Technical Description of OBD-II Trouble Code
The glow plug circuit for Cylinder #3 is experiencing high voltage.
What does that mean?
This generic powertrain diagnostic trouble code (DTC) is commonly found in many OBD-II vehicles, including Jeep, Chrysler, BMW, Toyota, Volkswagen, Dodge, Ram, Ford, Chevrolet, Mazda, etc.
When code P066F is triggered, it indicates that the powertrain control module (PCM) has detected a high voltage situation in the glow plug control circuit for Cylinder #3. To determine the location of this cylinder in your specific year, make, model, and engine configuration, consult a reliable vehicle service resource.
Diesel engines rely on high compression instead of spark to initiate piston movement. To achieve maximum compression, the temperature in the cylinder must be increased. Glow plugs are used in each cylinder to accomplish this.
Glow plugs, which are often mistaken for spark plugs, are threaded into the cylinder head. The glow plug element is supplied with battery voltage through a glow plug timer or the PCM. When voltage is correctly applied, the glow plug becomes red hot and helps increase the cylinder temperature. Once the desired temperature is reached, the control unit restricts the voltage and the glow plug returns to its normal state.
If the PCM detects a higher than expected voltage in the glow plug control circuit for Cylinder #3, it will store code P066F and may illuminate the malfunction indicator lamp (MIL).
Example photo of a glow plug:
What is the severity of this DTC?
Any code related to glow plugs is likely to cause drivability issues. It is important to address a stored code P066F promptly.
What are some of the symptoms of the code?
Symptoms of a P066F trouble code may include:
What are some of the common causes of the code?
Possible causes for this code may include:
What are some P066F troubleshooting steps?
To accurately diagnose a code P066F, you will need a diagnostic scanner, a reliable source of vehicle information, and a digital volt/ohmmeter (DVOM). Use the vehicle information source to search for applicable technical service bulletins (TSB) that match your vehicle make, model, symptoms, and the stored code.
You may also need to obtain additional information such as 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 is necessary for a correct diagnosis of the stored code P066F.
After visually inspecting all glow plugs and glow plug control wiring and connectors, connect the diagnostic scanner to the vehicle diagnostic port. Retrieve all stored codes and freeze frame data, and record them for future reference. Test drive the vehicle to see if the code P066F is reset. Continue with the diagnosis if the code is reset, or if it is not, monitor for intermittent conditions that may worsen for a more accurate diagnosis.
A reliable way to test glow plugs is to remove them and apply battery voltage. If the glow plug glows bright red, it is functioning properly. If the glow plug fails to heat up, you can use a DVOM to test it for resistance and determine if it meets the manufacturer’s specifications. Take caution to avoid burns or starting a fire during this test.
If the glow plugs appear to be working correctly, use the scanner to activate the glow plug timer and test for battery voltage (and a ground) at the glow plug connector using the DVOM. If no voltage is present, test the power supply for the glow plug timer or glow plug controller. Test all related fuses and relays as recommended by the manufacturer. It is best to test system fuses and fusible links with the circuit loaded to avoid diagnostic errors.
If all fuses and relays are functional, use the DVOM to test the output voltage at the glow plug timer or PCM. If voltage is detected at the glow plug timer or PCM, there may be an open or shorted circuit. You can investigate the cause of the discrepancy or simply replace the circuit.
