procedures.

Possible repairs for trouble code P0675

Once the cause has been identified, repair strategies can be implemented. Common repairs include:

• Replacing the faulty glow plug — A straightforward task usually performed by a professional to ensure proper installation and functioning.
• Repairing or replacing damaged wiring or connectors — A basic repair that restores proper electrical contact.
• Replacing the glow plug relay or control module — Essential if the relay is defective or unresponsive.
• Cleaning or restoring electrical contacts and connectors — Improves circuit integrity and prevents future faults.
• ECU reprogramming or replacement — In rare cases of internal faults, handled by a professional, often at an authorised service centre.

Vehicles commonly associated with trouble code P0675 in Europe

This fault code appears across various vehicles equipped with diesel engines that utilise glow plug systems. In Europe, some models frequently associated include:

Note: The following list is based on common observations and doesn’t cover every vehicle model:

• Volkswagen Group — Models such as Golf, Passat, and Tiguan with diesel engines
• BMW — Diesel engines across various series, notably 3 Series and 5 Series
• Mercedes-Benz — Common in diesel models, especially E-Class and C-Class
• Renault and Peugeot — Many diesel models, particularly with common rail systems

Frequent mistakes with trouble code P0675

Common errors during diagnosis or repair can lead to misdiagnosis and unnecessary costs. Errors include:

• Replacing the glow plug without checking the wiring or relay — Often the cause is electrical rather than the glow plug itself.
• Overlooking the relay or control module — Substituting glow plugs alone, when the relay or wiring is defective.
• Ignoring visual signs of wiring damage or corrosion — Which may be the root cause of the fault.
• Using unverified or incompatible parts during repairs — Potentially leading to incomplete or temporary fixes.

Quick FAQ — trouble code P0675

Can this code disappear on its own? A temporary glitch or wiring issue may clear naturally if the problem resolves itself, but it is unlikely to be permanent without addressing the root cause.

Can I keep driving? Yes, but with caution. If the engine starts reliably and runs smoothly, you may continue driving—but be mindful that cold starts might be more difficult, and further damage is possible if the fault persists.

Why does the code return after clearing? The most common reason is an unresolved underlying issue, such as damaged wiring, a faulty glow plug, or a defective relay, that requires proper repair to resolve permanently.

By understanding and correctly diagnosing the P0675 fault, technicians and vehicle owners can take informed steps to restore proper engine function, ensuring reliable cold starts and efficient operation.