P0672 — Cylinder 2 Glow Plug Circuit/Open #

The description of this code may vary depending on the vehicle manufacturer.

Known description variations:

• Cylinder 2 Glow Plug Circuit/Open (Generic, most brands)
• Glow Plug/Heater Circuit “B” (Cylinder 2) Open (Ford, GM)
• Pre-Heating Plug Circuit Malfunction, Cylinder 2 (Renault)
• Glow Plug #2 Control Circuit/Open (Mercedes-Benz)

Overview of Code P0672 #

Code P0672 is an OBD-II diagnostic trouble code indicating an issue within the glow plug circuit for cylinder 2. Glow plugs are heating elements used in diesel engines to preheat the combustion chamber, aiding cold starts. This code triggers when the Engine Control Module (ECM) detects an open circuit or abnormal resistance in the wiring or the glow plug itself for cylinder 2. The ECM continuously monitors the glow plug circuits to ensure they function as designed. When a fault is detected, the Check Engine Light will illuminate, and the code is stored in the vehicle’s memory.

Common Symptoms for Code P0672 #

When P0672 is present, the engine may exhibit several noticeable symptoms, especially during cold weather. Because the glow plug’s main job is to help the engine start and run smoothly when cold, issues in this circuit can make the engine hard to start or cause rough running until warmed up. You might also notice the engine warning light on your dashboard.

Typical symptoms include:

• Hard starting, especially in cold temperatures
• Rough idle after cold starts
• Increased white exhaust smoke during cold starts
• Decreased engine performance until the engine warms up
• Illuminated Check Engine or Glow Plug indicator light

Most Probable Causes for Code P0672 #

The P0672 code is most often triggered by issues within the glow plug circuit, with some causes being more common than others. Understanding the frequency of these causes can help prioritize your diagnostic approach.

The most frequent causes are:

1. Failed glow plug in cylinder 2 — The heating element itself may be burned out or have high resistance.
2. Faulty glow plug wiring or connector — Corrosion, loose connections, or damaged wiring can interrupt the circuit.
3. Defective glow plug relay or control module — The relay or control unit may fail to deliver power to the plug.
4. ECM (Engine Control Module) malfunction — Rare, but possible if internal circuitry monitoring the glow plug fails.

Step-by-Step Diagnostic for Code P0672 #

Diagnosing P0672 requires a methodical approach to avoid unnecessary parts replacement. Each step helps isolate the root cause, ensuring accurate and efficient repairs.

Recommended diagnostic steps:

1. Scan for other codes: Check for related glow plug or ECM codes that could indicate a broader issue.
2. Visual inspection: Examine the glow plug, wiring, and connector at cylinder 2 for visible damage, corrosion, or loose connections.
3. Measure glow plug resistance: Use a digital multimeter to measure the resistance of the cylinder 2 glow plug. Compare with manufacturer specs (typically 0.5–2 ohms).
4. Test wiring continuity: With the ignition off, check continuity between the glow plug connector and the relay/control module; repair any open circuits.
5. Check relay and power supply: Verify the glow plug relay supplies voltage to cylinder 2 during glow cycle. Replace relay if it fails to operate.
6. Verify ECM output: If all else checks out, confirm the ECM is commanding the glow plug circuit as intended (may require advanced diagnostic equipment).

Possible Repairs for Code P0672 #

Once the root cause is identified, targeted repairs can restore glow plug function. Most repairs are straightforward and can be completed with basic tools, but always follow OEM (Original Equipment Manufacturer) procedures.

Common repairs tied to each cause:

• Replace glow plug #2: If resistance is out of spec or the plug is open circuit.
• Repair or replace wiring/connector: Address any corrosion, damaged wires, or loose connections in the cylinder 2 glow plug circuit.
• Replace glow plug relay or control module: If it is not supplying power as required.
• Repair/replace ECM: In rare cases, if the ECM output is faulty (professional confirmation required).

Is It Safe to Drive With Code P0672? #

Limited — You can generally drive with code P0672, but it is not recommended to ignore it, especially if you live in a cold climate. Without a functioning glow plug on cylinder 2, your diesel engine may be hard to start in low temperatures and could run roughly or produce excess smoke until warmed up. While this code is not likely to cause immediate engine damage or a breakdown, prolonged operation without repair can strain the starter and battery, and may lead to higher emissions.

Vehicles Most Commonly Affected by Code P0672 #

This code is frequently found on a wide range of diesel-powered vehicles, especially those using individual glow plug circuits for each cylinder. It’s particularly common on models from manufacturers who equip their engines with OBD-II compliant diagnostics.

Vehicles often reporting P0672:

• Ford Super Duty (F-250, F-350) diesel models
• Chevrolet Silverado and GMC Sierra Duramax diesels
• Volkswagen TDI engines (various models)
• Mercedes-Benz Sprinter diesel vans
• Dodge Ram Cummins diesels
• Renault and Nissan diesel variants (Europe/Africa)

Common Mistakes & Best Practices for Code P0672 #

Misdiagnosis or hasty repairs often lead to wasted time and money. Understanding common pitfalls and following best practices ensures a successful fix.

Frequent errors and expert tips:

• Replacing all glow plugs without testing — Always measure resistance and test each plug individually.
• Neglecting the wiring — Wiring faults and corroded connectors are common, especially in older vehicles or harsh climates.
• Ignoring system voltage — Low battery voltage can mimic glow plug faults; ensure the battery and charging system are healthy.
• Not clearing codes after repairs — Always clear codes after repairs and verify the fault does not return on a cold start.
• Skipping OEM diagnostic procedures — Manufacturer-specific steps (e.g., special tests with scan tools) may be necessary for accurate diagnosis.

Quick FAQ for Code P0672 #

If you still have questions about this code, you’re not alone. Here are answers to the most frequent concerns:

Q: Can a single faulty glow plug cause hard starting?
A: Yes, especially in cold weather. Even one failed glow plug can make starting difficult and cause rough running until the engine warms up.

Q: Do I need to replace all glow plugs if one fails?
A: Not necessarily. Only replace the faulty plug unless others are close to the end of their service life or have similar wear.

Q: Will clearing the code fix the problem?
A: No. Clearing the code without fixing the underlying issue will only temporarily turn off the warning light. The code will return upon the next cold start cycle.

Q: Can I test glow plugs at home?
A: Yes. With basic tools like a digital multimeter, you can measure resistance and compare to OEM specifications.

Addressing P0672 promptly ensures your diesel engine remains reliable, especially when temperatures drop. If in doubt, don’t hesitate to consult a qualified technician or refer to your vehicle’s OEM service information.