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Technical Description of OBD-II Trouble Code
Fault in the Circuit of the Glow Plug Control Module
What does that signify?
The OBD code P0670 is a generic code that applies to all brands of modern diesel engines, including Ford, Dodge, Chevrolet, GMC, and VW Volkswagen vehicles. To understand the importance of this code, its consequences, and symptoms, it is crucial to comprehend the underlying dynamics.
Unlike a traditional gasoline engine, a diesel engine does not rely on a compressed fuel mixture and an electrical ignition source to function. Diesel engines have much higher compression than gasoline engines.
This high compression causes the air in the cylinder to reach temperatures over 600 degrees, which is enough to ignite the diesel fuel. When the piston reaches the top dead center of the cylinder, high-pressure fuel sprays into the cylinder. It immediately ignites upon encountering the super-heated air, and the expanding gases drive the piston downward.
Glow Plug
Since a diesel engine requires super-heated air to ignite the fuel, a problem arises when the engine is cold. When starting a cold engine, it is challenging to super-heat the air when its heat quickly dissipates to the cold cylinder head.
The glow plug provides the solution. Installed in the cylinder head, the pencil-shaped plug heats up until it glows for up to ten seconds. This raises the temperature of the surrounding cylinder wall, allowing the compression heat to reach a sufficient level for ignition.
A typical diesel engine glow plug:
Glow Plug Circuit
The circuit is common in all diesel engines, except for the component used to time the glow plug operation. The vehicle will either have a glow plug control module or the PCM will handle this. If you don’t have a service manual, you can contact an auto parts store and inquire about the availability of a control module. If not, then the computer controls the timing.
Operating Principles
When the ignition is on, it supplies power to the glow plug relay. The computer or control module will provide a ground to activate the relay. The oil temperature sensor plays a crucial role in the decision-making process. When the computer detects a cold engine, it will either activate the control module or relay by providing the ground.
Once activated, the relay supplies power to the glow plugs for a duration determined by the computer or control module.
If the vehicle has a control module, its sole function is to provide a timed ground to the relay. It will have a fused power source, and the computer supplies the ground to turn it on.
Symptoms
The glow plug warning light will illuminate, and the engine will be slow to start in warm weather or fail to start in cold weather.
If the engine does start, there will be a noticeable knocking noise until the engine warms up to operating temperature. White smoke will be visible from the exhaust as the excess fuel from the hard start burns off. The engine will have a noticeable misfire until the cylinder head temperatures rise sufficiently to support complete combustion.
Glow plug warning lamp illuminated:
Potential Causes
The glow plugs have a life expectancy of 30,000 – 40,000 miles and may have reached the end of their useful life, requiring replacement. Poor injection timing can cause excessive wear on the glow plug. Additionally, a stuck glow plug relay or timer module can cause them to burn out faster than a flea can jump on a slow-moving dog.
Diagnostic Steps & Possible Solutions
Other Glow Plug related DTCs: P0380, P0381, P0382, P0383, P0384, P0671, P0672, P0673, P0674, P0675, P0676, P0677, P0678, P0679, P0680, P0681, P0682, P0683, P0684.
Professional Service
While we always recommend addressing this issue through mechanical means, if that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this option, please upload your ECU file to our portal.
