P067B — Cylinder 4 Glow Plug Control Circuit High #

Note: The definition and description of code P067B may vary depending on the vehicle manufacturer (OEM).

• P067B — Cylinder 4 Glow Plug Control Circuit High (General, most OEMs)
• P067B — Glow Plug Control Module to Cylinder 4 — Circuit High (Ford)
• P067B — Heater Plug Cylinder 4 Circuit High (Mercedes-Benz)
• P067B — Cylinder 4 Glow Plug Circuit Voltage High (GM/Chevrolet)

Summary of code P067B #

P067B is a diagnostic trouble code (DTC) that indicates the engine control module (ECM)—the computer responsible for managing engine functions—has detected an unusually high voltage in the control circuit for the glow plug in cylinder 4. Glow plugs are electrical heating elements fitted in diesel engine cylinders to assist with cold starting. This code points specifically to an electrical fault, rather than a failed plug itself. The “high” designation suggests the circuit is seeing higher than expected voltage, often due to wiring or control issues. Addressing this issue promptly is crucial for maintaining optimal cold-start performance and preventing further electrical damage.

Common symptoms for code P067B #

When P067B is present, your diesel vehicle may exhibit a range of symptoms—some subtle, others more obvious. The most common is difficulty starting the engine in cold weather, as the glow plug system is essential for igniting the diesel-air mixture. You may also notice warning lights on the dashboard, such as the “Check Engine” or the glow plug indicator. In some cases, you might experience rough idle or increased smoke during startup, but not always.

• Hard starting, especially in low temperatures
• Extended cranking time before engine fires
• “Check Engine” or glow plug warning light illuminated
• Rough idle after cold start
• Excessive white or gray smoke from exhaust during startup
• No noticeable symptoms in mild climates or warm starts

Most likely causes for code P067B #

The root causes of P067B are primarily electrical in nature. High circuit voltage is generally the result of an open circuit, poor ground, or a wiring harness issue. Component failure, such as a faulty glow plug relay or control module, is less common but possible. The following list ranks causes from most to least frequent based on typical field diagnostics:

1. Open circuit or high resistance in the glow plug wiring to cylinder 4
2. Poor or corroded ground connection in the glow plug circuit
3. Faulty glow plug relay or glow plug control module
4. Damaged or unplugged glow plug for cylinder 4
5. Corroded or loose electrical connectors at the glow plug or control module
6. Short to voltage in the harness (less common)
7. ECM (Engine Control Module) internal fault (rare)

Step-by-step diagnostic for code P067B #

A methodical diagnostic approach is essential to pinpoint the exact cause of P067B. Skipping steps may lead to unnecessary parts replacement or unresolved issues. Here’s a proven workflow for technicians:

• 1. Scan for additional codes: Check for related DTCs, especially other glow plug or control module codes.
• 2. Visual inspection: Examine cylinder 4 glow plug and its wiring for signs of damage, corrosion, or loose connections.
• 3. Check electrical connectors: Unplug and inspect the glow plug connector and the connections at the control module for corrosion, bent pins, or moisture.
• 4. Test glow plug resistance: Using a digital multimeter, measure the resistance of cylinder 4’s glow plug. Compare to OEM specifications (typically 0.6–2 ohms for most vehicles).
• 5. Verify circuit continuity: Check for continuity (no open circuit) between the control module and the glow plug pin for cylinder 4.
• 6. Inspect ground circuit: Ensure the ground path for the glow plug is clean, tight, and free of corrosion.
• 7. Check for short to voltage: With ignition off, check if there’s unexpected voltage present at the glow plug circuit—this could indicate a harness issue.
• 8. Test the glow plug relay/module: If all wiring and the glow plug check out, test or substitute the relay/control module as per OEM procedures.
• 9. Clear codes and retest: After any repair, clear all codes and verify if P067B returns during a cold start cycle.

Possible repairs for code P067B #

The right repair action depends on which fault your diagnosis uncovers. Here are targeted solutions for each major cause of P067B:

• Repair or replace damaged wiring between the glow plug control module and cylinder 4 glow plug
• Clean and secure all ground connections related to the glow plug circuit
• Replace corroded, loose, or damaged connectors at the glow plug or module
• Replace the cylinder 4 glow plug if resistance is out of spec or the plug is open
• Replace a faulty glow plug relay or glow plug control module as diagnosed
• Repair any short-to-voltage in the wiring harness if found
• In very rare cases, repair or replace the ECM (only after all other avenues are exhausted)

Is it safe to drive with code P067B? #

Limited. While code P067B will not usually cause immediate engine damage, driving with a faulty glow plug circuit can make cold starts difficult or even impossible in low temperatures. This can leave you stranded or contribute to incomplete combustion, leading to increased exhaust smoke and potential long-term engine wear. If you live in a cold climate or rely on reliable cold starts, address this code as soon as possible. In warmer climates, short-term driving may be possible, but don’t ignore the issue.

Vehicles most commonly affected by code P067B #

While P067B can appear on any modern diesel vehicle using individual cylinder glow plug monitoring, it is most frequently reported on certain makes and models, especially those with advanced glow plug control modules. If you drive one of the following vehicles, this code may be more familiar:

• Ford Super Duty (F-250, F-350, 6.7L Power Stroke)
• Chevrolet Silverado and GMC Sierra (Duramax 6.6L)
• Ram 2500/3500 (Cummins 6.7L)
• Mercedes-Benz Sprinter (OM642, OM651 engines)
• Volkswagen/Audi TDI models
• BMW diesel models (X5, 3 Series diesel)

Common mistakes & best practices for code P067B #

Misdiagnosis of P067B is often due to skipping basic inspection steps or replacing parts without testing. Here are classic pitfalls and how to avoid them:

• Assuming the glow plug itself is always the cause—test resistance before replacing
• Overlooking corroded or loose connectors—always inspect and clean before condemning components
• Neglecting the ground circuit—poor ground can trigger high circuit voltage
• Replacing the glow plug control module prematurely—verify wiring and plug before module replacement
• Not clearing codes after repairs—always clear and recheck to confirm fix

Quick FAQ — P067B #

Q: Will my diesel still start with P067B present?
A: It may, especially in warm weather. However, you could experience hard starting or rough idle in cold conditions, and eventually, the engine may fail to start if more glow plugs or circuits fail.

Q: Can a failing battery cause P067B?
A: Not directly. A weak battery may cause slow cranking or other glow plug codes, but P067B specifically indicates high voltage in the circuit—usually a wiring, connector, or control fault, not battery-related.