P1395

What Does Code P1395 Mean?

The OBD-II diagnostic trouble code P1395 signifies a “Glow Plug Monitor Fault” specifically for Engine Bank #1. This code indicates that the Engine Control Module (ECM), also commonly referred to as the Powertrain Control Module (PCM), has detected an inconsistency or malfunction within the glow plug monitoring circuit for the glow plugs located on cylinder bank #1. In diesel engines, glow plugs are critical for initiating combustion, especially during cold starts. They heat the air within the combustion chamber to a temperature sufficient for fuel auto-ignition. The ECM/PCM continuously monitors the operational status of the glow plug system, often through a Glow Plug Control Module (GPCM) or integrated relays.

The monitoring process typically involves the ECM/PCM checking for correct electrical resistance, current draw, or voltage drop across individual glow plugs or the glow plug circuit during and after their activation cycle. When the ECM/PCM detects a reading that falls outside of the manufacturer’s specified parameters for Bank #1 – such as an open circuit (infinite resistance), a short circuit (zero resistance), excessively high or low current draw, or an incorrect voltage signal from the monitoring circuit – it interprets this as a fault in the glow plug system’s ability to operate as commanded or be accurately monitored. Bank #1 refers to the engine bank that contains cylinder number one, which is typically the right bank of a V-configured engine or the only bank on an inline engine. This code points to a problem with the feedback or control integrity rather than merely a glow plug being open, although a faulty glow plug is often the root cause that triggers the monitor fault.

Common Symptoms

• Check Engine Light (CEL) Illumination: The Malfunction Indicator Lamp (MIL) on the dashboard will illuminate.
• Difficulty Starting Engine: Particularly noticeable in cold weather or after long periods of inactivity.
• Rough Idling: The engine may run rough or misfire immediately after a cold start until it reaches operating temperature.
• White Smoke from Exhaust: Unburnt fuel due to insufficient combustion can lead to excessive white smoke, especially during cold starts.
• Reduced Engine Performance: The engine might experience a lack of power or sluggish acceleration until it warms up.
• Increased Emissions: Incomplete combustion contributes to higher levels of pollutants in the exhaust.
• Engine Hesitation: The engine may hesitate or stumble during initial acceleration after a cold start.

What Causes the Code P1395?

• Faulty Glow Plugs: One or more glow plugs on Bank #1 may be open-circuited, short-circuited, or have excessively high internal resistance, leading to improper current draw or complete failure to heat.
• Malfunctioning Glow Plug Control Module (GPCM) or Relay: The GPCM is responsible for supplying power to the glow plugs and often contains the monitoring circuitry. A fault within the module itself, its internal relays, or its monitoring components can trigger this code.
• Damaged Wiring Harness or Connectors: Open circuits, shorts to ground or power, excessive resistance due to corrosion, or loose connections in the wiring between the GPCM and the glow plugs on Bank #1. This includes the main power supply wiring and signal wires.
• Blown Fuse: A fuse protecting the glow plug circuit for Bank #1 may be blown, preventing power delivery to the glow plugs.
• Corroded Terminals: Corrosion on glow plug terminals, GPCM terminals, or harness connectors can impede electrical flow and distort monitoring signals.
• Faulty Engine Control Module (ECM/PCM): Although less common, an internal fault within the ECM/PCM’s glow plug control or monitoring circuit can lead to an erroneous P1395 code.

How to Diagnose and Troubleshoot

Diagnosing P1395 requires a systematic approach, often utilizing an OBD-II scanner and a digital multimeter (DMM).

1. Retrieve and Analyze Codes: Connect an OBD-II scanner to the vehicle’s DLC. Confirm P1395 is present. Check for any other related codes that might provide additional context (e.g., specific glow plug circuit low/high codes). Review freeze frame data to understand the engine’s operating conditions when the fault was set.
2. Visual Inspection:
   • Begin with a thorough visual inspection of the glow plug wiring harness and connectors for Bank #1. Look for signs of damage, fraying, burnt wires, loose connections, or corrosion.
   • Inspect the Glow Plug Control Module (GPCM) and its connectors for any visible damage or corrosion.
   • Check the fuse box for any blown fuses related to the glow plug circuit. Refer to the vehicle’s service manual for fuse locations and ratings.
3. Glow Plug Resistance Test (Individual Plugs):
   • With the engine cold and ignition OFF, carefully disconnect the electrical connector from each glow plug on Bank #1.
   • Using a DMM set to the ohms scale, measure the resistance between the terminal of each glow plug and a good engine ground (or battery negative terminal).
   • Compare the readings to manufacturer specifications, which are typically very low, often between 0.1 to 2.0 ohms. An “OL” (open line) or infinite resistance indicates an open circuit, meaning a faulty glow plug. Readings significantly higher than specifications also indicate a faulty glow plug. All glow plugs on the bank should ideally have similar readings.
4. Glow Plug Power Supply Test:
   • Reconnect the glow plug harness to the GPCM.
   • Using a DMM set to the voltage scale, back-probe the glow plug harness connector for each glow plug on Bank #1. Alternatively, if accessible, measure at the glow plug terminal with the harness connected.
   • Have an assistant activate the glow plugs (e.g., by turning the key to the ON position, but not starting, or using a bi-directional scan tool function to command the glow plugs ON).
   • You should observe battery voltage (approximately 12V) at each glow plug terminal for the duration of the glow plug cycle (typically 5-15 seconds, depending on temperature). No voltage indicates a fault in the GPCM, its power supply, or the wiring from the GPCM.
5. GPCM Power and Ground Test:
   • Locate the main power and ground supply wires to the GPCM.
   • Verify constant battery voltage at the main power input terminal(s) of the GPCM with the key ON.
   • Verify a strong ground connection at the GPCM’s ground terminal(s) using the DMM’s continuity or resistance function to chassis ground.
6. Wiring Integrity Test (GPCM to Glow Plugs):
   • If no power is reaching the glow plugs but the GPCM has power and ground, disconnect the harness from both the GPCM and the glow plugs.
   • Perform a continuity test on each wire between the GPCM connector and the corresponding glow plug connector on Bank #1. Resistance should be very low (close to 0 ohms).
   • Also, check each wire for shorts to ground and shorts to power.
7. Scan Tool Bi-directional Control: If available, use a professional scan tool to command the glow plugs ON and monitor their operation in live data (if the vehicle supports glow plug current monitoring). This can help confirm GPCM functionality and individual glow plug current draw.

Recommended Repairs and Solutions

Once the diagnostic steps have isolated the fault, the following repairs are typically recommended:

• Replace Faulty Glow Plugs: If individual glow plugs on Bank #1 fail the resistance test, they should be replaced. It is often recommended to replace all glow plugs on Bank #1, or even all glow plugs in the engine, especially on higher mileage vehicles, as the remaining plugs may soon fail as well.
• Replace Glow Plug Control Module (GPCM) or Relay: If the GPCM is determined to be faulty (e.g., not supplying power, internal monitoring failure) and all wiring and glow plugs are confirmed good. Ensure the new module is correctly programmed or configured if required by the vehicle manufacturer.
• Repair or Replace Wiring Harness: Address any damaged, corroded, or open circuits in the wiring leading to the glow plugs or the GPCM. Use appropriate connectors and heat shrink tubing for durable repairs.
• Replace Blown Fuse: If a fuse was found to be blown, replace it with a fuse of the correct amperage rating. Investigate the cause of the blown fuse, as it might indicate an underlying short circuit.
• Clean Corroded Terminals: Thoroughly clean any corroded electrical terminals on glow plugs, GPCM, or harness connectors to ensure proper electrical contact. Applying dielectric grease after cleaning can help prevent future corrosion.
• ECM/PCM Reprogramming or Replacement: In rare cases, if all other components are verified to be in good working order, the ECM/PCM itself may be at fault. A software update or replacement might be necessary. This should be a last resort after exhaustive component and wiring checks.

Mechanic’s Tips:

• When replacing glow plugs, be extremely careful as they can be fragile and seize in the cylinder head. Always ensure the engine is at operating temperature when attempting removal to minimize the risk of breakage. Use penetrating oil and allow it to soak.
• Always torque glow plugs to the manufacturer’s specified value to prevent damage to the cylinder head or the new glow plug. Over-tightening can cause damage, and under-tightening can lead to compression leaks.
• Consider using anti-seize compound on the glow plug threads, but only if recommended by the glow plug or vehicle manufacturer, as some glow plugs are designed to be installed dry.
• After any repair, clear the fault codes with an OBD-II scanner and perform a test drive to ensure the repair is successful and the P1395 code does not return. Monitor live data if available to confirm proper glow plug operation.