The P1394 diagnostic trouble code is a manufacturer-specific powertrain code. Its exact definition depends heavily on the vehicle make, pointing to an ignition coil output stage fault, a glow plug circuit issue, or a G-sensor circuit malfunction.
Because this code targets entirely different systems across manufacturers, the exact vehicle application must be verified before diagnosis. The code alone does not prove a specific component has failed without proper testing.
Quick Navigation
Key Takeaways
- P1394 is a manufacturer-specific powertrain code with differing definitions depending on the vehicle make.
- On Volkswagen and Audi applications, it indicates an Ignition Coil Power Output Stage 2 Malfunction.
- On Ford, Mazda, and Nissan diesel applications, it points to a Glow Plug Circuit High Input fault on Bank 2.
- On Honda, Isuzu, and GM applications, it indicates a G-Sensor or Wheel Speed Sensor 1 Circuit Intermittent fault.
- Diagnosis requires verifying the exact factory definition and testing the relevant ignition, glow plug, or G-sensor circuit.
P1394 Code Description and Implications
The P1394 code indicates that a control module has detected a specific fault within the ignition, starting, or stability systems. Because it is a manufacturer-specific code, the exact monitored component varies significantly by brand.
Some Volkswagen and Audi applications: P1394 indicates an Ignition Coil Power Output Stage 2 Malfunction. The ECM detects an electrical issue in the secondary output stage of the ignition coil pack or module.
Certain Ford, Mazda, and Nissan diesel applications: The code indicates a Glow Plug Circuit High Input fault on Bank 2. The PCM detects that the voltage in the glow plug heater circuit for the second bank of cylinders is higher than expected.
Some Honda, Isuzu, and GM applications: P1394 indicates a G-Sensor Intermittent Voltage High or Wheel Speed Sensor 1 G-Sensor Circuit Intermittent fault. The control module detects an erratic signal from the lateral acceleration sensor.
Common Causes of the P1394 Code
Because P1394 applies to different systems across different brands, the root cause depends on the verified vehicle application.
Volkswagen and Audi Causes: A failed ignition coil pack or output stage module, damaged wiring or poor electrical connections at the coil, or an internal ECM driver issue.
Ford, Mazda, and Nissan Diesel Causes: A faulty glow plug relay, damaged wiring or poor connections in the Bank 2 glow plug circuit, or a failed glow plug.
Honda, Isuzu, and GM Causes: A faulty G-sensor, damaged wiring harness, poor electrical connections, or sensor mounting issues causing intermittent signal loss.
Symptoms Associated With P1394
When the control module detects a critical system fault, it illuminates a warning light and may alter vehicle operation.
Warning Lights: The Check Engine Light will illuminate. On VW and Audi applications, misfires may cause the light to flash. On Honda and GM applications, a Traction Control or ABS warning light may also appear.
Drivability: On VW and Audi applications, engine misfires, rough idling, hesitation, or reduced power may occur. On diesel applications, hard starting in cold weather is possible. On Honda and GM applications, the traction or stability control systems may disable themselves.
Diagnosing the P1394 Trouble Code
Accurate diagnosis begins by verifying the exact vehicle application and reviewing manufacturer-specific service information.
For Volkswagen and Audi applications: Inspect the wiring harness and connectors for the ignition coil output stage. Test the coil’s primary and secondary resistance and verify the control signal from the ECM.
For Ford, Mazda, and Nissan diesel applications: Inspect the wiring harness and glow plug relay for Bank 2. Verify power and ground at the relay and test the resistance of the individual glow plugs.
For Honda, Isuzu, and GM applications: Inspect the wiring harness and connectors for the G-sensor. Verify the sensor reference voltage, signal circuit, and ground according to the manufacturer procedure. Check the sensor mounting and inspect for physical damage.
Repairing the P1394 Issue
Repairs must follow the confirmed root cause identified during diagnosis.
Ignition Component Repairs: If an ignition coil or output stage module fails testing, replace the confirmed failed component. Repair any damaged wiring or corroded connectors in the ignition circuit.
Glow Plug Repairs: If a glow plug or relay fails testing, replace the confirmed failed component. Repair any damaged wiring in the glow plug circuit and verify proper cold-start operation.
G-Sensor Repairs: If the G-sensor fails electrical testing or shows intermittent signal loss, replace the sensor. Repair any damaged wiring and ensure the new sensor is mounted securely and calibrated if required.
Cost Considerations for P1394 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Replacing an external ignition coil or glow plug relay involves minimal to moderate labor. However, accessing glow plugs buried under the intake manifold or replacing and calibrating a G-sensor requires additional labor time and specialized equipment.
Prevention Strategies for Future Occurrences
Ensuring electrical connectors and sensor mounts are kept clean and secure helps prevent moisture intrusion, corrosion, and intermittent signal loss.
Keeping the engine bay clean and ensuring wiring harnesses are properly secured away from hot exhaust components helps prevent insulation damage and short circuits in ignition and sensor circuits.
Troubleshooting Tips and Best Practices
Follow these practices to avoid misdiagnosis and ensure accurate repairs.
Do not assume the ignition coil is dead on VW applications: A broken wire or corroded connector in the output stage circuit is a frequent cause of the fault. Always verify circuit integrity before replacing the coil pack.
Check for related codes: Look for accompanying misfire codes on VW applications, or ABS and traction control codes on Honda and GM applications, which might help pinpoint a broader wiring harness issue.
Verify your definition: When researching this fault code, always confirm whether your specific vehicle uses the ignition coil, glow plug, or G-sensor definition before ordering parts.
More OBD-II Codes
| P1390 | P1371 | P1370 | P1368 |
| P1367 | P1366 | P1395 | P1396 |
| P1398 | P1399 | P1405 | P1406 |
| P0300 | P0301 | P1365 | P1364 |
| P1324 | P1323 | P1322 | P1321 |
| P1320 | P1315 | P1359 | P1353 |
Frequently Asked Questions
Is P1394 a generic or manufacturer-specific code?
No. P1394 is a manufacturer-specific powertrain code. Its definition varies significantly by brand, indicating an ignition output stage fault, a glow plug circuit issue, or a G-sensor malfunction.
Can I drive my vehicle with a P1394 code?
The vehicle may remain drivable, but an ignition or glow plug fault can cause misfires and hard starting, while a G-sensor fault will disable traction and stability control systems.
Will disconnecting the battery clear the P1394 code?
Disconnecting the battery might temporarily clear the code. However, it does not repair the underlying failed coil, damaged wiring, or faulty sensor, and the code will return upon the next monitor cycle.
Can a bad G-sensor cause a P1394 code?
Yes. On Honda, Isuzu, and GM applications where P1394 indicates a G-sensor circuit intermittent fault, a failed lateral acceleration sensor is a primary cause of the code.
Does P1394 affect the transmission?
No. The P1394 code relates strictly to the engine ignition system, diesel glow plugs, or chassis G-sensor. It does not directly affect the automatic or manual transmission operation.
What Should You Do About the P1394 Code?
When a P1394 code appears, confirm the exact factory definition for your specific vehicle make and model. Because this code targets entirely different ignition, starting, and stability systems depending on the manufacturer, applying the wrong diagnostic path will lead to misdiagnosis.
Follow the applicable manufacturer diagnostic procedure to test the relevant system and components. Once the root cause is confirmed, complete the necessary electrical repairs, component replacements, or sensor corrections before returning the vehicle to normal service.
