P1405 Mercury Fault Code: Diagnosis and Solutions for the EGR Sensor

The check engine light on your Mercury has come on, and the diagnostic scanner indicates the fault code P1405 Mercury. This code, specific to Ford group vehicles (including Mercury), points to a malfunction in the Exhaust Gas Recirculation (EGR) system. Ignoring it can lead to performance loss, increased fuel consumption, and even more serious damage. This article guides you through understanding the causes, performing a diagnosis, and finding solutions to effectively resolve the P1405 Mercury problem.

What is the P1405 Code on a Mercury?

The fault code P1405 is defined as “Differential Pressure Feedback EGR Sensor Circuit.” In simpler terms, the Powertrain Control Module (PCM) detects a problem with the sensor that measures EGR gas flow. This crucial sensor, also called the DPFE sensor (Differential Pressure Feedback EGR), informs the computer about the actual amount of gas being recirculated. An incorrect or missing signal from this sensor triggers the P1405 Mercury code.

Symptoms of the P1405 Fault

Several warning signs typically accompany the appearance of this code:

• Illuminated Check Engine Light: This is the most obvious sign.
• Irregular or Rough Idle: The engine may stall at idle or have hiccups.
• Noticeable Power Loss: Especially during acceleration.
• Increased Fuel Consumption: The engine runs less efficiently.
• Higher Pollutant Emissions: Potential failure in emissions testing.

Main Causes of the P1405 Mercury Code

Several components can be the source of this fault. Here are the most common causes, in order of likelihood:

• A Faulty DPFE Sensor: This is the most common cause. The sensor itself is defective and sends inconsistent values to the PCM.
• Clogged or Deteriorated DPFE Sensor Hoses: The small rubber hoses connecting the sensor to the EGR system can become clogged with carbon deposits, crack, or come loose, distorting the pressure reading.
• Electrical Problems: An oxidized, loose connector, or damaged electrical wires (cut, chafed) between the sensor and the computer.
• A Clogged EGR Valve: If the EGR valve itself is clogged with carbon, the gas flow is blocked, which the DPFE sensor cannot measure correctly.
• A Problem with the PCM: Although rare, an internal failure of the Powertrain Control Module is a possibility.

Step-by-Step Diagnosis and Troubleshooting

Before replacing expensive parts, it is essential to perform a methodical check.

1. Visual Inspection

Start by locating the DPFE sensor (usually mounted on the intake manifold). Check:

• The condition of the two small rubber hoses: Are they properly connected, intact, and unobstructed? You can gently blow through them to check if they are not clogged.
• The electrical connector: Is it properly plugged in and clean? Disconnect it and check for the absence of corrosion or bent pins.
• The wires: Visually inspect the harness for any potential damage.

2. Cleaning the EGR Passages and Valve

If the hoses are clogged, replace them. If the EGR valve is accessible, remove it and thoroughly clean the orifice and the valve with a dedicated product to remove carbon deposits. This is an inexpensive operation that often solves the problem.

3. Testing and Replacing the DPFE Sensor

If the previous inspections yielded nothing, the sensor is most likely the cause. Precise testing requires a multimeter to check the reference and signal voltages (consult the repair manual for the specific values for your Mercury model). Often, replacing the DPFE sensor with a quality part is the most direct and effective solution for the P1405 Mercury code.

Conclusion

The P1405 Mercury code is a serious fault that should not be ignored, but it is often simple and inexpensive to repair for a knowledgeable DIYer. By starting with a thorough inspection of the hoses and connections, then proceeding to clean the EGR valve, you have a high chance of resolving the issue. If the fault persists, replacing the DPFE sensor will likely be the final solution to restore your vehicle’s optimal performance and turn off that notorious check engine light.