The Eobd/obdii P0670 diagnostic trouble code signifies a problem within the glow plug control module circuit. This code is common across various diesel engine models, including Ford, Dodge, Chevrolet, GMC, and Volkswagen. Understanding this code is crucial for effective diagnosis and repair. This article will explain the function of the glow plug system, the implications of the P0670 code, common symptoms, and diagnostic steps.
How Diesel Engines and Glow Plugs Work
Unlike gasoline engines, diesel engines rely on compression ignition. The high compression within the cylinder generates enough heat to ignite the fuel. However, in cold temperatures, this heat dissipates quickly, making starting difficult. Glow plugs address this issue by preheating the combustion chamber. These pencil-shaped devices, located in the cylinder head, heat up and raise the cylinder wall temperature, enabling efficient combustion during cold starts.
A typical diesel engine glow plug
The Glow Plug Control System and the P0670 Code
The glow plug system consists of several components, including the glow plugs themselves, a glow plug relay, an oil temperature sensor, a fuse, and either a dedicated glow plug control module or the engine control unit (PCM). The P0670 code indicates a fault within the circuitry controlling these components. This could mean a problem with the module itself, the wiring, or a related component. The system typically operates as follows:
- Ignition On: Power is supplied to the glow plug relay.
- Cold Engine Detected: The oil temperature sensor informs the PCM or control module.
- Relay Activation: The PCM or module grounds the relay, activating it and supplying power to the glow plugs.
- Preheating: Glow plugs remain active for a predetermined time, based on engine temperature.
Symptoms of a P0670 Code
A P0670 code often manifests through the following symptoms:
- Illuminated Glow Plug Warning Light: Glow plug warning lamp illuminated
- Difficult or No Start (Especially in Cold Weather): The engine may crank but fail to start, or require extended cranking.
- Engine Knocking: A noticeable knocking sound might be present until the engine warms up.
- White Smoke from Exhaust: Unburnt fuel can cause white smoke during the initial start.
- Engine Misfire: One or more cylinders might misfire until the engine reaches operating temperature.
Diagnosing the P0670 Code
Troubleshooting the P0670 code involves a systematic approach:
- Battery Check: Ensure the battery is fully charged, as a weak battery can hinder starting and exacerbate glow plug issues.
- Wiring Inspection: Visually inspect all wiring and connectors associated with the glow plug system for damage, corrosion, or loose connections.
- Relay Testing: Use a voltmeter to check for voltage drop across the glow plug relay. A significant drop indicates a faulty relay. This is a common cause of the P0670 code.
- Power Supply Verification: Confirm power from the ignition switch to the relay with the key on.
- Relay Activation Test: Disconnect the oil temperature sensor and turn the key on. The relay should click. Jumpering the ground on the small relay terminal should activate the glow plugs.
- Glow Plug Testing: Test each glow plug for an open circuit using a test light or ohmmeter. They should show a good ground or very low resistance (less than 0.4 ohms).
Conclusion
The EOBD/OBDII P0670 code points to a fault in the glow plug control module circuit. Addressing this issue requires a thorough diagnostic process, starting with the most common culprits like the relay and progressing to more complex components. By following the steps outlined in this article, you can effectively pinpoint the source of the problem and restore your diesel engine to proper working order. Remember to consult your vehicle’s specific repair manual for detailed instructions and safety precautions.
