Technical Description of OBD-II Trouble Code
The performance of the Glow Plug Circuit in Cylinder 12 is outside the expected range.
What does that mean?
This is a standard diagnostic trouble code (DTC) for powertrain issues in OBD-II vehicles. It can apply to various vehicle makes and models such as Ford, Toyota, Dodge, Ram, Chevy, GMC, VW Audi, Peugeot, Citroen, etc. The specific repair steps may vary depending on the year, make, model, and powertrain configuration.
When the code P06C4 is stored, it indicates that the powertrain control module (PCM) has detected an inconsistency in the glow plug control circuit for cylinder #12. To determine the location of the #12 cylinder for your specific vehicle, consult a reliable source of vehicle information.
Diesel engines rely on high compression instead of spark to initiate piston movement. To achieve maximum compression, the temperature in the cylinder needs to be increased. Glow plugs are used in each cylinder to accomplish this temperature increase.
Glow plugs, often mistaken for spark plugs, are threaded into the cylinder head for each individual cylinder. The glow plug element receives 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 voltage level outside the expected range for the glow plug control circuit in cylinder #12, it will store the code P06C4 and may illuminate the malfunction indicator lamp (MIL).
Photo of a typical 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 P06C4 promptly.
What are some of the symptoms of the code?
Symptoms of a P06C4 trouble code may include:
What are some of the common causes of the code?
Possible causes for this P06C4 fuel injector code may include:
What are some P06C4 troubleshooting steps?
To accurately diagnose a code P06C4, 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 relevant technical service bulletins (TSB) that match your vehicle make, model, exhibited symptoms, and stored code.
You may also need to access diagnostic flow charts, wiring diagrams, connector face views, connector pinout 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 P06C4.
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. Next, test drive the vehicle to see if the code P06C4 is reset. Continue driving until either the PCM enters readiness mode or the code is reset. If the code is reset, proceed with the diagnosis. If not, you may be dealing with an intermittent condition that may need to worsen before an accurate diagnosis can be made.
Here is a tip that the service manual does not provide. 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 your DVOM to test it for resistance. It is important to be cautious and avoid burns or starting a fire while performing 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 (use 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 advisable to test system fuses and fusible links with the circuit loaded, as a fuse for an unloaded circuit may appear functional when it is not.
If all fuses and relays appear to be functional, use the DVOM to test the output voltage at the glow plug timer or PCM (wherever it originates). If voltage is detected at the glow plug timer or PCM, suspect an open or shorted circuit. You can investigate the cause of the discrepancy or simply replace the circuit.
