P1393 Code? Here’s How to Fix It – Quickly and Easily

P1393 is a manufacturer-specific OBD-II diagnostic trouble code. Its exact definition depends on the vehicle application, but it generally relates to a fault in a glow plug circuit or an ignition system monitor.

Because definitions vary by manufacturer, the exact diagnostic path requires verifying your specific vehicle’s factory service information. The code identifies a detected condition, not necessarily a failed part.

Key Takeaways

• P1393 is a manufacturer-specific code indicating a fault in a glow plug circuit, ignition monitor, or related sensor.
• Possible causes include damaged wiring, failed glow plugs, or internal control module issues.
• Symptoms may include hard starting in cold weather, rough idling, and an illuminated check engine light.
• Diagnosis requires verifying the exact factory definition and testing the relevant circuits.

P1393 Code Description and Implications

P1393 is a manufacturer-specific code, meaning its exact definition varies by automaker. The powertrain control module uses this code to flag an anomaly within the ignition or cold-start system.

Some VW and Audi applications: P1393 typically indicates an electrical malfunction in the glow plug circuit for Bank 2. On inline engines, this often refers to the glow plugs for specific cylinders, such as cylinders 3 and 4.

Certain Ford Powerstroke applications: This code may indicate a fault in the glow plug monitor circuit for a specific cylinder, such as cylinder 3, preventing the module from verifying glow plug operation.

Because the code is manufacturer-specific, you must verify the exact factory definition for your vehicle before beginning diagnosis. The specific fault code meaning dictates the test.

Common Causes of the P1393 Code

Wiring and connector damage: The glow plug harness routes near the engine block and is exposed to extreme heat and vibration. Chafed wires or corroded pins can interrupt the control signals.

Component failure: One or more glow plugs may fail internally, creating an open circuit that the control module detects during the pre-start self-test.

Control module or relay issues: A faulty glow plug relay or an internal fault within the engine control module can prevent the system from delivering power to the circuit.

Symptoms Associated With P1393

Because glow plugs are primarily used for cold starts, a P1393 fault may not cause noticeable drivability concerns once the engine is warm.

During cold weather, you may experience extended cranking times, hard starting, or rough idling until the combustion chambers reach operating temperature.

You will see an illuminated check engine light. On diesel applications, a glow plug warning indicator may also appear on the instrument cluster.

Diagnosing the P1393 Trouble Code

Diagnosis must begin by confirming the exact factory definition and wiring diagram for your specific make, model, and year. Retrieve freeze frame data to understand the conditions when the code set.

Inspect the glow plug wiring harness and connectors for physical damage, heat exposure, or corrosion. Repair any visible wiring damage before proceeding to electrical tests.

Use a multimeter to measure the resistance of each glow plug identified by the factory service information. Compare your readings against the manufacturer’s specifications to identify an open or shorted plug.

Repairing the P1393 Issue

Repairs must follow confirmed diagnostic testing. Do not replace the glow plugs without verifying the wiring harness and relay first.

If wiring damage or connector corrosion is found, repair or replace the affected harness sections. Ensure all repairs are properly sealed against moisture and heat.

If a specific glow plug fails resistance testing, replace it with a component meeting the exact vehicle specification. On many diesel engines, replacing all glow plugs at the same time is recommended if one has failed.

Cost Considerations for P1393 Repairs

Repair costs depend on the confirmed root cause, component accessibility, and local labor rates. Replacing an externally accessible glow plug is generally a straightforward procedure.

If the glow plugs are difficult to access or require intake manifold removal, labor time will increase significantly. Always factor in the cost of proper diagnostic time.

Prevention Strategies for Future Occurrences

Inspecting the glow plug wiring harness during routine maintenance can help identify developing insulation damage before it causes a circuit fault.

Using the correct glow plugs and avoiding excessive use of starting fluid can help prevent internal glow plug damage and premature failure.

Troubleshooting Tips and Best Practices

Always verify the exact definition of P1393 for your specific vehicle. Assuming it is always a failed glow plug can lead to misdiagnosis when a simple wiring issue or bad relay is the actual cause.

Do not ignore the glow plug relay. On many applications, a single relay controls multiple glow plugs, and a failed relay can mimic a circuit fault for an entire bank.

Check for related codes that might point to a systemic issue, such as a failing alternator or a shared ground circuit problem.

More OBD-II Codes

Frequently Asked Questions

Is P1393 a generic or manufacturer-specific code?

P1393 is a manufacturer-specific code. Its exact definition and diagnostic procedure vary depending on the vehicle make, model, and year. Always consult the factory service information for your specific application.

Can a bad glow plug relay cause a P1393 code?

Yes. The glow plug relay supplies power to the glow plugs. If the relay fails or its control circuit malfunctions, the module will detect a lack of voltage and may set a bank-specific code.

Is it safe to drive with a P1393 code?

The vehicle is generally safe to drive once warm, as glow plugs are primarily used for cold starts. However, you may experience hard starting in cold weather and will fail an emissions inspection.

Will replacing the glow plugs always fix P1393?

Not always. P1393 indicates a circuit or monitor fault. The root cause could be damaged wiring, a corroded connector, or a failed relay. Proper electrical testing is required to confirm the root cause.

Do I need to replace all the glow plugs if one is bad?

While the code identifies a specific bank or cylinder, it is often recommended to replace all glow plugs simultaneously on high-mileage diesel engines to prevent subsequent failures and avoid repeating the labor.

What Should You Do About the P1393 Code?

Confirm the exact factory definition and wiring diagram for your specific vehicle application. Inspect the relevant glow plug circuits, relays, and connectors for physical damage or heat exposure.

Perform targeted electrical testing on the relevant system and components to isolate the fault. Repair the confirmed root cause, then verify the repair by clearing the codes and monitoring live data.