Glow plug failures are one of the most common issues affecting Sprinter diesel engines, particularly in colder climates. Whether you’re dealing with a no-start condition in winter or mysterious fault codes on your dashboard, understanding glow plug symptoms and how to diagnose and fix them can save you hundreds of dollars and keep you on the road.

This guide covers everything Sprinter owners need to know about glow plug failures: how they work, what symptoms to watch for, the fault codes that trigger your check engine light, DIY replacement procedures, and preventative maintenance strategies.

How Sprinter Glow Plugs Work

Diesel engines rely on glow plugs to pre-heat the combustion chamber during cold starts. Unlike gasoline engines that use spark plugs, diesel engines ignite fuel through compression heat alone. When outside temperatures drop, the air inside the engine chamber becomes too cold to ignite fuel efficiently, so glow plugs electrically heat the combustion chamber to aid the ignition process.

Sprinter glow plug count varies by generation:

  • NCV3 (2007–2018) with OM642 V6: 6 glow plugs (one per cylinder)
  • VS30 (2019+) with OM654 I4: 4 glow plugs (one per cylinder)

The glow plug control module monitors engine temperature and activates glow plugs for 1–5 seconds after key-on (depending on ambient temperature) to prepare the engine for starting. Once the engine fires and reaches operating temperature, the glow plugs deactivate automatically.

Symptoms of Glow Plug Failure

A single failed glow plug often doesn’t prevent starting, but multiple failures or a complete control module fault will. Watch for these warning signs:

  • Hard starting in cold weather — engine takes longer to turn over; may require multiple key cycles to ignite
  • No start or won’t start below 40°F — vehicle cranks but doesn’t fire
  • Check engine light (MIL) on dashboard — with glow plug–specific fault codes
  • Rough idle after cold start — misfiring or uneven combustion in one or more cylinders
  • White or black smoke on cold start — unburned or over-rich fuel due to poor ignition
  • Limp mode activation — if glow plug fault code triggers emissions thresholds
  • Clicking sound on key-on — glow plug relay attempting to energize a dead circuit

Glow Plug Fault Codes

When the glow plug system detects a problem, the engine control module stores a diagnostic trouble code (DTC) and illuminates the check engine light. Here are the most common codes on Sprinters:

P0380 – Glow Plug System Malfunction

This is a generic code that signals a fault anywhere in the glow plug circuit. It typically means:

  • One or more glow plugs have failed and are not drawing current
  • The glow plug relay is faulty and not supplying voltage
  • The glow plug control module is defective
  • Wiring harness damage between the module and glow plugs
  • Low battery voltage preventing proper glow plug energization

P0380 is the most common glow plug code you’ll see. It requires further diagnosis to pinpoint which component has failed.

P0381 – Glow Plug System Low Voltage

The glow plug circuit is not receiving sufficient voltage (typically below 10V) to heat the plugs. Causes include:

  • Weak or failing battery (test voltage at least 12.5V at rest)
  • Corroded battery terminals or loose ground cables
  • Blown or intermittent glow plug fuse
  • Faulty glow plug relay
  • High resistance in the glow plug harness due to corrosion or damage

First step: Check your battery and charge to full capacity. Clean and tighten all battery cable connections before replacing glow plugs.

P0670 – Glow Plug Control Module Fault

The engine control module detects a problem with the glow plug control module itself. This code indicates:

  • Internal glow plug control module failure
  • Communication error between the main ECM and glow plug module
  • Power supply to the glow plug module is interrupted

If this code appears along with other glow plug codes (P0671–P0676), the control module is likely the culprit. Replacement is usually necessary.

P0671–P0676 – Individual Glow Plug Circuit Faults

These codes pin down which specific glow plug has failed:

  • P0671: Glow Plug 1 (Cylinder 1)
  • P0672: Glow Plug 2 (Cylinder 2)
  • P0673: Glow Plug 3 (Cylinder 3)
  • P0674: Glow Plug 4 (Cylinder 4) — common on VS30 I4 engines
  • P0675: Glow Plug 5 (Cylinder 5) — NCV3 V6 only
  • P0676: Glow Plug 6 (Cylinder 6) — NCV3 V6 only

A single P067x code means that one glow plug is open (not conducting) or the heater element inside has burned out. Multiple P067x codes indicate several failed plugs or a wiring harness problem affecting multiple cylinders.

Diagnosing Glow Plug Failure

Visual Inspection

  • Remove the glow plug cover from the top of the engine
  • Inspect the copper connector on each glow plug terminal for corrosion, white/green oxidation, or cracks
  • Check the glow plug harness for visible cracks, melted insulation, or loose connectors
  • Look for oil leakage from glow plug wells (a sign of a leaking glow plug or o-ring failure)

Electrical Testing

Multimeter resistance test (key off):

  • Disconnect the glow plug harness from the top of the engine
  • Set a multimeter to ohms (resistance) mode
  • Probe between the glow plug terminal (with connector still attached) and a ground point (engine block or battery negative)
  • Good glow plug: typically 0.5–2 ohms resistance
  • Failed glow plug: open circuit or infinite resistance (∞)
  • Test each plug individually; if any reads ∞, that plug is dead and must be replaced

Voltage test (key on, glow position):

  • With the key in the on position (before cranking), measure voltage at each glow plug terminal
  • Expect 10–14V for 1–5 seconds, then drops to 0V once the timer expires
  • If voltage doesn’t appear on any plugs, check the relay and control module
  • If voltage is low (below 9V), trace back to the battery, fuses, and harness connectors

Glow Plug Control Module Diagnosis

The glow plug control module is a relay box mounted on or near the engine that distributes power to the glow plugs. If you see P0670 or multiple P067x codes:

  • Visual check: Look for burnt terminals, melted connectors, or water intrusion inside the module
  • Relay test: If accessible, listen for a clicking sound when the key is turned on—this indicates the relay is firing. No click = relay failure
  • Voltage at relay input: With key on, test voltage at the power input terminal of the relay. Should read 12+V. If low, the problem is upstream (battery, fuse, harness)
  • Voltage at relay output: Test the output terminals going to the glow plugs. Should read 10–14V when the relay is energized. If 0V, the relay contacts are stuck open

DIY Glow Plug Replacement

Tools and Parts You’ll Need

Tools:

  • Glow plug socket (typically 8mm or 10mm, depending on your engine—many come with a thin-wall design to fit the deep well)
  • Ratchet wrench and extension (6–10 inch)
  • Wire cutters or pliers to disconnect the glow plug harness
  • Small brush or compressed air to remove carbon and debris from the glow plug well
  • Torque wrench (if replacing plugs; torque spec is typically 15–22 Nm for Sprinter glow plugs)
  • Penetrating oil (PB Blaster, WD-40) for stuck plugs

Parts (for NCV3 or VS30):

  • OEM Bosch glow plugs (recommended) or equivalent aftermarket plugs—part numbers vary by engine year and generation
  • Replacement o-rings or seals (if the wells are leaking)
  • New glow plug harness (only if the existing one is damaged)

Step-by-Step Replacement Procedure

  • 1. Disconnect the battery negative terminal to prevent accidental arcing or short circuits while working near electrical components
  • 2. Remove the glow plug cover — unscrew or unclip the plastic cover on top of the engine to access the glow plugs
  • 3. Disconnect the glow plug harness — carefully pull the connector block (which has individual terminals for each glow plug) straight up and out of the way
  • 4. Clean the glow plug well — use a brush or compressed air to blow out any carbon, dirt, or debris that may have accumulated in the well. This prevents contamination from entering the engine
  • 5. Unscrew and remove the failed glow plug — fit your glow plug socket onto the plug, attach the ratchet and extension, and turn counterclockwise. Some plugs may be seized if the engine has not been started in cold climates for extended periods—apply penetrating oil and let it soak for 15–30 minutes before attempting removal
  • 6. Install the new glow plug — thread the new glow plug by hand first to avoid cross-threading, then tighten with the socket and ratchet to the manufacturer’s torque specification (typically 15–22 Nm). Do not overtighten, as this can crack the ceramic element inside the plug
  • 7. Reconnect the harness — carefully push the connector block back onto the glow plug terminals, ensuring a firm seat. You should hear or feel a click when it snaps into place
  • 8. Reinstall the glow plug cover — screw or clip the cover back in place
  • 9. Reconnect the battery negative terminal and close the engine compartment
  • 10. Start the engine and clear fault codes — turn the key on to allow the glow plug timer to run (you may hear the relay click briefly), then start the engine. Once running, use a diagnostic scanner or visit a repair shop to clear the P0671–P0676 codes from memory

Stuck Glow Plug Extraction

If a glow plug is seized in the cylinder head and won’t budge, here’s a safe extraction method:

  • Apply penetrating oil: Spray PB Blaster or a similar penetrating fluid around the base of the plug where it threads into the head. Let it soak for 30 minutes to several hours (overnight is ideal for very stuck plugs)
  • Gently rock the socket: Attach the ratchet and socket, then gently rock the ratchet back and forth (turning slightly counterclockwise, then back to the starting point) without fully unscrewing. This helps break the corrosion seal without stripping the threads
  • Apply heat (if safe): For severely stuck plugs, a heat gun directed at the cylinder head around the plug for a few minutes can help expand the metal and break the corrosion bond. Do not overheat—aim for 200–250°F maximum, not red-hot
  • Avoid impact tools: Do not use an impact wrench or hammer, as these can crack the ceramic element or snap the glow plug wire inside the hole, making extraction even harder
  • If still stuck: Stop and take the vehicle to a diesel specialist shop. Attempting to force a seized plug can damage the threads in the cylinder head, which is an expensive repair

Glow Plug Control Module Replacement

If your diagnosis points to a failed glow plug control module (P0670 code, or voltage tests show the module isn’t supplying power to the glow plugs), you’ll need to replace the module itself.

Location varies by year and generation:

  • NCV3 (2007–2018): typically mounted on the engine block near the intake manifold or on the inner fender wall
  • VS30 (2019+): usually located on the passenger side near the air intake or inside the engine bay closet

Replacement steps:

  • Disconnect the battery negative terminal
  • Unplug the connector from the glow plug module
  • Disconnect the power and ground wires (note their positions for reinstallation)
  • Unscrew the mounting bolts and remove the old module
  • Install the new module, reattach all connectors and wires, and reconnect the battery
  • Start the engine and scan for codes to confirm the module is now functioning

Cost: A replacement glow plug control module ranges from $150–$400 depending on the source (OEM vs. aftermarket). Labor at a shop typically runs $150–$300.

Cost Breakdown

  • Single glow plug (OEM Bosch): $25–$50 per plug
  • Complete set of plugs (NCV3 6-pack or VS30 4-pack): $120–$250
  • Glow plug control module (OEM): $200–$400
  • Glow plug relay (if separate): $50–$150
  • Labor at a shop (per hour): $100–$150
  • Complete shop replacement (all plugs + module): $600–$1,200

DIY replacement of a single or a few glow plugs can save $300–$500 in labor. If you’re comfortable with basic socket wrench work, it’s one of the most accessible diesel engine repairs.

Preventative Maintenance and Cold-Start Tips

To extend the life of your glow plugs and minimize cold-start issues:

  • Block heater in winter: Plug in your Sprinter overnight during cold weather (below 0°F) to pre-warm the engine coolant. This reduces glow plug stress and improves starting reliability
  • Battery health: Keep your battery charged to full capacity and replace it every 5–7 years. A weak battery forces glow plugs to work harder and shortens their lifespan
  • Fuel quality: Use premium diesel with high cetane rating (45+) to improve ignition characteristics and reduce starting difficulty
  • Idle at startup: Allow 10–30 seconds of idle after a cold start before driving. This lets the glow plugs fully disengage and the engine oil warm up
  • Avoid extended idle in extreme cold: If stranded in below-zero weather, don’t idle for hours—this wastes fuel and stresses the glow plug system. Use a block heater or seek shelter instead
  • Listen for the glow-relay click: When you turn the key on, you should hear a faint clicking sound from the relay area (or feel it vibrate if you’re close). If this sound ever goes away, have the glow plug system diagnosed immediately—it’s a sign the relay or module is failing
  • Inspection interval: Every 60,000 miles (or annually), visually inspect the glow plug connectors for corrosion. Clean with a wire brush if oxidation is visible

When to Seek Professional Help

DIY glow plug replacement is straightforward for most owners, but know when to defer to a professional:

  • Stuck or seized glow plugs: If a plug won’t unscrew after soaking with penetrating oil and gentle rocking, stop and contact a diesel specialist. Forcing it can damage the cylinder head threads
  • Multiple fault codes or module failure: If you see P0670 or many P067x codes together, the issue is likely the control module or wiring harness, not individual plugs. A professional can test these components accurately
  • Limp mode or drivability issues: If your Sprinter is in limp mode or has other symptoms beyond hard starting, there may be additional issues (emissions sensor, turbo boost, EGR) that need diagnosis
  • No improvement after plug replacement: If you replace the glow plugs and the fault codes return, the problem is the module, relay, or harness. Return to the shop for further diagnostics
  • Engine block damage suspected: If you suspect the glow plug hole is cracked or the threads are stripped, this requires professional machine shop repair

Next Steps

If your Sprinter is showing glow plug fault codes or hard-start symptoms:

  • Use the SprinterRVDesk diagnostic tool to confirm your vehicle details and get brand-specific guidance
  • Start with a visual inspection of the glow plug connectors and harness for obvious damage
  • Run a multimeter resistance test on each glow plug to identify which ones have failed
  • Check your battery voltage and terminals before replacing plugs
  • Order OEM Bosch glow plugs specific to your engine (OM642 for NCV3, OM654 for VS30)
  • Allow 1–2 hours for a complete DIY replacement if you’re replacing all plugs in your vehicle
  • Clear fault codes after replacement using a diagnostic scanner
  • Monitor your cold-start performance over the next few weeks to ensure the repair is stable

For detailed guidance on your specific model and fault code, visit the SprinterRVDesk blog or contact us via the contact page.

Last updated: April 2026