The OBD (On-Board Diagnostics) code P0670 is a generic code that applies to many modern diesel engines, including those used in vehicles from brands like Ford, Dodge, Chevrolet, GMC, and Volkswagen. To understand its meaning and implications, it is essential to master the operation of diesel engines and their specificities.
Operation of a Diesel Engine
Unlike a gasoline engine, a diesel engine does not rely on a compressed fuel-air mixture and an ignition spark to operate. Thanks to high compression, the air in the cylinder reaches a temperature above 600°C, sufficient to ignite the fuel. When a diesel engine starts, fuel is injected into the cylinder at top dead center. This fuel ignites instantly, generating gas expansion that pushes the piston downward.
Role of Glow Plugs
Starting a cold diesel engine is problematic because the compression heat can be quickly dissipated by the cold cylinder head. Glow plugs are essential to solve this problem. These pencil-like components heat up to a glow within seconds, increasing the temperature of the cylinder walls to ensure efficient combustion.
The management of glow plugs varies by vehicle:
- Some use a specific control module.
- Others rely on the PCM (Powertrain Control Module).
Key Elements to Check
- Batteries: A full charge is essential to ensure rapid engine rotation and maintain compression heat.
- Glow Plug Relay: Located near the starter relay, this component handles high currents.
- Oil Temperature Sensor: This sensor tells the PCM when and how long to activate the glow plugs.
- Glow Plug Fuse: Supplies power to the relay to activate the glow plugs.
- Glow Plug Control Module or PCM: Determines the preheating duration based on temperature sensor information.
Symptoms of Code P0670
- Glow plug indicator light turns on.
- Hard starting in cold or hot weather.
- Knocking noise and white smoke from the exhaust.
- Misfires until the engine reaches its optimal temperature.
Potential Causes
- Worn glow plugs (lifespan: 30,000 to 40,000 miles).
- Faulty relay or module.
- Poor injection timing, leading to premature wear.
Diagnostic Steps and Solutions
- Check the Battery: Ensure it is fully charged.
- Inspect the Wiring: Identify any faults or damage.
- Test the Glow Plug Relay: Use a voltmeter to check the voltage at the main power terminal and detect any voltage drop (>0.5 V). Replace the relay if necessary.
- Analyze the Oil Temperature Sensor: Disconnect the sensor and test the relay by turning the key.
- Check the Glow Plugs: Use a test light or ohmmeter to verify their continuity. A resistance greater than 0.4 ohms indicates a problem.
Related Codes
Here are other DTC codes related to glow plugs: P0380, P0381, P0382, P0383, P0384, P0671 to P0684. These codes can provide additional clues about specific components to inspect.
By following these steps, you can diagnose and resolve issues associated with code P0670.