P0672 – Cylinder 2 Glow Plug Circuit

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit | Location: Cylinder 2

Definition source: SAE J2012/J2012DA (industry standard)

P0672 indicates the powertrain control system has detected a fault in the Cylinder 2 glow plug circuit. Glow plugs are part of the diesel cold-start assist system; when the circuit for one cylinder does not behave as expected electrically, the control module may set this code and illuminate a warning lamp. The exact monitor strategy, enabling conditions, and what the module considers a fault can vary by vehicle, so confirm cylinder numbering, connector views, and test specifications in the appropriate service information. Treat P0672 as an electrical circuit problem to be verified with inspection and targeted testing, not as a confirmed glow plug failure without measurements.

What Does P0672 Mean?

P0672 – Cylinder 2 Glow Plug Circuit means the control module detected an electrical fault associated specifically with the glow plug circuit for cylinder 2. Per SAE J2012, the DTC identifies the affected function (the cylinder 2 glow plug circuit) but does not, by itself, prove which component is defective. The fault can involve the glow plug element, its wiring and connectors, the power feed or ground path, or the driver circuitry that controls current to the glow plug. Diagnosis should focus on verifying circuit integrity and control operation for cylinder 2 compared with the other cylinders.

Quick Reference

  • Subsystem: Cylinder 2 glow plug control and its electrical circuit (feed, control, and ground paths).
  • Common triggers: Open circuit, high resistance, poor terminal contact, damaged harness, failed glow plug, or a control driver not switching as commanded.
  • Likely root-cause buckets: Wiring/connector issues, glow plug (actuator) fault, power/ground distribution problem, or control module/driver fault (varies by vehicle).
  • Severity: Usually higher impact during cold starts; may cause extended cranking, rough start, smoke, or a no-start in low temperatures.
  • First checks: Verify cylinder numbering, inspect harness/connectors at cylinder 2, check for corrosion/loose pins, and compare circuit behavior to other cylinders.
  • Common mistakes: Replacing the glow plug without confirming power/ground integrity or ignoring connector pin-fit and harness damage near heat/vibration points.

Theory of Operation

Glow plugs are resistive heating elements used to raise combustion-chamber temperature during cold starts. The control module (or a dedicated glow plug control unit, depending on vehicle design) energizes each glow plug via a driver stage and monitors circuit behavior to confirm the commanded heating event occurred. This may be done by measuring current flow, observing voltage change at the driver output, or using internal diagnostics that infer load presence.

If the cylinder 2 circuit does not respond as expected—such as an open, excessive resistance, poor connection, or a driver that cannot supply or control the load—the module records a fault for that cylinder’s glow plug circuit. Because designs vary, the circuit may be individually controlled per cylinder or managed through a shared supply with individual control/feedback paths.

Symptoms

  • Hard starting: Extended crank time, especially when ambient temperature is low.
  • Rough start: Uneven idle or misfire-like feel immediately after start that improves as the engine warms.
  • White smoke: Increased exhaust smoke during cold start due to incomplete combustion.
  • Warning lamp: Check engine or glow plug indicator illuminated (behavior varies by vehicle).
  • Reduced cold performance: Sluggish response or poor drivability for the first minutes after startup in cold conditions.
  • No-start (cold): In severe cases and low temperatures, the engine may fail to start until conditions improve.

Common Causes

  • Open circuit in the cylinder 2 glow plug feed wire between the control module/relay and the glow plug
  • High resistance in the cylinder 2 glow plug circuit due to corrosion, damaged insulation, or poor crimp/splice quality
  • Poor terminal fit, pushed-out pin, or connector damage at the cylinder 2 glow plug or at the harness connection (varies by vehicle)
  • Glow plug internal electrical fault (open or excessive resistance) on cylinder 2
  • Power supply issue to the glow plug control module/relay (blown fuse, weak feed, or overheated connection)
  • Ground path issue affecting the glow plug control module/relay or the glow plug return path (design varies by vehicle)
  • Glow plug control module/relay internal circuit fault for the cylinder 2 output (where individually controlled)
  • Harness routed too close to heat/sharp edges causing intermittent opens when the engine moves

Diagnosis Steps

Tools typically needed include a scan tool with data logging and bi-directional control (if supported), a multimeter, and back-probing leads. A wiring diagram and connector views for your exact vehicle are essential to identify the correct cylinder 2 circuit, power feeds, and grounds. If available, use a clamp meter for current checks and basic hand tools to access the glow plug and its connector safely.

  1. Confirm the code and capture freeze-frame: Scan all modules for DTCs, record freeze-frame data and any related glow plug, power supply, or module communication codes. Address power/ground or module-wide codes first if present.
  2. Verify cylinder numbering and access point: Use service information to confirm which physical cylinder is “2” and locate the glow plug, its connector, and the controlling module/relay path for that cylinder (varies by vehicle and engine layout).
  3. Clear and recheck with controlled conditions: Clear the DTC, then run a cold-start or commanded preheat cycle (as applicable) while monitoring for code return. If the scan tool supports it, command the glow plug output test and observe whether P0672 resets.
  4. Visual inspection of the cylinder 2 circuit: Inspect the cylinder 2 glow plug connector, wiring insulation, and routing. Look for heat damage, chafing, oil saturation, loose retention, corrosion, or a partially seated connector. Repair obvious wiring/connector issues before deeper testing.
  5. Wiggle test for intermittent opens: With the engine off and key on (or during an output test when safe), gently wiggle the harness near the glow plug, along the valve cover area, and near the module/relay connector while monitoring scan tool data and/or the test result. Any abrupt change indicates a connection or conductor fault.
  6. Check power feed integrity to the controller/relay: Using the wiring diagram, verify the controller/relay power supply circuit(s) and ground(s) are present and stable under load. Perform a voltage-drop test across the power feed and ground path while the glow system is commanded on; excessive drop indicates resistance in wiring, fuse links, or connections.
  7. Test the cylinder 2 glow plug resistance (component check): Disconnect the cylinder 2 glow plug connector and measure the glow plug’s resistance per service information. Compare to a known-good cylinder on the same engine if appropriate. An open or clearly out-of-family reading supports a faulty glow plug, but confirm the circuit can supply it before replacement decisions.
  8. Check circuit continuity end-to-end (open/high resistance): With the controller/relay connector unplugged and the glow plug connector unplugged, perform continuity testing for the cylinder 2 control/feed wire. Also test for unwanted continuity to ground or to other circuits that could indicate harness damage. If continuity is marginal, flex the harness while testing to reveal breaks.
  9. Load-test the circuit (find resistance that continuity misses): If wiring checks “good” on continuity but the fault persists, perform a loaded test of the cylinder 2 circuit. This can be done by commanding the output on (if supported) and measuring voltage at the glow plug connector, then performing voltage-drop testing between the controller output pin and the glow plug terminal to locate hidden resistance in connectors/splices.
  10. Compare cylinder outputs (if individually controlled): If the system controls cylinders individually, compare the cylinder 2 output behavior to another cylinder during the same command event using the scan tool and/or electrical measurements. A consistent deviation isolated to cylinder 2 points to that branch of wiring, the glow plug, or the specific driver channel.
  11. Evaluate the controller/relay after circuit verification: Only after verifying the glow plug and the cylinder 2 circuit (including power/ground quality under load), consider an internal fault in the glow plug controller/relay. Follow service information for any module-specific pinpoint tests and relearn/coding requirements (varies by vehicle).
  12. Verify the repair: After repairs, clear codes and run multiple preheat/cold-start cycles while logging relevant data. Confirm P0672 does not return and that any readiness/monitor status (where applicable) completes without re-faulting.

Professional tip: Don’t rely on continuity alone for glow plug circuit faults. A wire or terminal can show continuity with a multimeter yet fail under the higher current demand of a glow plug. Prioritize voltage-drop testing and a loaded check during a commanded preheat/output test to pinpoint resistance at connectors, splices, and fuse/relay junctions.

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Factory repair manual access for P0672

Check repair manual access

Possible Fixes & Repair Costs

Repair cost for P0672 can vary widely because the correct fix depends on what testing proves in the cylinder 2 glow plug circuit, along with access, labor time, and whether wiring repair or component replacement is required.

  • Repair wiring damage: Fix opens, chafing, melted insulation, or corrosion found in the cylinder 2 glow plug feed/return path; restore proper routing and protection.
  • Service connectors: Clean and dry terminals, correct poor pin fit, replace damaged locks/seals, and ensure the glow plug connector fully seats and retains.
  • Replace the cylinder 2 glow plug: Only after verifying the plug fails appropriate resistance/continuity testing compared to service information expectations.
  • Repair power/ground supply issues: Correct shared feed, ground, or fuse/relay problems that affect the glow plug circuit’s ability to carry current as designed (layout varies by vehicle).
  • Replace glow plug control hardware: If testing confirms the driver/control unit is not commanding or regulating the circuit correctly and all external wiring/loads check out.
  • Perform post-repair verification: Clear the DTC, run the appropriate monitor/cold-start enable conditions per service information, and confirm the code does not return.

Can I Still Drive With P0672?

You can often drive with P0672, but expect cold-start difficulty, rough running when cold, and increased emissions until the issue is repaired. If you have a no-start, repeated stalling, severe misfire-like behavior, or warning indicators that suggest reduced engine control, avoid driving and have the vehicle diagnosed to prevent further complications.

What Happens If You Ignore P0672?

Ignoring P0672 can lead to progressively worse cold-start performance, longer cranking, unstable idle during warm-up, and persistent warning lights. Ongoing starting strain and incomplete combustion during cold operation can contribute to increased smoke/emissions and may stress related starting and electrical components over time.

Compare nearby cylinder glow trouble codes with similar definitions, fault patterns, and diagnostic paths.

  • P0682 – Cylinder 12 Glow Plug Circuit
  • P0681 – Cylinder 11 Glow Plug Circuit
  • P0680 – Cylinder 10 Glow Plug Circuit
  • P0679 – Cylinder 9 Glow Plug Circuit
  • P0678 – Cylinder 8 Glow Plug Circuit
  • P0677 – Cylinder 7 Glow Plug Circuit

Key Takeaways

  • P0672 is a circuit fault: It indicates a problem in the cylinder 2 glow plug circuit, not a confirmed mechanical failure by itself.
  • Wiring and connections come first: Opens, corrosion, and poor terminal fit are common and should be verified before replacing parts.
  • Test-driven diagnosis matters: Confirm power/ground integrity and the glow plug’s electrical condition using service information procedures.
  • Symptoms are often cold-related: Problems typically show up most during cold starts and early warm-up.
  • Verify the repair: Clear the code and confirm the monitor runs and passes under the correct conditions.

Vehicles Commonly Affected by P0672

  • Diesel engines with glow plugs: Any platform using individual cylinder glow plugs can set this DTC.
  • High-mileage vehicles: Age-related harness brittleness and terminal fretting increase circuit-fault likelihood.
  • Cold-climate operation: Frequent cold starts increase glow plug usage and expose marginal circuits.
  • Vehicles with recent engine work: Disturbed connectors, pin damage, or misrouting near the cylinder head can trigger circuit issues.
  • Vehicles with oil/coolant contamination: Fluids in connector areas can promote corrosion and poor contact (source varies by vehicle).
  • Vehicles exposed to road salt/humidity: Environmental corrosion can affect terminals and grounds.
  • Applications with tight engine-bay packaging: Heat and abrasion near the head can degrade wiring insulation and connector housings.
  • Systems using a separate glow control module: Additional connectors and power feeds can create more potential circuit-fault points (design varies by vehicle).

FAQ

Does P0672 mean the cylinder 2 glow plug is bad?

No. P0672 indicates the cylinder 2 glow plug circuit is faulted. The glow plug can be the cause, but wiring damage, connector issues, power/ground problems, or a control driver fault can produce the same DTC. Testing is required to confirm the failed part.

Can a wiring issue alone trigger P0672?

Yes. An open circuit, corroded terminal, poor pin tension, or damaged insulation in the cylinder 2 glow plug circuit can prevent proper current flow or signal integrity and set P0672 even if the glow plug itself is electrically sound.

Will P0672 always cause a hard start?

Not always. Some engines may still start normally, especially in warmer conditions, but cold-start performance and warm-up smoothness may degrade. The exact symptom set varies by vehicle strategy and ambient temperature.

Should I replace all glow plugs if only P0672 is present?

Not automatically. Replace only what diagnosis confirms. It can be reasonable to inspect other glow plug circuits during the same service, but the correct approach is to test the cylinder 2 circuit and address verified faults rather than replacing parts preemptively.

What should I check first for P0672?

Start with a visual inspection of the cylinder 2 glow plug connector and the harness segment near the cylinder head for looseness, corrosion, heat damage, and chafing. Then confirm circuit integrity with appropriate electrical tests per service information before condemning the glow plug or control hardware.

After any repair, clear P0672 and confirm the glow plug monitor completes and passes under the correct enable conditions, since some vehicles require specific cold-start criteria before the circuit is rechecked.