P0672 is a generic OBD-II diagnostic trouble code indicating the powertrain control module detected a fault in the glow plug control circuit for cylinder 2 in a diesel engine.
This code identifies an electrical circuit condition rather than confirming a single failed component. The underlying cause requires targeted electrical diagnosis to identify the root cause.
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Key Takeaways
- P0672 indicates the control module detected an electrical fault in the glow plug circuit for cylinder 2 on a diesel engine.
- Possible causes include a failed cylinder 2 glow plug, damaged wiring, corroded connectors, or a faulty glow plug control module.
- Diagnosis requires inspecting the circuit wiring, testing the glow plug resistance, and verifying the control module operation.
- Repairs depend on the confirmed root cause and may involve replacing the glow plug, repairing wiring, or replacing the control module.
P0672 Code Description and Implications
P0672 indicates that the Powertrain Control Module (PCM) or Glow Plug Control Module has detected an electrical fault in the control circuit for the cylinder 2 glow plug.
Diesel engines rely on glow plugs to heat the combustion chambers, ensuring reliable cold starts and reducing initial emissions.
The control module monitors the voltage and current flow through the glow plug circuit to verify proper operation.
When the module detects an open circuit, a short to ground, a short to voltage, or an out-of-range resistance value, it logs the P0672 code.
Because P0672 is a generic code, this fundamental electrical monitoring logic applies across various diesel vehicles from multiple manufacturers.
However, the exact circuit architecture, module location, and diagnostic troubleshooting steps vary considerably depending on the specific vehicle application.
When diagnosing problem codes related to diesel starting systems, generic diagnostic paths cannot account for manufacturer-specific module topologies.
Common Causes of the P0672 Code
The underlying causes for a glow plug circuit code generally involve the glow plug itself, the control wiring, or the module.
Failed Cylinder 2 Glow Plug: The internal heating element inside the glow plug may burn out or fail open, preventing current from flowing through the circuit.
Wiring and Connector Issues: Damaged wiring, chafed insulation, or corroded connectors in the control circuit between the module and the cylinder 2 glow plug can interrupt the signal.
Faulty Glow Plug Control Module or Relay: The module or relay responsible for supplying power to the glow plugs may fail internally, preventing the circuit from energizing.
Poor Ground Connections: A corroded or loose chassis ground for the glow plug circuit can prevent proper current flow.
Symptoms Associated With P0672
The prominent symptom is the illumination of the Check Engine Light and often a flashing glow plug warning indicator on the dashboard.
The engine may crank normally but experience extended cranking times or fail to start, particularly in cold weather.
Drivers may notice a rough idle, misfires, or excessive white and gray exhaust smoke immediately after a cold start.
Depending on the application, the vehicle may enter a limp mode or disable certain emissions-related functions until the fault is resolved.
Diagnosing the P0672 Trouble Code
Diagnosis must begin by confirming the exact factory service information and wiring diagrams for the vehicle’s specific diesel engine.
Start by visually inspecting the wiring harness and connectors at the cylinder 2 glow plug for physical damage, heat exposure, or corrosion.
Use a digital multimeter to test the resistance of the cylinder 2 glow plug and compare it to the manufacturer’s specifications and the other cylinders.
Verify the continuity of the control circuit between the glow plug connector and the control module or relay.
Use a scan tool capable of commanding the glow plug system to monitor live data and verify module operation.
If the external wiring and glow plug resistance test correctly, the fault may lie within the glow plug control module itself.
Repairing the P0672 Issue
Repairs must follow confirmed diagnosis. Never replace engine starting components solely based on the presence of the code without verifying circuit integrity.
If external wiring damage or connector corrosion is found, repair the harness and secure the connections before re-evaluating the system.
If electrical testing confirms the cylinder 2 glow plug has failed its resistance test, replace the glow plug using the correct removal procedures to prevent breakage.
If the glow plug control module or relay fails testing, replace the unit according to the manufacturer’s service procedures.
On some applications, replacing a single failed glow plug may prompt the recommendation to replace the entire set if they share similar age and wear.
Cost Considerations for P0672 Repairs
Repair costs vary considerably depending on the confirmed root cause and the specific vehicle application.
Replacing a single glow plug involves minimal parts costs, but labor can be substantial if the engine requires significant disassembly for access.
Replacing a glow plug control module involves moderate to high parts costs depending on the vehicle, plus additional labor and potential programming fees.
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Prevention Strategies for Future Occurrences
Preventing glow plug circuit codes requires attention to the vehicle’s electrical system and starting environment.
Maintaining a healthy battery and charging system ensures the glow plug control module receives adequate voltage to operate the heating elements correctly.
Addressing engine oil leaks or coolant leaks promptly prevents fluid contamination that can degrade the glow plug connectors and wiring over time.
Using high-quality diesel fuel and appropriate cold-weather additives helps reduce the extreme thermal cycling load placed on the glow plugs during winter starts.
Troubleshooting Tips and Best Practices
Always check for Technical Service Bulletins related to P0672 for your specific vehicle application.
Manufacturers may release updated glow plug part numbers, revised wiring harness repair kits, or software updates for the glow plug control module to address known failure patterns.
Do not assume the glow plug has failed simply because a circuit code is present.
A simple broken wire, a corroded connector pin, or a failed relay can produce the P0672 code without the glow plug itself being defective.
Exercise extreme caution when removing glow plugs from aluminum cylinder heads, as seized or carbon-locked plugs can easily snap off and require extensive engine teardowns to extract.
More OBD-II Codes
| P0657 | P0660 | P0661 | P0670 |
| P0673 | P0674 | P0675 | P0676 |
| P0677 | P0678 | P0683 | P0685 |
| P0301 | P0302 | P0303 | P0300 |
| P0171 | P0174 | P0420 | P0430 |
| P0001 | P0100 | P0500 | P0700 |
Frequently Asked Questions
Is the P0672 code generic or manufacturer-specific?
P0672 is a generic SAE-defined OBD-II code. Its fundamental definition regarding a fault in the cylinder 2 glow plug circuit applies across various diesel manufacturers, though exact diagnostic steps vary.
Can a bad battery cause a P0672 code?
A weak battery typically causes low-voltage system codes rather than a specific cylinder glow plug circuit code. However, severe voltage drops can cause the control module to misread circuit resistance, though this is less common.
Will disconnecting the battery clear the P0672 code?
Disconnecting the battery may temporarily clear the code, but it does not repair the underlying electrical fault. It also erases valuable freeze frame data and resets readiness monitors, complicating professional diagnosis.
Can I drive my diesel vehicle with a P0672 code?
Driving short distances in warm weather is usually possible, but cold-weather starting will be severely compromised. Extended driving is not recommended, as unburned fuel from misfires can contaminate the engine oil and damage the diesel particulate filter.
Does P0672 mean the cylinder 2 glow plug must be replaced?
Not necessarily. While a failed internal heating element is a common cause, damaged wiring, corroded connectors, or a faulty glow plug control module can also interrupt the circuit. The wiring and module must be tested before replacing the glow plug.
What Should You Do About the P0672 Code?
Confirm the exact factory definition and diagnostic procedure for your specific vehicle application before attempting repairs.
Do not assume the cylinder 2 glow plug requires replacement based solely on the presence of the diagnostic trouble code.
Inspect the external wiring and connectors, verify the glow plug circuit resistance, and review live data to rule out external electrical faults.
Follow the applicable manufacturer diagnostic workflow to isolate the relevant system and components before replacing any hardware.
