Dodge Ram P0456: Common Causes and Solutions

Dodge Ram P0456: Causes, Diagnosis, and Repair Guide

A Dodge Ram P0456 code is a common issue that can trigger a Malfunction Indicator Light (MIL) and often comes with a “loose fuel cap” warning on the dash. A P0456 code indicates a small leak in the evaporative emissions (EVAP) system, which is why the dash tells you to check for a loose fuel cap. If left unresolved, it can lead to reduced fuel efficiency and increased emissions.

In this article, I’ll break down what a P0456 code means, how the EVAP system works in a Dodge Ram, the most common causes of this issue in Chrysler vehicles, and a real-world case study of how a technician diagnosed and repaired the problem.

What is a P0456 Code?

The P0456 code is a generic OBD-II trouble code that stands for: “Evaporative Emissions System Small Leak Detected.”

This code is set when the Powertrain Control Module (PCM) detects a minor vacuum leak in the EVAP system. The EVAP system prevents fuel vapors from escaping into the atmosphere by storing them in a charcoal canister and eventually sending them to the engine to be burned.

A P0456 code differs from P0455 (large leak detected) and P0442 (medium leak detected)—indicating that the leak is very small, often as tiny as 0.020 inches in diameter.

How the EVAP System Works in a Dodge Ram

The EVAP system in a Dodge Ram is designed to prevent fuel vapors from escaping into the environment. It consists of several key components:

• Fuel Tank Pressure Sensor (FTPS) – Monitors vacuum and pressure changes in the fuel tank.
• Charcoal Canister – Stores fuel vapors before they are purged into the engine.
• Purge Valve (Purge Solenoid) – Controls when stored vapors enter the engine.
• Evaporative System Integrity Monitor (ESIM) – A natural vacuum leak detection system that replaces older LDP (Leak Detection Pump) designs.
• Fuel Cap – Seals the fuel system and prevents vapors from escaping.

How the ESIM Works

Unlike traditional vacuum pumps, Chrysler

ESIM Switch

products use an Evaporative System Integrity Monitor (ESIM). It is a passive system that relies on natural pressure changes. When the engine is off and cooling, the fuel system generates a vacuum. The ESIM has a weighted check valve that closes when the vacuum reaches a threshold, allowing the PCM to confirm the system is sealed.

If the ESIM fails to close, the Dodge Ram P0456 code may be set, indicating a small leak.

Common Causes of a Dodge Ram P0456 Code

The most frequent causes of P0456 in Chrysler vehicles include:

• Faulty ESIM (Evaporative System Integrity Monitor) – If the ESIM valve does not properly close, the PCM detects a leak. (High failure rate item)
• Loose or Faulty Fuel Cap – The most common and simplest issue. An improperly sealed fuel cap can trigger a small EVAP leak.
• Leaking EVAP Hoses – Cracked or disconnected vacuum hoses can cause small leaks.
• Damaged Charcoal Canister – A cracked canister can allow vapors to escape.
• Defective Purge Valve – If the purge valve does not seal correctly, it can create a leak in the system.
• Wiring Issues – Faulty wiring or a broken ground in the ESIM circuit can cause the PCM to misread system status.

Now, let’s examine how one technician diagnosed and fixed a Dodge Ram P0456 issue in the real world.

Case Study: Diagnosing and Repairing a Dodge Ram P0456 Code

A customer brought in a 2014 Dodge Ram after noticing the MIL light on and a loose fuel cap message on the dashboard.

Step 1: Scanning for Codes— The technician connected an OBD-II scan tool and found DTC P0456 – EVAP System Small Leak Detected. Since a loose fuel cap can often cause this, he replaced the fuel cap with an OEM part and attempted to clear the code. However, the code would not reset.

Step 2: Smoke Testing the EVAP System— To locate a leak, the technician performed a smoke test on the entire EVAP system. This test pressurizes the system with smoke, revealing leaks. However, no visible leaks were found.

Step 3: Checking ESIM Operation— With the scan tool connected, he monitored the ESIM valve. The fuel tank pressure sensor (FTPS) detected a strong vacuum, but the ESIM never showed “closed.”

To verify the ESIM’s function, he jumped the ESIM connector manually, and the scan tool displayed “open”—confirming that the ESIM was not responding properly.

Step 4: Testing the Wiring Circuit— The technician then performed a resistance test at pin #70 in the PCM plug C1, which should have shown continuity to the ESIM. Instead, it displayed infinite resistance, meaning a broken wire was in the circuit.

Using a power probe, he checked the integrity of the power and ground wires. This led to the discovery of a crushed/broken signal wire in the wiring harness mounted to the frame near the driver-side exhaust manifold.

Step 5: Repairing the Wiring Issue— He repaired the broken signal wire, ensuring continuity was restored.

Step 6: Clearing the Code and Verifying the Repair— After repairing the wiring, he cleared the DTC using the scan tool. The ESIM now read “closed,” confirming the fix.

To ensure the problem was fully resolved, he performed a drive cycle to complete the EVAP readiness monitor, confirming that the Dodge Ram P0456 code was fixed.

Take Aways From This Article

A Dodge Ram P0456 code can be frustrating because it indicates a very small leak, making it difficult to locate. While a loose gas cap can be the cause, the most common faults are the ESIM, associated wiring, damaged hoses, or purge valve issues.

In this case, a broken signal wire prevented the EVAP system from reporting a sealed condition, falsely triggering P0456. A thorough diagnosis, including a scan tool check, smoke test, and wiring inspection, led to the correct repair.

If you’re dealing with a Dodge Ram P0456 code, follow these diagnostic steps and don’t overlook potential wiring issues in the circuit. Proper troubleshooting will save time and prevent unnecessary part replacements.

©, 2025 Rick Muscoplat