P0675 Cylinder 5 Glow Plug Circuit -- Comprehensive Diagnostic Guide

P0675 Cylinder 5 Glow Plug Circuit - Comprehensive Diagnostic Guide

Summary of the code

• Code and definition: P0675 corresponds to the Cylinder 5 Glow Plug/Heater Circuit. In open-source code references, it is described as the glow plug heater circuit for cylinder 5. This places P0675 squarely in the cylinder glow plug circuit family.
• Global context: P0675 is part of the OBD-II powertrain codes. OBD-II codes are diagnostic trouble codes generated by the vehicle's on-board systems to indicate issues with engine/drive train control and emissions-related components.
• Emissions/testing context: As a powertrain DTC, P0675 can trigger MIL (check engine light) and may be included in emissions-related diagnostic data when applicable.

What this means for diagnosis

• The fault indicates a problem in the control path of cylinder 5's glow plug/heater circuit. It implies either the glow plug itself is not heating properly, the wiring/connectors to the glow plug are faulty, or the PCM/driver for that circuit is not energizing the glow plug as commanded. It can be a simple faulty component or a symptom of a larger wiring/drive circuit issue.

Symptoms

• Hard starting or extended cranking, especially in cold ambient conditions.
• MIL illumination (Check Engine Light) with P0675 stored or pending.
• Rough idle or misfire indications in cylinder 5 environment when glow plug is not heating as expected (depending on engine design and whether glow assist is used).
• Possible poor cold-start performance, increased exhaust smoke during startup.
• In some vehicles, no obvious symptom aside from MIL and a DTC.

Probable Causes

• Glow plug 5 itself is open or high resistance (faulty element): ~35-50%
• Glow plug harness/wiring to cylinder 5 damaged or connector loose/corrosion: ~20-30%
• Glow plug relay or cylinder 5 driver circuit fault in PCM/ECU: ~10-20%
• Blown fuse or power supply issue to the glow plug circuit: ~5-10%
• PCM/ECU fault affecting the glow plug driver (less common): ~5%
• Other mechanical issues that affect starting but not glow plug heating (e.g., battery, cranking speed): variable, but usually ruled out early in testing

Recommended diagnostic flow (step-by-step, practical and repeatable)

1) Verify and document

• Use an OBD-II scanner to confirm P0675 is present and note any freeze-frame data, long-term fuel trim, and engine coolant temperature. Check for other cylinder-related DTCs (e.g., P0670-P0677 family) that might indicate a shared driver or multiple glow plugs.
• Record engine type (diesel vs. gasoline with glow plug assist) and ambient temperature, since cold-weather driving affects glow systems.

2) Visual inspection and quick checks

• Inspect the glow plug harness and wiring to cylinder 5 for abrasion, cuts, or damaged insulation; check connectors for corrosion or loose terminals.
• Inspect fuses and the glow-plug relay (if equipped): confirm they are intact and properly seated.
• Look for signs of PCM/ECU harness damage or moisture ingress near the engine bay.

3) Electrical checks to the glow plug circuit

• With the ignition on, perform a voltage check at the glow plug heater circuit for cylinder 5 to confirm supply voltage is present when commanded (via the PCM/relay).
• Check ground continuity for the glow plug circuit; ensure a solid ground path back to the battery negative/engine block ground.
• If serviceable, test the glow plug directly (resistance test) using an ohmmeter:
  • A healthy glow plug typically shows a low resistance (a few ohms, varies by design). Very high resistance or infinite resistance indicates an internal open circuit.
  • Note that some engines require the glow plug to be heated briefly while powered, so do not misinterpret a cold measured resistance as failure if the plug has not been energized yet.

4) Component-specific checks

• Glow plug itself: If cylinder 5 glow plug resistance is out of specification or there is an open circuit, replace the glow plug(s). In many engines, it is recommended to replace all glow plugs in the same bank or as per service guidelines to avoid mismatched heating characteristics.
• Wiring harness/connectors: Repair or replace damaged wiring or connectors. After replacement, test continuity and resistance again to confirm integrity.
• Glow plug relay/driver circuit: If voltage is present at the glow plug when commanded but the resistance is good, consider a relay fault or PCM driver issue. Swap or test with a known-good relay if applicable, or use an oscilloscope/functional test to observe the driver signal.
• Fuses and power supply: Confirm the fuse is intact and that there is proper power feed to the relay/driver circuit.

5) PCM/ECU and software considerations

• If all physical checks pass but the fault persists, consider a PCM/ECU driver issue. In some cases, software updates or reprogramming can resolve a stuck or non-energizing driver circuit. This is less common and typically a last resort after verifying all wiring, fuses, and functional test results.

6) Rule-out related conditions

• If multiple glow plug circuits (P0670-P0677) are set or frequently failing together, inspect the common driver path, relay, or power supply. A shared component or harness damage can produce multiple codes.

7) Post-repair verification

• Clear the DTCs and perform a cold-start cycle to verify that P0675 does not reappear.
• Perform a drive cycle that includes cold startup in typical operating conditions to confirm consistent glow plug operation and engine starting performance.
• Re-check for any new DTCs after a test drive.

Repair Actions

• Replace cylinder 5 glow plug if open or high resistance is detected.
• Repair or replace damaged wiring or connectors in the glow plug circuit.
• Replace the glow plug relay or fix the PCM driver circuit if the control signal is not energizing the glow plug.
• Replace a blown fuse or correct power supply issues to the glow plug circuit.
• If ECU/PCM driver faults are suspected and validated, consider software updates or a replacement/repair of the ECU as per manufacturer guidelines.

Safety Considerations

• Glow plug systems (especially in diesel engines) can carry high current during energizing. Disconnect battery before heavy electrical work; wear eye protection and insulated tools.
• When performing resistance checks, ensure the system is de-energized to avoid false readings or injury.
• Avoid shorting test leads to grounding points; use proper jigs or adapters and follow the vehicle's service manual procedures.
• Engine bays contain hot components; allow cooling if performing physical checks on glow plugs or wiring.

Documentation

• DTC: P0675 cylinder 5 glow plug circuit
• Symptoms observed (start condition, cold-weather behavior, MIL status)
• Tests performed (voltage checks, resistance measurements, continuity, relay swap)
• Parts replaced (glow plug(s), wiring harness, relay, fuse)
• Post-repair verification results (new start performance, absence of DTC, drive cycle results)

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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