P066D Cylinder #2 Glow Plug Circuit High
OBD-II Trouble Code Technical Description
Cylinder #2 Glow Plug Circuit High
What does that mean?
This generic powertrain diagnostic trouble code (DTC) typically applies to many OBD-II vehicles. That may include but is not limited to vehicles from Jeep, Chrysler, BMW, Toyota, Volkswagen, Dodge, Ram, Ford, Chevrolet, Mazda, etc.
When a code P066D is set, it means that the powertrain control module (PCM) has detected a high voltage situation within the glow plug control circuit for cylinder #2. Consult a reliable vehicle service resource to determine the location of said cylinder in the code description for your particular year, make, model, and engine configuration.
Diesel engines use high compression instead of spark to initiate piston movement. Since there is no spark involved, cylinder temperature must be increased to maximize compression. Glow plugs are used in each cylinder to accomplish this increase.
Often confused with spark plugs, a glow plug for each individual cylinder is threaded into the cylinder head. Battery voltage is applied to the glow plug element via a glow plug timer (sometimes called a glow plug controller or glow plug module) and/or the PCM. When voltage is correctly applied to the glow plug, it will literally glow red hot and aid in increasing cylinder temperature. Once cylinder temperature reaches the desired level, voltage is restricted by the control unit and the glow plug returns to its normal state.
If the PCM detects a level of voltage for the cylinder #2 glow plug control circuit that is higher than expected, a code P066D will be stored and a malfunction indicator lamp (MIL) may be illuminated.
Example photo of a glow plug:
What is the severity of this DTC?
Any glow plug related code will likely be accompanied by drivability issues. A stored code P066D should be addressed with urgency.
What are some of the symptoms of the code?
Symptoms of a P066D trouble code may include:
Excessive black smoke from exhaust Engine drivability issues Delayed engine start up Reduced fuel efficiency Engine misfire codes may be storedWhat are some of the common causes of the code?
Causes for this code may include:
Bad glow plug/s Open or shorted glow plug control circuit Loose or faulty glow plug connector Defective glow plug timerWhat are some P066D troubleshooting steps?
A diagnostic scanner, a reliable source of vehicle information, and a digital volt/ohmmeter (DVOM) will be required in order to arrive at an accurate diagnosis of a code P066D. Use the vehicle information source to search for applicable technical service bulletins (TSB). If you locate a TSB that matches the vehicle make and model, symptoms exhibited, and the code stored, it will help you to arrive at a diagnosis.
You may also need to obtain diagnostic flow charts, wiring diagrams, connector face views, connector pin out charts, component locations, and component testing procedures/specifications from the vehicle information source. All this information will be needed to correctly diagnose the stored code P066D.
After performing a careful visual inspection of all glow plug and glow plug control wiring and connectors, connect the diagnostic scanner to the vehicle diagnostic port. Now, retrieve all stored codes and freeze frame data and record it for later (just in case you need it). Next, I would test drive the vehicle to see if the code P066D is reset. Drive until one of two things happens: Either the PCM enters readiness mode or the code is reset. If the code is reset, continue with the diagnosis. If it is not, you are dealing with an intermittent condition which may have to worsen before an accurate diagnosis may be achieved.
Here is a tip that the service manual will not give you. A sure way to test glow plugs is to re
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