P1401 — Glow Plug Monitor Fault (Bank #2)

What does OBD2 code P1401 mean?

Glow Plug Monitor Fault (Bank #2) (P1401): a powertrain (engine/transmission) fault affecting the diesel glow plug system. The car is usually drivable while you plan the repair. Most often caused by burned-out glow plug, corroded glow plug connectors, damaged glow plug wiring or connector.

Is it safe to drive with P1401?

Safe to drive once the engine is started and warmed up. The main risk is cold-weather starting: with several dead plugs the engine may not start on a cold morning. Fix before winter.

How much does it cost to fix P1401?

Replace a full set of glow plugs — $250–$600; Replace the glow plug relay/module — $150–$450; Replace one glow plug — $80–$200. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

What are the symptoms of P1401?

Drivers most often notice: glow plug warning light staying on, Check Engine Light on, rough idle until warmed up, white smoke after a cold start.

Will P1401 clear itself?

Sometimes P1401 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

When temperatures drop, diesel engines face a unique challenge: the combustion process that powers them depends heavily on heat, and cold cylinders struggle to ignite fuel efficiently. Diesel glow plugs solve this by creating localized heat in each cylinder's combustion chamber, essentially giving the fuel a hot surface to ignite against during startup. On V-style diesel engines, cylinders are organized into two banks—bank 1 and bank 2—and P1401 targets the second bank specifically. The engine control module doesn't just fire these plugs blindly; it monitors their performance through a feedback circuit, watching for proper resistance and current flow. When that monitor circuit detects something wrong with bank 2's glow plug system, P1401 gets stored.

The key thing to understand about P1401 is that it represents a verified fault, not a momentary glitch. The ECU runs multiple checks under specific operating conditions before activating the malfunction indicator lamp. Each time the module confirms the abnormal reading, it logs the event—and the freeze frame data captures engine load, RPM, coolant temperature, and vehicle speed at that exact moment. This snapshot is your best starting point for diagnosis because it tells you precisely what conditions triggered the code. Before you clear P1401 and hit the road, save that freeze frame; you'll need those numbers to reproduce the fault during testing.

Common Symptoms

P1401 doesn't hide its presence for long. You'll likely see the glow plug warning lamp illuminated on the dashboard, sometimes staying on well after the engine reaches operating temperature. The Check Engine light may accompany it or appear on its own, depending on your vehicle's programming. As the affected cylinders struggle to combust properly, the engine typically runs rough during warm-up, producing noticeable vibration and irregular RPM until things heat up. That incomplete combustion shows up visually too—expect billowing white smoke from the exhaust pipe after a cold start. Perhaps most frustratingly, hard starting becomes the norm in cold weather, with the engine cranking longer than it should or refusing to start entirely until temperatures rise.

Typical Causes

The most frequent culprit behind P1401 is corrosion at the glow plug electrical connectors. Moisture, road salt, and thermal cycling work together to degrade the connection points, increasing resistance until the monitor circuit detects the anomaly. A faulty glow plug relay or control module ranks second—these components handle the high current needed to heat the plugs, and they can fail internally or overheat. Damaged wiring in the glow plug harness, whether from chafing against engine components, heat damage, or accidental pinches during repairs, creates open or high-resistance circuits. A blown fuse in the glow plug power circuit will obviously prevent operation, and while less common, a burned-out glow plug itself will trigger the monitor fault when it fails to draw expected current.

How to Diagnose

Start by connecting an OBD2 scanner and retrieving all stored codes—save the freeze frame data before you do anything else, as this recording shows exactly what was happening when P1401 appeared. After noting any additional trouble codes, check manufacturer technical service bulletins for your specific make and model; some vehicles have known issues with the glow plug system that have published fixes or software updates. Next, perform a thorough visual inspection of the bank 2 glow plug wiring harness and connectors, looking for damaged insulation, corrosion buildup, loose terminals, or evidence of heat damage. Measure the resistance of each glow plug in bank 2 with a multimeter—an open circuit or infinite reading indicates a failed plug, while healthy plugs typically show 0.5 to 2 ohms depending on the design. Verify proper voltage delivery by checking the glow plug rail during the pre-glow cycle with a test light or multimeter. Finally, clear the codes, complete a full drive cycle including the conditions from the freeze frame data, and reconnect your scanner to confirm P1401 does not return.

Repair Options and Costs

When addressing P1401, tackle the inexpensive possibilities before considering major component replacement. Corroded connectors often need nothing more than cleaning with electrical contact cleaner and dielectric grease—a minimal expense if you do it yourself. A single failed glow plug runs $80 to $200 for parts, or $150 to $300 with professional labor. The glow plug relay or control module, if faulty, requires replacement at $150 to $450 for parts and installation. Replacing a full set of glow plugs in bank 2 costs between $250 and $600 depending on vehicle and labor rates.

Total Repair Cost

Most P1401 repairs fall somewhere between $80 and $600 total. The wide range reflects how many cylinders need attention and whether you handle labor yourself. An accurate diagnosis before purchasing parts is the single best way to control costs—the most expensive scenario is rarely where you should start.

Can You Drive with P1401?

Once the engine reaches normal operating temperature, the vehicle drives normally and poses no safety hazard. The practical risk appears during cold starts: with multiple weak or failed plugs, the engine may not start at all on a frigid morning, leaving you stranded. If winter approaches or you live in a cold climate, address this code before temperatures drop.

Related OBD2 Codes

• P1400: Glow Plug Monitor Fault (Bank #1)
• P1402: System Voltage Out Of Self Test Range
• P1403: VVT Solenoid B Circuit High Input
• P1404: Glow Plug Circuit High Side
• P1405: DPFE Circuit Low Input
• P1406: DPFE Circuit High Input