P1405 – DPF EGR Sensor Circuit High Voltage Detected (FORD, LINCOLN, MERCURY)

By Reinier (Contact Me)
Last Updated 2019-09-19
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1405

Table of Contents

1. What Does Code P1405 Mean?
2. Where is the P1405 sensor located?
3. What are the common causes of code P1405?
4. What are the symptoms of code P1405?
5. Get Help with P1405

What Does Code P1405 Mean?

OBD II fault code P1405 is a manufacturer specific code that is (according to some resources) defined by car maker Ford as “DPF EGR Sensor Circuit High Voltage Detected”, and is set when the PCM (Powertrain Control Module) detects a negative exhaust flow while the engine is running with the EGR (Exhaust Gas Recirculation) valve in the closed position. Note that the EGR valve must not merely be in the closed position; it must be commanded closed by the PCM, which state must be verified by the EGR valve’s position sensor.

SPECIAL NOTES: It should be noted that some official Ford sources define code P1405 as “Differential Pressure Feedback Electronic Sensor circuit Upstream Hose”, while others define code P1405 as “DPFE Sensor Upstream Hose Off or Plugged”. Note also that even though the definition“DPF EGR Sensor Circuit High Voltage Detected” does not appear in any official Ford sources, negative exhaust flows (exhaust gas that flows in the wrong direction) can in some cases cause the DPFE (Differential Pressure Feedback Electronic) sensor to register a higher than expected signal voltage, hence the code definition, “DPF EGR Sensor Circuit High Voltage Detected” that appears in some unofficial sources. END OF SPECIAL NOTES.

Unlike most other applications that use dedicated exhaust gas pressure sensors to calculate an efficiency value for the DPF (Diesel Particulate Filter) Ford uses a DPFE (Differential Pressure Feedback Electronic) sensor to measure a pressure differential across the DPF.

In practice, the sensor is not located directly on the exhaust system; it is usually mounted on the firewall, and it connects to the exhaust system with two feed lines that enter the sensor on either side of a pressure-sensing element. In term of it operating principles, the high-pressure side is fitted with a small orifice that allows a small amount of exhaust gas into the sensor. In a fully functional system, the DPFE sensor measures the pressure difference between the high and low sides of the system, and based on the actual pressure difference, the PCM will calculate by how much to open the EGR valve to reduce exhaust emissions.

In practice, the function of the DPF is to trap and hold onto solid particles in the diesel exhaust stream, but being a filter, it starts to clog up after some use, which impedes the free flow of exhaust gas though the exhaust system. However, since the PCM cannot measure or monitor the condition of the DPF directly, it uses the DPFE sensor to measure the pressure of the exhaust gas upstream and downstream of the DPF in order calculate the extent to which the DPF is loaded with soot. When the PCM calculates an efficiency value of about 75%, it will initiate a process to burn off the accumulated soot, which regenerates the DPF and restores its efficiency.

Note though that while several kinds of electrical issues can cause the DPFE sensor to generate a high signal voltage that is indicative of a clogged DPF, other issues such clogged, ruptured, or dislodged exhaust gas feed lines can cause the exhaust gas to flow across the DPFE sensor in a reverse direction, which can also cause a high signal voltage. In practice though, Ford PCM’s are able to distinguish between electrical issues and others such as clogged feed lines, so when a high DPFE signal voltage is detected in the absence of electrical issues, the PCM will set code P1405, and illuminate a warning light.

Where is the P1405 sensor located?

The image above shows a simplified schematic representation of a typical DPFE sensor-based exhaust pressure monitoring system. The two lines indicated by arrows are the exhaust feed lines that can cause code P1405 to set when they rupture, break, leak, or become clogged to the point where exhaust gas can no longer flow through them.

As mentioned elsewhere, the DPFE sensor is typically located on the driver side of the firewall in the engine compartment. To locate the sensor, look for two small-diameter rubber hoses that connect to a single sensor, which is typically made of aluminum.

What are the common causes of code P1405?

Note that while this code does not concern the EGR valve directly, the PCM does use information on the position of the EGR valve’s pintle as a code setting parameter. Thus, in order for this code to set, the EGR valve must be closed (while the engine is running) to ensure that the DPFE measures only the pressure differential across the DPF without the pressure reading being influenced by the presence of recycled exhaust gas. Nonetheless, common causes of code P1405 could include the following-

• Damaged or defective DPFE sensor
• Ruptured, dislodged, clogged, or leaking exhaust gas feed line(s)
• Failed or failing PCM, but note that since this is a rare event, the fault must be sought elsewhere before any control module is replaced

What are the symptoms of code P1405?

Common symptoms of code P1405 could include one or more of the following-

• Stored trouble code and illuminated warning light
• In some cases, multiple additional codes may be present along with P1405
• Fuel consumption may increase
• Varying degrees of power loss may be present
• Idling may be rough or erratic
• Strong odor of exhaust gas may or may not be present
• Vehicle may fail compulsory emissions tests
• In rare cases, the PCM may enforce a no-start condition as a means to protect the DPF

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