P0673 — Cylinder 3 Glow Plug Circuit/Open #

Note: The wording of this Diagnostic Trouble Code (DTC) may differ depending on the vehicle manufacturer.

• Glow Plug Circuit Open – Cylinder 3 (Ford, GM, Chrysler, Toyota, Nissan, and most OEMs)
• Cylinder 3 Glow Plug Circuit Fault (Mercedes-Benz, BMW, Volkswagen)
• Cylinder 3 Preheater Circuit Malfunction (Peugeot, Renault, Citroën)

Summary of DTC P0673 #

The P0673 code indicates an electrical fault in the glow plug circuit for cylinder 3. A glow plug is a heating device used in diesel engines to preheat the air in the combustion chamber for easier starting, especially in cold conditions. The Engine Control Module (ECM) or Powertrain Control Module (PCM) monitors the electrical circuit to each cylinder’s glow plug and will trigger P0673 if it detects an open circuit or abnormal resistance in cylinder 3’s glow plug wiring. This code is specific to diesel engines and is commonly associated with starting issues and increased emissions when present. Prompt diagnosis ensures reliable cold starts and helps prevent further engine complications.

Common Symptoms for DTC P0673 #

When code P0673 is set, your vehicle may exhibit a variety of symptoms, some more noticeable than others. In many cases, you might find your engine struggles to start on cold mornings, or it may run rough until it warms up. The check engine light (CEL) will almost always illuminate, serving as a warning that something in the glow plug circuit isn’t operating as it should. If left unaddressed, other symptoms can develop, especially in colder environments where glow plugs play a critical role in starting diesel engines.

• Hard starting or extended cranking during cold weather
• Rough idle immediately after a cold start
• Noticeable white smoke from the exhaust on startup
• Check Engine Light illuminated
• Slight decrease in fuel efficiency (in rare cases)

Likely Causes for DTC P0673 #

The most common causes of P0673 typically relate to the electrical path between the ECM/PCM and cylinder 3’s glow plug. These can range from a failed glow plug itself to wiring issues or even a malfunctioning glow plug control module. Identifying the precise cause requires methodical testing, but some causes are more common than others:

1. Faulty cylinder 3 glow plug (open circuit or excessive resistance)
2. Defective glow plug relay or control module
3. Damaged, corroded, or disconnected wiring/connectors in the cylinder 3 glow plug circuit
4. ECM/PCM malfunction (rare)
5. Issues in the power supply or ground circuit for glow plugs

Step-by-Step Diagnostic for P0673 #

Diagnosing P0673 requires a logical, stepwise approach to isolate the fault without replacing parts unnecessarily. Always start by referencing your OEM (Original Equipment Manufacturer) wiring diagrams and repair procedures for your specific vehicle. Here is a recommended diagnostic path:

1. Verify the presence of code P0673 using a quality OBD-II scan tool.
2. Clear the code and perform a cold start to see if the code returns.
3. Visually inspect the glow plug wiring and connectors for cylinder 3 for signs of damage, corrosion, or loose connections.
4. Test the resistance of glow plug #3 using a multimeter (compare with manufacturer specs and other glow plugs).
5. Check for voltage at cylinder 3’s glow plug connector when the system is activated (cold engine, key ON).
6. Inspect the glow plug control module or relay for proper operation and output.
7. Test the wiring continuity between the ECM/PCM, glow plug relay/module, and glow plug #3.
8. If all else checks out, consider ECM/PCM diagnostic or consult OEM technical resources.

Possible Repairs for P0673 #

Once you’ve determined the root cause, repairs should focus directly on the failed component or circuit issue. Always use OEM or high-quality replacement parts to ensure durability and performance. Here are the most common repairs corresponding to the causes:

• Replace faulty glow plug #3
• Repair or replace damaged wiring or connectors at cylinder 3 glow plug
• Replace defective glow plug relay or control module
• Clean or repair corroded connections in the glow plug circuit
• In rare cases, replace or reprogram the ECM/PCM

Is It Safe to Drive with Code P0673? #

Driving with code P0673 is generally possible, but not recommended for extended periods, especially in cold climates. While the vehicle may still run, the affected cylinder will take longer to reach optimal combustion temperature, which can result in hard starting, increased white smoke, and higher emissions. In mild or warm weather, the impact might be minimal, but in colder temperatures, repeated hard starts can lead to battery strain, excessive fuel in the exhaust, or even damage to the diesel particulate filter (DPF) over time. Fixing the underlying issue promptly will help maintain reliable cold starts, efficient engine performance, and emissions compliance.

Vehicles Most Commonly Affected by P0673 #

While P0673 is a generic OBD-II code present on most diesel vehicles, certain models and engine families are more prone to glow plug circuit faults due to their wiring design or glow plug longevity. If you drive one of the following, it’s especially important to be proactive:

• Ford Super Duty Series (Powerstroke 6.0L, 6.4L, 6.7L)
• Chevrolet/GMC Silverado/Sierra (Duramax 6.6L)
• Dodge/Ram trucks (Cummins 5.9L, 6.7L)
• Volkswagen TDI diesel models
• BMW 3-Series and 5-Series diesel variants
• Mercedes-Benz E-Class and Sprinter vans (BlueTEC diesels)
• Nissan Titan XD (Cummins diesel)
• Toyota Hilux, Land Cruiser (diesel)

Frequent Mistakes & Best Practices for P0673 #

Misdiagnosis of P0673 is common, especially when skipping steps or failing to check simple issues like wiring condition. Following a disciplined process saves time, money, and frustration, ensuring you address the real problem rather than just the symptom.

• Do not replace all glow plugs without testing each one—often, only one is faulty.
• Always check for corroded or broken wiring before replacing components.
• Compare resistance readings across all glow plugs to spot anomalies.
• Use only OEM or reputable aftermarket glow plugs and relays—cheap parts often fail early.
• If in doubt, consult the vehicle’s OEM service manual for specific test values and wiring diagrams.

Quick FAQ for DTC P0673 #

Below are some fast answers to the most common questions drivers and technicians have when encountering P0673:

• Q: Will a failed glow plug damage my engine?
  A: Not immediately, but repeated hard starts can lead to excess fuel entering the exhaust, which may damage emissions components over time.
• Q: Can I just ignore the code if the engine starts fine?
  A: Ignoring it may be less problematic in warm weather, but it will likely cause trouble as temperatures drop and can increase emissions, potentially causing your vehicle to fail inspection.
• Q: Is this a DIY repair?
  A: Replacing a glow plug or fixing wiring is often within the reach of a skilled DIYer with the right tools; however, diagnosis should be methodical to avoid replacing unnecessary parts.