P067C — Cylinder 5 Glow Plug Control Circuit Low #

The code description may vary depending on the vehicle manufacturer. Always consult your OEM documentation for the exact wording used on your vehicle.

Known description variations for P067C:

• Cylinder 5 Glow Plug Control Circuit Low (Generic/OEMs)
• Cylinder 5 Glow Plug Circuit Low Voltage (Ford)
• Glow Plug/Heater Circuit Low – Cylinder 5 (GM/Chevrolet)
• Cylinder 5 Glow Plug Low Voltage Detected (Mercedes-Benz)

Summary of code P067C #

P067C is a diagnostic trouble code (DTC) that points to a problem within the glow plug control circuit for cylinder 5. Glow plugs are electrical heating elements used in diesel engines to assist with cold starting by warming the combustion chamber. This code indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected lower-than-expected voltage when controlling the glow plug in cylinder number 5. This can lead to starting difficulties, increased emissions, or even potential engine misfires, especially in cold weather. Prompt diagnosis and repair are essential to avoid further complications and to ensure reliable engine operation.

Frequent symptoms for code P067C #

When P067C is present, symptoms can be subtle or quite noticeable, depending on the severity and ambient temperature. Drivers may find their vehicle harder to start, especially on cold mornings, or notice rough idling after startup. In most cases, the Check Engine Light (CEL) will illuminate. Sometimes, performance issues are limited to initial startup, while other times, drivability can be noticeably affected.

Common symptoms include:

• Illuminated Check Engine Light (CEL)
• Hard starting, especially in cold weather
• Rough idle after cold start
• Increased white smoke from exhaust on startup
• Possible engine misfire (especially after cold soak)
• Reduced engine performance right after startup

Probable causes for code P067C #

The most frequent root causes of P067C typically relate to the glow plug itself, the wiring, or the control module. Since glow plug circuits operate in harsh environments (heat, vibration, moisture), components are prone to wear and corrosion over time. Below is a list of probable causes, ranked from most to least likely based on common field experience:

1. Faulty glow plug in cylinder 5 (open or shorted internally)
2. Damaged or corroded wiring/connectors in the cylinder 5 glow plug circuit
3. Faulty glow plug control module/relay (unable to supply correct voltage)
4. Blown fuse affecting the glow plug circuit
5. ECM/PCM failure (rare, but possible if all else checks out)

Step-by-step diagnosis for P067C #

Diagnosing P067C involves systematically narrowing down the source of low voltage detected by the ECM/PCM. Always begin with a visual inspection and basic electrical tests before considering component replacement. Proper diagnostic tools, like a digital multimeter and scan tool with live data capability, are recommended.

Step-by-step diagnostic process:

1. Read all stored codes and freeze-frame data to capture the conditions when the code set.
2. Visually inspect the glow plug harness and connectors at cylinder 5 for damage, corrosion, or loose connections.
3. Check voltage at cylinder 5 glow plug using a multimeter during cold start cycle (should match OEM specs).
4. Test glow plug resistance (with engine off and plug disconnected). Compare to manufacturer specification; out-of-spec readings indicate a faulty plug.
5. Inspect related fuses and relays for continuity and correct operation.
6. Test wiring continuity from the glow plug to the control module or relay; look for breaks or excessive resistance.
7. Check the glow plug control module output with an oscilloscope or multimeter. Ensure it supplies correct voltage/current.
8. If all else is OK, check ECM/PCM outputs, but only after verifying all prior steps.
9. Clear codes and retest after each repair to confirm the issue is resolved.

Possible repairs for P067C #

Once the cause of P067C is identified, repairs should be targeted and thorough. Always use OEM or equivalent quality parts, and double-check all connections after reassembly. Here are the most common repairs, each linked to its underlying cause:

• Replace faulty glow plug in cylinder 5 (if resistance or visual check fails).
• Repair or replace damaged wiring/connectors in the glow plug circuit.
• Replace faulty glow plug control module/relay if it cannot supply correct voltage.
• Replace blown fuse and investigate root cause of overcurrent.
• Replace or reprogram ECM/PCM only if all other components are confirmed good (rare).

Is it safe to drive with code P067C? #

Limited: Proceed with caution. While P067C will not typically cause immediate engine damage, driving with a faulty glow plug circuit can lead to hard starting, excessive white smoke, and rough engine operation—especially in cold climates. Repeated cold starts with inoperative glow plugs can cause increased engine wear, fouled injectors, or even unburned fuel accumulation in the exhaust. For best reliability and to avoid further complications, address this code as soon as possible.

Vehicles most commonly affected by P067C #

P067C is most frequently seen on diesel-powered vehicles equipped with individual cylinder glow plug monitoring. This includes many modern cars, trucks, and vans from both domestic and European OEMs. Some models are particularly prone due to engine layout or known harness wear points.

Commonly affected vehicles:

• Ford Super Duty (F-250, F-350) with Power Stroke diesel
• Chevrolet Silverado/GMC Sierra with Duramax diesel
• Dodge Ram with Cummins diesel
• Mercedes-Benz Sprinter (and related vans)
• Volkswagen/Audi TDI models
• Opel/Vauxhall diesel models

Common mistakes & best practices for P067C #

Proper diagnostic technique is essential to avoid unnecessary parts replacement or recurring issues. Here are the most common pitfalls and professional tips to ensure a successful repair:

• Mistaking a wiring fault for a bad glow plug: Always measure resistance and check wiring continuity before replacing the plug.
• Neglecting to inspect connectors: Corrosion or loose pins at connectors can easily trigger this code.
• Replacing only the failed glow plug: If one plug fails due to age, others may soon follow. Consider replacing all if mileage is high.
• Forgetting to clear codes and confirm repair: Always verify the fix by clearing codes and validating operation with a cold start.
• Using non-OEM glow plugs: Low-quality aftermarket plugs may not meet OEM resistance specs and can cause repeat failures.

Quick FAQ for code P067C #

Below are answers to common questions about this code, straight from the shop floor:

Q: Can a faulty glow plug in cylinder 5 cause other cylinders to set codes?
A: Generally, each cylinder’s glow plug is monitored independently. However, wiring harness issues or a shared control module fault may cause multiple cylinder codes to appear.

Q: Is it necessary to replace the glow plug control module if only one plug or circuit is faulty?
A: Not always. If only one cylinder is affected and the module passes all tests, replacement is not needed. Only replace the module if it fails output or continuity checks, or if multiple unrelated glow plug codes are present.