Error Code P06C8 is defined as Cylinder 4 Glow Plug Incorrect. This is a generic trouble code, meaning it applies to all vehicles equipped with the OBD-II system, especially those made since 1996 up to present. This includes vehicle models from but not limited to Audi, Chevrolet, Ford, GMC, Ram, Volkswagen, etc. Anecdotally, this code is particularly common among Volkswagen vehicles. Specifications on the definition, troubleshooting, and repairs, of course, vary from one make and model, and powertrain configuration.
Diesel engines come equipped with glow plugs in each cylinder to increase the cylinder temperature to maximize compression. This is because it needs high compression rather than a spark plug to initiate the movement of the piston.
Glow plugs (often confused with spark plugs) are placed in each cylinder, threaded to the cylinder head. A battery voltage is applied to the glow plug element (through plug timer, also known as glow plug controller, or glow plug module) and the PCM. If a correct voltage is applied, the glow plug will literally glow red hot to increase the cylinder temperature. Once the cylinder temperature reaches the desired temperature level, the control unit will then restrict voltage, allowing the glow plug to return to its normal state.
When Error Code P06C8 is stored, this means the PCM (powertrain control module, also known as ECM or engine control module in other vehicle makes) has detected an incorrect degree of resistance in the glow plug circuit for cylinder number 4. Check with the source of reliable vehicle information to pinpoint the location of cylinder number 4 for the year, make, model, and powertrain configuration of the vehicle.
- Engine drivability issues
- Increased fuel consumption
- Delayed engine start-up
- Excessive black smoke coming from the exhaust
- Damaged glow plug(s)
- Loose or faulty glow plug connector
- Open or shorted glow plug circuit
- Defective glow plug timer
How to Check
Checking this code requires a DVOM (digital volt ohmmeter), dependable vehicle information for TSB (technical service bulletin) that has the code stored, vehicle (year, make, model, engine), and exhibited symptoms. Finding the right TSB can lead you to more easy and successful diagnostic and repair procedure.
You may also need the diagnostic flow chart for the code, including the connector face views, wiring diagram, connector pinout charts, component locations, and component test procedure/specifications from the vehicle information source. You will need all this information for proper diagnosis of the vehicle.
Start your diagnosis by inspecting all glow plugs and glow plug control connectors and wirings. Then, connect the diagnostic scanner to the vehicle diagnostic port. Retrieve all stored codes and freeze frame data, then record it for later.
Next, take the vehicle for a test drive to see if the code comes back. Drive until one of two things happens: either the PCM enters readiness mode, or the code resets. If the code does the latter, then continue with the diagnosis. If it does NOT, then you’re having an intermittent condition, which means you may have to wait for the problem to worsen before you can accurately diagnose it.
One good way to test the glow plug is to remove them and apply battery voltage. If the glow plug glows bright red, then it’s in good condition. If the glow plug fails to glow, that means it’s not heating up. You may want to take time and test it using DVOM. Most likely, you will find out it doesn’t meet the specifications set by the manufacturer. Be careful in doing this test, as the glow plug can be extremely hot.
If the glow plug seems to be working correctly, then use a scanner to activate the glow plug timer and test for battery voltage (make sure to test ground as well) at the glow plug connector (use DVOM. If there’s no voltage present, then 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’s best to test the system fuses and fusible links with the circuit loaded. The fuse for a circuit that is not loaded may appear functional, when it’s actually not, leading you to a wrong path of diagnosis.
If the fuses and relays seem to be in good shape, then test the output voltage at glow plug timer or PCM (wherever it comes from) using a DVOM. If you’re able to detect a voltage at the glow plug timer or PCM, then you can suspect an open or shorted circuit. You can search for the cause of the discrepancy, or simply replace the circuit.
How to Fix
Common repairs for this code include:
- Replacement of glow plug
- Repair or replacement of open or shorted glow plug control circuit
- Repair or replacement of loose or faulty glow plug connector
- Replacement of glow plug timer
Diagnosing the wrong cylinder is pretty common, and can be a huge headache. Thus, save yourself from trouble and make sure you’re addressing the right cylinder before starting your diagnosis.