P0670 — Glow Plug Control Module Control Circuit/Open #

Note: The label for DTC P0670 may vary depending on the vehicle manufacturer.

• Glow Plug/Heater Module Control Circuit/Open (Ford, GM, Chrysler, Mercedes-Benz)
• Glow Plug Module Control Circuit Malfunction (Volkswagen, Audi)
• Pre-Glow Relay Circuit (Open Circuit) (Renault, Nissan)
• Glow Plug Controller Fault (Toyota, Isuzu)

Summary for code P0670 #

The P0670 DTC is triggered when the Engine Control Module (ECM) detects an issue within the glow plug control module control circuit. This component is responsible for managing the glow plugs, which are heating elements used to warm diesel engine cylinders for optimal cold starting. If the circuit is “open,” it means the current flow is interrupted or absent, often due to wiring or module faults. As a result, starting the engine in cold conditions can become difficult, and performance issues may appear. This code is specific to diesel engines and is a signal that immediate attention is required to avoid extended cold starts or further damage.

Common symptoms for P0670 #

Wondering how your vehicle might behave if it’s showing a P0670 code? The symptoms are often most noticeable during cold weather, when the engine relies on glow plugs to start smoothly. You may experience some or all of the following:

• Hard starting or no start in cold weather
• Rough idle immediately after cold start
• Excessive white smoke from the exhaust on startup
• Illuminated Check Engine Light (CEL) or Malfunction Indicator Lamp (MIL)
• Decreased engine performance until the engine warms up

Probable causes for P0670 (by frequency) #

What could be behind a P0670 code? The reasons range from simple electrical issues to component failure. Here’s what technicians typically find, ordered by likelihood:

1. Faulty glow plug control module (the relay or controller that manages power to the glow plugs)
2. Open or damaged wiring in the glow plug control circuit (including connectors and harnesses)
3. Corroded or loose electrical connections at the glow plug module or ECM
4. Failed ECM (rare, but possible if other causes are ruled out)
5. Blown fuse related to the glow plug system circuit

Step-by-step diagnosis for P0670 #

Diagnosing a P0670 code need not be daunting. Think of it like tracing a river upstream to find the source of a blockage. Here’s a systematic approach:

• 1. Scan for additional DTCs: Sometimes, related codes (like P0671, P0672, etc.) provide more clues.
• 2. Inspect fuses: Check all fuses related to the glow plug system for continuity and replace any that are blown.
• 3. Visual check: Look for obvious signs of damaged, corroded, or disconnected wiring and connectors going to the glow plug module.
• 4. Test the glow plug control module: Use a multimeter to check for power at the module and ground integrity.
• 5. Inspect wiring continuity: With the battery disconnected, check for continuity and open circuits in the wiring harness between the ECM and glow plug module.
• 6. Module bench test: If accessible, bench test the module or swap with a known good unit if possible.
• 7. Check ECM output: If all else checks out, verify the ECM is sending the command signal to the glow plug module.

Possible repairs for P0670 #

Resolving a P0670 code means restoring the circuit’s integrity and function. Each cause leads to a different repair, so here’s what you or your technician might do:

• Replace the glow plug control module if it’s found to be faulty
• Repair or replace damaged wiring and connectors in the glow plug circuit
• Clean or tighten corroded connectors and terminals
• Replace any blown fuses supplying the glow plug relay/module
• In rare cases, repair or replace the ECM after confirming all other components are functional

Is it safe to drive with code P0670? #

Limited. While the vehicle may still run, especially in warm conditions, driving with a P0670 code is not recommended in cold weather. The glow plug system is critical for cold starts—ignoring this code could leave you stranded on a cold morning or result in hard starts and rough running. Prolonged neglect may stress the starter, battery, and cause excessive smoke on startup. Address the issue as soon as possible.

Vehicles most affected by P0670 #

This DTC is most commonly found in diesel-powered vehicles, especially those using electronically controlled glow plug systems. While it can appear in any modern diesel, here are the makes and models where it is most frequently reported:

• Ford Super Duty (F-250, F-350, etc.) — Power Stroke engines
• Chevrolet Silverado/GMC Sierra — Duramax diesel
• Dodge Ram — Cummins diesel
• Volkswagen TDI models
• Mercedes-Benz Sprinter, E-Class diesel
• Isuzu NPR/NQR trucks
• Renault Master/Trafic diesel

Common mistakes & best practices for P0670 #

Misdiagnosing a P0670 can lead to unnecessary part replacements and wasted time. Here’s how to avoid the pitfalls:

• Replacing glow plugs instead of the control module — P0670 relates to the module/circuit, not the plugs themselves
• Ignoring wiring checks — Many problems stem from broken or corroded wires, not the module
• Overlooking fuse integrity — A simple blown fuse can trigger this code
• Not checking related codes — Additional glow plug codes can help pinpoint the problem cylinder or component
• Skipping connector inspection — Moisture and corrosion are common in diesel engine bays

Quick FAQ on P0670 #

Here are answers to some of the most common questions about this code:

• Can a faulty glow plug cause P0670?
  No, P0670 specifically indicates a control circuit/module issue, not an individual glow plug failure. Codes like P0671–P0678 relate to specific glow plug faults.
• Does clearing the code fix the problem?
  No, simply clearing the code will not resolve the underlying electrical or component fault. The code will likely return until the root cause is repaired.