P068F — Cylinder 8 Glow Plug Control Circuit High #

Note: The code description for P068F may vary depending on the vehicle manufacturer.

• P068F: Cylinder 8 Glow Plug Control Circuit High (General)
• P068F: Cylinder 8 Glow Plug Circuit High (Ford, GM, Chrysler)
• P068F: Glow Plug Control Module Circuit High – Cylinder 8 (Mercedes-Benz)
• P068F: Glow Plug Output High – Cylinder #8 (RAM)

Summary of code P068F #

The P068F diagnostic trouble code indicates that the engine control module (ECM) or powertrain control module (PCM) has detected an abnormally high voltage or current level in the glow plug control circuit for cylinder 8. The glow plug is a crucial component in diesel engines, responsible for pre-heating the combustion chamber to ensure smooth cold starts. When the control circuit voltage is too high, it often points to an electrical problem such as an open circuit, damaged wiring, or an issue with the glow plug relay or controller. This code usually triggers the check engine light and may affect engine performance, especially in cold conditions. Depending on the OEM (Original Equipment Manufacturer) and vehicle model, the detection criteria and system response may differ, but the underlying concern remains related to electrical irregularities within the cylinder 8 glow plug circuit.

Frequent symptoms for code P068F #

A diesel engine with the P068F code often exhibits symptoms related to starting and combustion efficiency, particularly in cold weather. The presence and severity of symptoms may vary depending on whether the issue is intermittent or persistent.

• Extended engine cranking or hard starting, especially in cold temperatures
• Rough idle after startup
• Engine misfire or hesitation during initial running
• Illuminated check engine light (CEL or MIL)
• Possible increase in white exhaust smoke at start-up
• Reduced engine performance until the engine warms up

Most likely causes for code P068F #

The P068F code is most commonly linked to an electrical fault in the glow plug circuit for cylinder 8. Here are the most frequent causes, listed in order of likelihood:

1. Open circuit or high resistance in the glow plug wiring harness
2. Faulty or disconnected glow plug (cylinder 8)
3. Defective glow plug control module or relay
4. Corroded or loose electrical connectors at the glow plug or module
5. PCM/ECM software or internal failure (rare)

Step-by-step diagnosis for code P068F #

A methodical approach is key to accurately diagnosing the root cause of P068F. Here’s a proven step-by-step process for technicians and experienced DIYers:

• Step 1: Confirm the code and clear any existing codes. Re-scan after a cold start to verify if P068F returns.
• Step 2: Visually inspect the wiring harness and connectors leading to cylinder 8’s glow plug and the glow plug control module for signs of damage, corrosion, or disconnection.
• Step 3: Using a digital multimeter, check for proper voltage supply and ground at the affected glow plug connector with the ignition on.
• Step 4: Measure resistance of the cylinder 8 glow plug (should be within OEM specification, typically less than 1–2 ohms when cold).
• Step 5: Test continuity between the control module and glow plug; look for open circuits or excessive resistance.
• Step 6: Inspect the glow plug control module or relay for operation and output voltage.
• Step 7: If all hardware checks out, consider a software update or further PCM/ECM diagnostic as per OEM procedures.

Possible repairs for code P068F #

Once you have identified the cause of the P068F code, targeted repairs can restore proper glow plug function. Typical solutions include:

• Repairing or replacing damaged, corroded, or loose wiring/connectors in the cylinder 8 glow plug circuit
• Replacing the faulty cylinder 8 glow plug with an OEM-approved unit
• Replacing the glow plug control module or relay if it fails output or control tests
• Cleaning and securing all related electrical connections
• Reprogramming or replacing the PCM/ECM if diagnosed as faulty (rare and last resort)

Is it safe to drive with code P068F? #

Driving with code P068F is generally possible, but only for a limited time and with caution. The main risk is difficulty starting the engine and increased emissions, especially in cold weather. Ignoring this code may lead to persistent cold-start problems, rough running, and potential long-term damage to the diesel particulate filter (DPF) due to incomplete combustion. If frequent hard starts or rough idle are present, repair should be prioritized to avoid further complications.

Vehicles most commonly affected by code P068F #

While P068F is an OBD-II standard code, it is most frequently reported on modern diesel vehicles equipped with individual cylinder glow plug monitoring. The following makes and models are commonly associated:

• Ford Super Duty pickups (F-250, F-350) with Power Stroke diesel engines
• Chevrolet Silverado/GMC Sierra HD with Duramax diesel
• RAM 2500/3500 with Cummins diesel
• Mercedes-Benz Sprinter vans (various diesel engines)
• Some recent Volkswagen/Audi TDI models

Common mistakes and best practices for code P068F #

Misdiagnosis can lead to unnecessary parts replacement and recurring issues. To avoid these pitfalls and ensure a lasting repair:

• Do not replace all glow plugs without confirming which cylinder is faulty
• Avoid ignoring the code if symptoms are mild—early repair prevents further damage
• Always test the wiring and control module before replacing glow plugs
• Double-check for TSBs (Technical Service Bulletins) or recalls related to glow plug system issues for your vehicle
• Use only OEM or OEM-equivalent replacement parts for best reliability

Quick FAQ for code P068F #

Still have questions? Here are concise answers to common queries:

• Q: Can a single glow plug cause starting problems?
  A: Yes, especially in cold weather, a failed glow plug in one cylinder (like cylinder 8) can make starts rough and prolong cranking, even if the other plugs work.
• Q: Will clearing the code fix the problem?
  A: Clearing the code will turn off the warning light temporarily, but unless the underlying cause is repaired, the P068F code will likely return upon the next cold start.