P0672 Code: Cylinder 2 Glow Plug Circuit/Open – Complete Diagnostic & Repair Guide
A comprehensive technical guide to diagnosing, troubleshooting, and fixing P0672 error code in diesel engines
Technical Overview
The P0672 trouble code indicates a malfunction in the glow plug circuit for cylinder 2 specifically. This diagnostic trouble code (DTC) is exclusive to diesel engines, where glow plugs serve as critical components for cold starting by preheating the combustion chamber to ensure proper ignition of diesel fuel.
How Glow Plug Systems Work
Diesel engines rely on compression ignition rather than spark ignition. In cold conditions, the compressed air may not reach the necessary temperature for ignition. Glow plugs solve this by:
- Preheating the combustion chamber before startup
- Maintaining heat during cold operation for reduced emissions
- Providing post-heating to stabilize combustion at idle
Symptoms & Warning Signs
When the P0672 code is stored in your vehicle’s PCM, you may experience one or more of the following symptoms, with varying degrees of severity:
| Symptom | Frequency | Severity | Conditions |
|---|---|---|---|
| Check Engine Light illuminated | Always | Medium | Immediately after fault detection |
| Hard starting in cold weather | Very Common | High | Ambient temperature below 50°F (10°C) |
| Extended cranking time | Common | Medium | All temperatures, worse in cold |
| Rough idle after startup | Common | Medium | First 1-2 minutes of operation |
| White smoke from exhaust | Occasional | Medium | Cold starts, unburned fuel |
| Reduced engine power | Rare | Low | With multiple glow plug failures |
| Poor fuel economy | Occasional | Low | Most noticeable in cold weather |
Root Causes & Underlying Issues
The P0672 code can be triggered by various electrical and mechanical issues in the glow plug system. Understanding the root cause is essential for proper repair:
Primary Causes (Most Common)
- Faulty glow plug in cylinder 2 – The heating element has failed internally (open circuit or shorted)
- Glow plug harness issues – Open circuit, short to ground, or short to power in the wiring to cylinder 2
- Faulty glow plug control module – The module cannot supply power to cylinder 2’s glow plug
Secondary Causes (Less Common)
- Poor electrical connections at the glow plug (corrosion, loose connector)
- PCM software issues requiring updates or reflashing
- Low system voltage affecting glow plug operation
- Physical damage to glow plug or wiring from previous repairs
Comprehensive Diagnostic Procedure
Follow these detailed steps to accurately diagnose the P0672 code. Always begin with the simplest checks before moving to more complex diagnostics:
-
Initial Scan & Code Verification
Use a professional-grade OBD-II scanner to confirm P0672 is present and check for any additional codes that might provide context. Note freeze frame data to understand the conditions when the code set.
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Visual Inspection
Thoroughly inspect the glow plug harness and connections for cylinder 2. Look for damaged insulation, corroded terminals, loose connections, or signs of overheating (melted plastic, discoloration).
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Resistance Testing
Disconnect the glow plug harness and measure the resistance of the glow plug for cylinder 2. Compare with manufacturer specifications (typically 0.1-6.0 ohms for most vehicles). Also test adjacent glow plugs for comparison.
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Voltage Supply Verification
With the engine cold and ignition on, check for proper voltage at the glow plug connector when the system is activated (should be close to battery voltage, typically 10.5V+). Use a test light or multimeter.
-
Current Draw Test
Using a clamp meter, measure the current draw of cylinder 2’s glow plug during activation and compare to known good cylinders. A significantly different reading indicates a faulty glow plug.
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Swap Test Method
If possible, swap the glow plug from cylinder 2 with another cylinder and see if the code follows the plug. This is a definitive test but requires more labor.
-
Control Module Output Test
Using an oscilloscope or advanced scanner, test the glow plug control module outputs to ensure it’s sending proper signals to all glow plugs, particularly cylinder 2.
Required Diagnostic Tools
Diagnostic Flowchart
| Test | Expected Result | If Incorrect |
|---|---|---|
| Glow Plug Resistance | 0.5 – 6.0 ohms (check spec) | Replace glow plug |
| Voltage at Connector | 10.5V+ during activation | Check wiring/control module |
| Current Draw | 10-20A during heating phase | Replace glow plug |
| Continuity to PCM | Less than 5 ohms resistance | Repair wiring harness |
| Swap Test | Code moves with glow plug | Replace glow plug |
Repair Procedures & Techniques
Based on your diagnostic findings, follow the appropriate repair procedure. These steps assume you’ve identified the root cause through proper diagnosis:
Procedure A: Replacing a Single Glow Plug
- Disconnect the negative battery terminal to prevent accidental activation
- Locate and remove any components obstructing access to the glow plugs
- Carefully disconnect the electrical connector from the faulty glow plug
- Use a dedicated glow plug socket and ratchet to remove the defective glow plug
- Inspect the glow plug hole for carbon buildup and clean if necessary
- Apply a small amount of anti-seize compound to the threads of the new glow plug
- Hand-thread the new glow plug to avoid cross-threading
- Torque the glow plug to manufacturer specifications (typically 10-20 Nm)
- Reconnect the electrical connector and any removed components
- Reconnect the battery, clear codes, and perform a system test
Procedure B: Repairing Glow Plug Wiring
- Disconnect the battery and identify the damaged section of wiring
- Cut out the damaged portion, leaving enough wire to work with
- Strip approximately 1/2 inch of insulation from both ends
- Use butt connectors or solder to join a new section of appropriate gauge wire
- Apply heat shrink tubing to protect the connection from moisture and corrosion
- Secure the repaired wiring away from heat sources and moving components
- Use wire loom or conduit for additional protection if needed
- Reconnect battery, test operation, and clear codes
Procedure C: Replacing Glow Plug Control Module
- Disconnect the battery and locate the glow plug control module
- Document or photograph the wiring connections before disassembly
- Disconnect all electrical connectors from the module
- Remove the mounting bolts and carefully remove the module
- Install the new module and secure with mounting bolts
- Reconnect all electrical connectors according to your documentation
- Reconnect battery and perform module initialization if required
- Clear codes and test all glow plugs for proper operation
Common Mistakes to Avoid
- Overtightening glow plugs (can damage threads or break the plug)
- Using incorrect anti-seize compound (can affect electrical conductivity)
- Not cleaning the glow plug hole before installation (can affect heat transfer)
- Forgetting to clear codes after repair (check engine light will remain on)
Repair Cost Analysis
Costs for repairing P0672 vary significantly based on your vehicle, location, and whether you perform the repair yourself or hire a professional:
DIY Single Plug
Parts only (one glow plug)
Skill Level: IntermediateProfessional Single
Parts + labor (1-1.5 hours)
Most common optionFull Set Replacement
All glow plugs + labor
Recommended approachControl Module
Module replacement + labor
If module is faultyDetailed Cost Breakdown by Vehicle Type
| Vehicle Type | Part Cost (Single) | Labor Cost | Total Estimate | Full Set Total |
|---|---|---|---|---|
| Passenger Car | $25 – $60 | $80 – $150 | $105 – $210 | $180 – $400 |
| Pickup Truck | $30 – $70 | $100 – $200 | $130 – $270 | $220 – $500 |
| SUV | $35 – $75 | $120 – $220 | $155 – $295 | $250 – $550 |
| Commercial Vehicle | $40 – $90 | $150 – $250 | $190 – $340 | $300 – $650 |
Prevention & Long-Term Maintenance
Proper maintenance can extend glow plug life and prevent future P0672 codes. Follow these guidelines for optimal system performance:
Proactive Maintenance Strategies
- Maintain Electrical System Health – Ensure your battery and alternator are in good condition to provide adequate voltage (at least 10.5V during glow plug activation)
- Use High-Quality Diesel Fuel – Premium diesel with proper cetane rating and additives reduces carbon buildup on glow plugs
- Proper Cold Starting Procedure – Allow glow plugs to complete their cycle (wait for glow plug light to turn off) before cranking in cold weather
- Address Engine Issues Promptly – Problems like low compression or injector issues can strain glow plugs and shorten their lifespan
- Follow Manufacturer Intervals – Replace glow plugs preventatively according to your vehicle’s maintenance schedule (typically 60,000-100,000 miles)
Glow Plug Life Expectancy by Type
| Glow Plug Type | Average Lifespan | Replacement Cost | Advantages |
|---|---|---|---|
| Standard Metal | 40,000 – 60,000 miles | $ | Low cost, widely available |
| Ceramic | 60,000 – 80,000 miles | $$ | Faster heating, more durable |
| Pressure Sensor | 80,000 – 100,000 miles | $$$ | Integrated diagnostics, precise control |
| Quick-Start | 70,000 – 90,000 miles | $$ | Reduced wait time, improved cold starts |
Frequently Asked Questions
In warmer conditions, you may be able to drive with a P0672 code, though you might experience slightly rough idle after startup. However, in cold weather (below 50°F/10°C), the vehicle may be difficult or impossible to start. It’s recommended to address the issue promptly to prevent potential damage to other glow plugs and avoid being stranded in cold weather.
While you can replace just the faulty glow plug, most professional technicians recommend replacing the entire set. Glow plugs typically wear at similar rates, so if one has failed, others are likely near the end of their service life. Replacing all plugs ensures even heating across cylinders and prevents having to repeat the repair labor for other cylinders soon after.
P0672 specifically indicates a problem with cylinder 2’s glow plug circuit. Similar codes for other cylinders include P0671 (cylinder 1), P0673 (cylinder 3), P0674 (cylinder 4), etc. The diagnostic approach is identical for all cylinder-specific codes, just applied to the specific cylinder mentioned in the code.
The P0672 code itself won’t directly damage your engine, but the underlying issue can contribute to problems over time. A faulty glow plug can cause incomplete combustion in that cylinder, leading to increased carbon deposits, fuel dilution of oil, and potential issues with the Diesel Particulate Filter (DPF) in modern vehicles. Extended cranking to start the engine can also place additional strain on the starter motor and battery.
Glow plug lifespan varies based on type, vehicle usage, and operating conditions. Standard metal glow plugs typically last 40,000-60,000 miles, while ceramic or advanced types can last 80,000-100,000 miles. Vehicles used primarily for short trips in cold climates may experience shorter glow plug life due to more frequent heating cycles.
