P068E — Cylinder 8 Glow Plug Control Circuit Low #

Note: The code description can vary depending on the vehicle manufacturer.

• P068E: Glow Plug Control Circuit Low – Cylinder 8 (General, SAE)
• P068E: Cylinder 8 Glow Plug Control Circuit Low Voltage (Ford, GM, FCA/Stellantis)
• P068E: Glow Plug #8 Control Circuit – Low (Mercedes-Benz, Sprinter)
• P068E: Glow Plug 8 Low Circuit (Nissan, Renault, Opel/Vauxhall)

Summary of code P068E #

The P068E diagnostic trouble code (DTC) indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an abnormally low voltage or current condition within the glow plug control circuit for cylinder 8. Glow plugs are heating devices used in diesel engines to preheat the combustion chambers and ensure easier starting, especially in cold conditions. This code is most often found in V8 diesel engines where each cylinder has a dedicated glow plug and control circuit. When the ECM/PCM detects a problem with the electrical control or operation of glow plug #8, it stores P068E and may illuminate the check engine light. Addressing this code promptly is crucial for reliable cold starts and to prevent possible cylinder misfires or emissions issues.

Common symptoms for code P068E #

A vehicle with a stored P068E code may show signs that are sometimes subtle, especially in mild weather, but can be quite pronounced in cold climates. The most typical symptoms include:

• Hard starting or extended cranking, especially when cold
• Rough idle immediately after startup
• Visible white or gray exhaust smoke on cold start
• Check Engine Light illuminated
• Engine misfire shortly after ignition
• Reduced engine performance in cold conditions

Probable causes for code P068E (in order of likelihood) #

Several issues can trigger the P068E code, ranging from electrical faults to failed components. The most prevalent causes are:

1. Faulty glow plug in cylinder 8: The heating element may have burned out or failed internally.
2. Open or shorted wiring in the glow plug circuit: Damaged, corroded, or disconnected wires/connectors between the ECM/PCM and glow plug #8.
3. Defective glow plug control module/relay: The module or relay responsible for energizing the glow plugs may be malfunctioning.
4. Poor electrical connections: Loose or corroded terminals at the glow plug, relay, or ECM/PCM.
5. ECM/PCM software or internal fault: Rare, but possible if all else checks out.

Step-by-step diagnostic for code P068E #

Diagnosing P068E involves a logical, methodical approach to ensure the true cause is addressed. Here is a technician-approved workflow:

• 1. Confirm the code: Use a scan tool to verify P068E is active and check for related codes, like other glow plug circuit errors.
• 2. Inspect the glow plug: Test the resistance of glow plug #8 with a digital multimeter (should match the OEM specified range, usually 0.5–2.0 ohms). Replace if open or out of spec.
• 3. Check the wiring and connectors: Visually inspect harnesses and terminals for signs of corrosion, burning, or physical damage. Wiggle-test connectors while monitoring live data for changes.
• 4. Test the glow plug control module/relay: Check for proper output voltage to glow plug #8 during pre-glow phase. Compare to other cylinders if possible.
• 5. Verify ECM/PCM signals: If all external hardware is healthy, use wiring diagrams to check for control signals and continuity between the ECM/PCM and glow plug circuit.
• 6. Clear codes and retest: After repairs, reset the codes and monitor operation during a cold start to ensure the repair was successful.

Possible repairs for code P068E #

Once the root cause is found, the repair should directly address the specific fault. Common fixes include:

• Replace the faulty glow plug in cylinder 8 if it tests open or outside OEM resistance specs.
• Repair or replace damaged wiring or connectors in the glow plug #8 circuit.
• Replace the glow plug control module or relay if it fails output or continuity testing.
• Clean and secure all electrical connections related to the glow plug system.
• Update or reprogram the ECM/PCM if a technical service bulletin (TSB) applies or if a rare internal fault is confirmed.

Can you drive with code P068E? #

Yes, but with limitations. While P068E will not usually cause immediate engine damage, driving with this code can lead to difficult cold starts, increased exhaust emissions, and rough running after startup, especially in colder climates. If multiple glow plugs are affected, or if you regularly operate in low temperatures, you risk battery drain, repeated misfire, or increased wear. It’s best to address the fault soon for reliable operation and to minimize potential long-term damage.

Vehicles most commonly affected by code P068E #

P068E is primarily found in modern diesel engines with individual glow plug monitoring, especially those equipped with V8 configurations. The following vehicles are most frequently reported with this code:

• Ford Super Duty (F-250, F-350, 6.7L Power Stroke V8 Diesel)
• Chevrolet Silverado/GMC Sierra (2500HD/3500HD, 6.6L Duramax Diesel V8)
• RAM 2500/3500 (6.7L Cummins Diesel V8)
• Mercedes-Benz Sprinter (V8 diesel variants)
• Nissan Titan XD (5.0L Cummins V8 Diesel)
• Opel/Vauxhall Movano, Renault Master (V8 diesel variants)

Common mistakes & best practices for code P068E #

Misdiagnosis often leads to unnecessary parts replacement or overlooked wiring issues. To avoid wasted time and money, keep these in mind:

• Don’t replace the glow plug without testing it first. A wiring or control module fault can trigger the same code.
• Always inspect wiring and connectors for damage or corrosion before replacing expensive modules.
• Use the correct OEM glow plug for your engine. Aftermarket plugs may not match resistance specs or durability.
• Never ignore related codes. Multiple glow plug codes often indicate a shared module or relay issue.
• Clear all codes and verify repair by performing a true cold start test.

Quick FAQ for code P068E #

Q: Is it safe to ignore a P068E code if the engine still starts?
A: While you may be able to start and drive, repeated cold starts with an inoperative glow plug can increase engine wear, emissions, and battery strain. It’s best to have it fixed for long-term reliability.

Q: Can I replace just one glow plug or should I do all at once?
A: Only the faulty glow plug (in this case, cylinder 8) requires replacement. However, if your engine has high mileage and other plugs are original, preventive replacement of the full set may save future labor and downtime.