P1396

What Does Code P1396 Mean?

DTC P1396 signifies a “Glow Plug Monitor Fault (Bank #2)”. This code is specific to diesel engines, which utilize glow plugs to pre-heat the combustion chambers, facilitating ignition, particularly during cold start conditions. The Engine Control Module (ECM), also commonly referred to as the Powertrain Control Module (PCM), is responsible for monitoring the operational status and electrical integrity of the glow plug circuits. When P1396 is set, the ECM has detected an electrical anomaly within the glow plug circuit for Bank 2. In V-configuration engines (V6, V8, etc.), Bank 2 refers to the cylinder bank that does not contain cylinder #1. The ECM typically monitors parameters such as current draw, resistance, or voltage drop across the glow plugs or the glow plug control module/relay to ensure they are functioning within specified parameters. A “monitor fault” indicates that the ECM is not receiving the expected feedback from Bank 2’s glow plug circuit, suggesting issues like an open circuit, short circuit, excessive resistance, or insufficient current draw, preventing proper glow plug operation on that bank.

Common Symptoms

• Hard Start or No Start Condition in Cold Weather: This is the most prevalent symptom, as glow plugs are crucial for igniting diesel fuel when ambient temperatures are low.
• Rough Idle and Hesitation After Cold Start: Incomplete combustion due to inadequate pre-heating can lead to an uneven running engine until it warms up.
• Increased White or Blue Exhaust Smoke on Cold Start: Unburned or partially burned fuel from cold cylinders will result in visible smoke.
• Illumination of the Check Engine Light (CEL): The primary indicator for any OBD-II related fault.
• Reduced Engine Performance During Warm-Up Phase: While less common, the engine might exhibit reduced power or responsiveness until it reaches operating temperature.

What Causes the Code P1396?

• Faulty Glow Plug(s) on Bank 2: An open circuit, internal short circuit, or excessive resistance within one or more glow plugs on Bank 2 is a very common cause.
• Defective Glow Plug Control Module or Relay: The module or relay responsible for supplying and controlling power to the glow plugs on Bank 2 may be internally faulty, preventing proper voltage supply or monitoring.
• Wiring Harness Issues: Damage, chafing, corrosion, or an open/short circuit within the wiring harness connecting the ECM/PCM, glow plug control module, and the glow plugs on Bank 2.
• Corroded Electrical Connectors: High resistance caused by corrosion at the electrical connectors to the glow plugs or the glow plug control module.
• ECM/PCM Failure: Although rare, an internal fault within the ECM/PCM’s glow plug monitoring circuit can trigger this code.

How to Diagnose and Troubleshoot

Diagnosis of P1396 requires a systematic approach using a digital multimeter (DMM) and an OBD-II scan tool.

1. Retrieve and Document Freeze Frame Data: Connect an OBD-II scan tool to retrieve the P1396 code and any associated freeze frame data. Note engine parameters at the time the code was set, such as engine temperature. Check for any other related codes (e.g., specific P067x codes for individual glow plugs).
2. Visual Inspection: Perform a thorough visual inspection of the glow plugs, their wiring harnesses, and connectors on Bank 2. Look for signs of physical damage, chafing, corrosion, burning, or loose connections. Verify the battery terminals are clean and tight, and battery voltage is adequate (typically 12.6V or higher with the engine off).
3. Glow Plug Resistance Test (Individual Glow Plugs):

• Disconnect the electrical connector from each glow plug on Bank 2.
• Set your DMM to the lowest resistance (Ohms) scale.
• Connect one DMM lead to the glow plug terminal and the other to a clean engine ground.
• A healthy glow plug will typically show very low resistance, usually between 0.1 and 1.5 Ohms, depending on the manufacturer’s specification. An “OL” (open circuit) reading indicates a failed glow plug. Significant deviation from the specified resistance (e.g., very high resistance) also indicates a fault.

Glow Plug Voltage Supply Test:

• Reconnect the glow plug connectors.
• Access the glow plug control module/relay for Bank 2.
• Using the scan tool, attempt to activate the glow plugs (if possible) or initiate a cold start.
• While the glow plugs are commanded on, use the DMM to measure voltage at the glow plug harness connector for Bank 2. Compare to battery voltage. A significantly lower voltage or no voltage indicates an issue with the control module or wiring.

Glow Plug Control Module/Relay Test:

• With the engine cold, verify the control module is receiving proper power and ground inputs when commanded by the ECM (refer to manufacturer wiring diagrams for specific pinouts).
• Test the output voltage from the control module to Bank 2 glow plugs during the glow cycle. If input power is present but no output power to Bank 2 is observed, the module is likely faulty.

Wiring Harness Continuity and Short Circuit Test:

• Disconnect the glow plug control module and the glow plugs on Bank 2.
• Use the DMM to check for continuity in the glow plug circuit wires from the control module connector to the glow plug connectors. Look for open circuits.
• Also, check for shorts to ground or shorts to power in the wiring harness.

Recommended Repairs and Solutions

Once the diagnostic steps have identified the root cause of P1396, the following repairs are commonly performed:

• Replace Faulty Glow Plug(s): If resistance tests confirm specific glow plugs on Bank 2 are faulty, replace them. It is often recommended to replace all glow plugs on the affected bank, or even all glow plugs across the engine, especially on high-mileage vehicles, to ensure balanced operation and prevent future failures. Always use high-quality, OEM-spec replacement glow plugs.
• Repair or Replace Wiring and Connectors: If the wiring harness or electrical connectors are found to be damaged, corroded, or have open/short circuits, repair or replace them as necessary. Ensure all connections are clean and secure.
• Replace Glow Plug Control Module/Relay: If diagnostics definitively point to the glow plug control module or relay as the cause for the Bank 2 malfunction, replace the unit. Ensure the new module is correctly programmed or adapted if required by the vehicle manufacturer.
• ECM/PCM Replacement/Reprogramming: This is a very rare solution and should only be considered after all other potential causes have been thoroughly investigated and ruled out. If an ECM/PCM is replaced, it will require specific programming and calibration to the vehicle.
• Post-Repair Verification: After any repair, clear the DTCs with the OBD-II scanner. Perform several cold start cycles and monitor glow plug operation (if visible in live data). Rescan the vehicle for any pending or stored codes to confirm the repair has been successful and P1396 does not return.