| Vehicle Type | Meaning of P1456 |
|---|---|
| Diesel (Opel, VW, Audi) | Exhaust Gas Temperature (EGT) Sensor 2 Circuit Malfunction |
| Honda / Acura | EVAP Control System Leakage (Fuel Tank Area) |
| Nissan | EVAP Control System Very Small Leak |
The P1456 fault code is one of the most confusing codes for car owners because its meaning changes entirely depending on what car you drive. If you are driving a modern diesel car, it's likely a critical sensor issue stopping your DPF from cleaning. If you drive a Honda, it might just be a loose gas cap.
This comprehensive guide will cover both scenarios, helping you diagnose the issue correctly without wasting money on the wrong parts.
Scenario A: The Diesel Particulate Filter Issue (Opel, Vauxhall, VW)
If you have been following our series on DPF faults, you already know about Code P1453 (Pressure Sensor) and Code P1454 (Temperature Sensor 1).
Code P1456 completes this puzzle. It usually refers to the Exhaust Gas Temperature Sensor 2. This sensor is typically located after the Diesel Particulate Filter (DPF).
Why do I need two temperature sensors?
Your Engine Control Unit (ECU) relies on a "Before" and "After" picture. By comparing the temperature coming into the filter (Sensor 1/P1454) versus the temperature leaving the filter (Sensor 2/P1456), the car can monitor the efficiency of the regeneration process. If Sensor 2 fails or reports erratic data, the ECU aborts the cleaning cycle to prevent overheating.
Symptoms of Diesel P1456:
- Limp Mode: Limited RPMs to protect the exhaust system.
- Regeneration Failure: The car refuses to burn off soot.
- Code Persistence: The code returns immediately after clearing if the circuit is broken.
The Fix (Diesel):
Check the wiring loom near the rear of the engine bay. Because this sensor is further down the exhaust line, its wiring often rubs against the chassis or axle. If the wiring is intact, replace the EGT Sensor 2.
Scenario B: The EVAP Leak (Honda, Acura, Nissan)
If you are driving a petrol Honda Civic, Accord, CR-V, or Odyssey, P1456 has nothing to do with exhaust temperature. Instead, it indicates a leak in the Evaporative Emission Control System (EVAP), specifically on the fuel tank side.
Common Causes for Honda P1456:
- Loose Gas Cap: The most common cause (90% of cases). If the cap doesn't click or the seal is dry-rotted, vapors escape.
- Two-Way Valve (Bypass Solenoid): A small valve near the fuel tank that can get stuck open.
- Rusted Fuel Filler Neck: In snowy states, salt can rust the pipe where you insert the gas nozzle, preventing a good seal.
🔧 How to Diagnose Like a Pro
Whether you have the Diesel issue or the Honda EVAP issue, you need a scanner that can read Manufacturer Specific Data. A cheap $20 dongle might only show "Manufacturer Control."
Using a tool like the iCarsoft CR Ultra P allows you to:
- For Diesels: View the live temperature of EGT Sensor 2 in real-time (should move between 200°C - 600°C).
- For Hondas: Perform an "EVAP System Test" (Bi-directional control) to seal the vent valve and check if the tank holds pressure.
Summary: Diagnosis Checklist
Follow these steps to clear P1456:
- Step 1: Check your car model. Is it a Diesel (Europe/Domestic) or a Petrol (Asian)?
- Step 2 (Honda): Tighten your gas cap and clear the code. Drive for 50 miles. If it returns, check the fuel filler neck for rust.
- Step 3 (Diesel): Inspect the wiring to the post-DPF sensor. If wiring is good, use a scanner to check Live Data. If the sensor reads -40°C or static, replace the sensor.
- Step 4 (Verify): Always perform a drive cycle after repair to ensure the monitors reset.
Frequently Asked Questions
Is P1456 dangerous to drive with?
For Honda owners (EVAP), no. It simply means you are polluting slightly more than usual. For Diesel owners (DPF), yes. You should fix it immediately because it prevents DPF regeneration, which can destroy your engine's exhaust system.
Can a bad gas cap cause P1456?
Yes, specifically on Honda and Acura vehicles. It is the number one cause. Try tightening it or replacing it with an OEM cap before visiting a mechanic.
How much does it cost to fix P1456?
A gas cap costs around $20. An Exhaust Gas Temperature sensor (for diesels) typically costs between $80 and $150, plus labor.
