1. What is P0670?

P0670 is the Diagnostic Trouble Code for a Glow Plug Control Module Circuit malfunction. In diesel vehicles, the Glow Plug Control Module (GPCM) regulates current to the glow plugs to ensure the combustion chamber reaches the temperature needed for reliable cold starts.

Why It Matters

When the control circuit fails, glow plugs may not heat correctly, resulting in long cranking times, white smoke at startup, poor cold-weather drivability, and increased emissions.

2. Potential Causes & Real-World Examples

P0670 is typically an electrical/control issue. Below are common root causes with real-world instances from field diagnostics:

• Glow Plug Control Module Failure — Example: 2015 Ford F-350 intermittently failed to preheat due to module internal relay burn; replacing the module resolved P0670.
• Corroded or Damaged Wiring — Example: 2016 Chevy Silverado showed open circuits where bundle chafed near battery terminals.
• Bad Relay or Blown Fuse — Example: 2017 Ram 2500 had a burnt relay contact that prevented current to glow plugs.
• Faulty Temperature Sensor / Feedback — Example: 2018 VW Amarok sent incorrect temp data so ECM disabled preheat, setting P0670.
• ECM ↔ GPCM Communication Fault — Example: Loose CAN/comm connector caused intermittent control drops and code logging.

3. Symptoms

Watch for these signs when P0670 appears:

• Hard starting or extended cranking in cold weather
• Thick white smoke on startup
• Rough idle immediately after starting
• Check Engine Light illuminated with P0670 stored
• Reduced low-temperature drivability and increased emissions

4. Vehicles Prone to P0670

P0670 is specific to diesel vehicles with glow plug preheating systems. Common models where P0670 is frequently reported:

• Ford Super Duty (Power Stroke diesel)
• Chevrolet / GMC Duramax trucks
• Dodge Ram (Cummins diesel)
• VW / Audi TDI platforms
• Mercedes-Benz Sprinter vans
• Isuzu & other light diesel pickups

Always confirm model-specific diagnostics—some manufacturers have known TSBs or updated modules for glow plug issues.

5. Diagnostic Flow

A methodical, top-down approach saves time. Use live data tools (like the iCarzone UR1000) and follow this flow:

Example: a Silverado with intermittent P0670 logged only under damp conditions — connector corrosion at the GPCM caused voltage drops and code logging. Cleaning and sealing the connector fixed it.

6. Solutions & Execution

• Replace Glow Plug Control Module: When internal relays/transistors fail.
• Repair Wiring & Connectors: Replace damaged sections, apply dielectric grease, and seal connectors against moisture.
• Replace Faulty Relay / Fuse: Use OEM-spec parts to avoid overcurrent issues.
• Replace Defective Glow Plugs: Replace as a set where practical and verify resistance specs.
• ECM Reflash / Replacement: If commands are missing or module firmware is known-buggy.

7. Repair Costs & Precautions

• GPCM Replacement: $150–$400
• Glow Plugs (set): $80–$200
• Relay / Fuse: $10–$60
• Wiring Repair: $50–$250
• ECM Replacement: $500–$1,500

Precautions

• Disconnect battery before servicing the glow plug circuit.
• Label connectors before unplugging to avoid misrouting.
• Always verify the root cause — replacing glow plugs alone may not fix control module faults.

8. Preventive Measures

• Inspect and clean glow plug wiring and connectors annually.
• Protect the GPCM from water ingress and road salt.
• Replace glow plugs as a maintenance item before they fail.
• Run periodic diagnostics with the iCarzone UR1000 to catch early anomalies.

9. FAQ

10. Summary

P0670 flags a glow plug control circuit issue that impairs diesel cold starts. Follow a methodical diagnosis: verify codes and live data (UR1000), inspect power/ground, test relays/fuses, check wiring/connectors, and only replace modules after confirming failure. Timely repair restores reliable starts and reduces emissions.