What Does It Mean?
This is a generic powertrain diagnostic trouble code (DTC) and generally applies to OBD-II vehicles. This may include, but is not limited to, vehicles from VW, Audi, Ford, GMC, Ram, Chevy, etc. Anecdotally, this code appears to be found primarily on Volkswagen/VW vehicles. Although generic, the exact repair steps may vary depending on the year, make, model, and powertrain configuration.
When a P06C5 code is stored, it means the Powertrain Control Module (PCM) has detected an incorrect degree of resistance in the glow plug circuit for cylinder #1. Consult a reliable vehicle information source to determine the location of cylinder #1 for your specific year/make/model/powertrain configuration.
Diesel engines use high compression instead of spark to initiate piston movement. Since no spark is involved, the cylinder temperature must be increased to maximize compression. Glow plugs are used in each cylinder to achieve this increase.
Often confused with spark plugs, a glow plug for each individual cylinder is screwed 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 become glowing hot and help raise the cylinder temperature. Once the cylinder temperature reaches the desired level, the voltage is limited by the control unit and the glow plug returns to its normal state.
If the PCM detects unexpected resistance with the glow plug for cylinder #1, a P06C5 code will be stored and a Malfunction Indicator Lamp (MIL) may be illuminated.
How Severe Is This DTC?
Any code related to the glow plug will likely be accompanied by driving issues. A stored P06C5 code should be addressed urgently.
What Are Some of the Symptoms of the Code?
Symptoms of a P06C5 trouble code may include:
Excessive black smoke from the exhaust
Engine running issues
Delayed engine starting
Reduced fuel efficiency
Engine misfire codes may be stored
What Are Some of the Common Causes of the Code?
Causes
of this P06C5 fuel injector code may include:
Faulty glow plug(s)
Open or shorted glow plug circuit
Loose or faulty glow plug connector
Faulty glow plug timer
What Are the P06C5 Troubleshooting Steps?
A diagnostic scanner, a reliable vehicle information source, and a digital volt/ohmmeter (DVOM) will be necessary to reach an accurate diagnosis for a P06C5 code. Use the vehicle information source to look up applicable Technical Service Bulletins (TSBs). If you find a TSB that matches the vehicle’s make and model, the symptoms presented, and the stored code, it will help you make a diagnosis.
You may also need to obtain diagnostic flowcharts, wiring diagrams, connector face views, connector pinout diagrams, component locations, and component testing procedures/specifications from the vehicle information source. All of this information will be needed to correctly diagnose the stored P06C5 code.
After performing a careful visual inspection of all glow plug control cables and connectors and the glow plugs themselves, connect the diagnostic scanner to the vehicle’s diagnostic port. Now, retrieve all stored codes and freeze frame data and record them for later (in case you need them). Next, I would test drive the vehicle to see if the P06C5 code resets. Drive until one of two things happens: either the PCM enters readiness mode, or the code resets. If the code resets, proceed with the diagnosis. If not, you are dealing with an intermittent condition that may need to worsen before an accurate diagnosis can be made.
Be careful not to burn yourself or start a fire when performing this test. My usual method for testing glow plugs is to remove them and apply battery voltage. If the glow plug becomes bright red, it is good. If it does not heat up and glow, it is faulty. In the case of the stored P06C5 code, you will want to take the time to test it with your DVOM. If it does not meet the manufacturer’s resistance specifications, consider it faulty.
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 to the glow plug timer or glow plug controller. Test all associated fuses and relays according to the manufacturer’s recommendations. Typically, I have found it preferable to test system fuses and fuse links with the circuit under load. A fuse in an unloaded circuit may appear functional (when it is not) and lead you down the wrong diagnostic path.
If all fuses and relays appear functional, use the DVOM to test the output voltage at the glow plug timer or PCM (wherever they originate from). If voltage is detected at the glow plug timer or PCM, suspect that you have an open or shorted circuit. You can search for the cause of the discrepancy or simply replace the circuit.
Attempting to diagnose the wrong cylinder is more common than you might think. Save yourself a headache and make sure you are addressing the correct cylinder before beginning your diagnosis.