Subaru Code P1402: Understanding and Fixing the EGT Sensor Problem

The check engine light in your Subaru has come on, and the diagnostic shows trouble code P1402 Subaru. Don’t panic. This code is specific to models from the Japanese manufacturer and is often related to the emissions control system. It typically points to a malfunction in the Exhaust Gas Temperature (EGT) sensor circuit. Understanding this code, its causes, and possible solutions is essential to get your vehicle back into optimal running condition and avoid costly repairs. This article guides you step-by-step through diagnosing and resolving the P1402 issue on your Subaru.

What is the P1402 Trouble Code on a Subaru?

Code P1402 is a generic manufacturer code, meaning it is specific to Subaru. It translates to “Exhaust Gas Temperature (EGT) Sensor Circuit – Low Input.” As the name suggests, this code is triggered when the engine control unit (ECU) detects an abnormally low voltage coming from the EGT sensor.

The role of this sensor, usually located in the exhaust manifold or just before the turbocharger, is crucial. It monitors the exhaust gas temperature to protect sensitive components, such as the turbocharger and catalytic converter, from destructive overheating. If the reading is incorrect, the ECU may activate a limp mode to protect the engine, which often results in a noticeable loss of power.

Symptoms Associated with Code P1402

When the P1402 Subaru code is stored in the ECU, several symptoms may appear, either alone or in combination:

• The “Check Engine” light illuminates: This is the most obvious sign.
• Loss of engine power: The vehicle lacks acceleration and seems “choked.”
• Limited engine RPM: The ECU may cap the engine RPM, for example, at 2500-3000 RPM, to prevent any risk of overheating.
• Increased fuel consumption: The limp mode disrupts the air-fuel mixture.
• Irregular idle: The engine may misfire or have an unstable idle.

Main Causes of the P1402 Fault

Several issues can cause a P1402 code. It is important to investigate them in a logical order, from simplest to most complex.

• A faulty EGT sensor: This is the most common cause. Like any sensor, it has a limited lifespan and can fail.
• Damaged wires or corroded connector: The wires connecting the sensor to the ECU can be cut, chafed, burned, or simply poorly connected. Corrosion on the connectors is also a common cause.
• A problem with the engine control unit (ECU): Although rarer, the ECU itself can be faulty and send or interpret signals incorrectly.
• A defective electrical circuit: This could be a bad ground connection or a break in the wiring harness.

Diagnosis and Solutions for Fixing Code P1402

Before replacing expensive parts, a methodical diagnosis is essential.

1. Visual Inspection

Start with a thorough visual inspection. Locate the EGT sensor (often on the driver’s side exhaust manifold). Examine the connector: is it properly plugged in, clean, and free of corrosion? Follow the wires along their entire length to check that they are not burned, cut, or rubbing against a moving part.

2. Electrical Testing of the EGT Sensor

Using a multimeter, you can measure the sensor’s resistance. The exact value varies by model and temperature, but it is generally between 50 and 200 kΩ when cold. An infinite resistance (open circuit) or zero resistance (short circuit) indicates a faulty sensor. Consult your Subaru repair manual for the specific value.

3. Checking the Signal and Power Supply

A more advanced test involves checking the signal voltage sent to the ECU with the ignition on. If the sensor is receiving its power supply (usually 5V) but returns a constantly low signal (close to 0V), this confirms the fault.

4. Replacing the EGT Sensor

If your tests confirm the sensor is faulty, replacing it is the solution. Plan on using a quality OEM sensor or a good quality aftermarket one. This task is within the reach of a skilled DIYer, but access can be difficult depending on the model. Remember to always disconnect the battery before any work and let the engine cool down completely.

Conclusion

The P1402 Subaru code, while concerning, is often resolved by replacing a faulty EGT sensor or repairing a simple wiring issue. An accurate diagnosis will save you from changing parts unnecessarily. If you don’t feel comfortable performing these tasks, don’t hesitate to entrust your vehicle to a professional mechanic, preferably a Subaru specialist, who will have the tools and technical knowledge to fix the problem effectively and ensure the longevity of your engine.