During long drive over the weekend my check engine light came on with one code: 1406 - Differential Pressure Feedback Electronic Sensor Circuit Downstream Hose.
I have a 97 5.4L with 98K mi. It feels like there is a slight decrease in performance, especially at about 40mph in overdrive when engine is turning at about 1500 RPM. Trying to hold that speed, the engine will start to get choppy/jerky.

Can anyone shed any light on what the code means?
Thanks,
John

 

This sensor registers a certain voltage depending on EGR flow. MAke sure you don't have a clog or a vacuum leak in the EGR system. Read the manual for more info.

 

First, thanks for reply SuperDPFE.
Through some research I found that the code refers to a sensor that works in conjunction with the EGR. DPF-EGR or Differential Pressure Feedback Exhaust Gas Recirculation sensor. Does this have anything to do with your login name SuperDPFE?
At first I thought the code scanner description had something to do with the rear differential. .
The DPF-EGR is mounted next to the throttle body and has 2 hoses going to the EGR tube. One is a downstream hose (smaller) and the other is the upstream hose (larger). I removed the hoses and found some dirt but definitly not clogged. I then removed the DPF-EGR and found the downstream inlet completed clogged with a crusty dry material. I used a small drill and worked it in by hand while holding the DPF-EGR so the tub pointed down so no material would fall into the sensor. I cleaned the upstream tube with a little larger drill while I was at it and put it back together. I then cleared the code and we'll see what happens. I'll post back if the check engine light comes back on.
~john

 

Yes - I was once obsessed with trying to find out why the OBDII code I was registering meant low flow through my EGR. I ended up taking my DPFE sensor apart only to put it back together with 6 screws (there was nothing wrong with the EGR valve or the DPFE sensor.) The problem turned out to be a broken vacuum line (skinny green actuator line) going to the EGR valve. I'm glad you think you found your problem. Let me know how you make out. On another note, I just paid Ford $1000 to replace my AC compressor. Don't EVER go to the dealership. It's NEVER worth it. The next day my truck wouldn't start. Yesterday I tracked the starter problem to the fact that the battery line lug had corroded at the starter solenoid and broken off. Got a lug and crimped it back on and I'm back in business. Cost, 25 cents. Take care.

 

What is the best way to search out vaccum leaks on the 5.4? The ol'spary and listen to rpm change doesnt' seem to work well on fuel injected motors if it is anything like my mustang, unless it is a large scale vaccum leak.

Thanks,

Rod

 

The code hadn't come back since I cleaned the DPF-EGR sensor. Runs much better too!
I also considered taking the DPF-EGR apart by drilling out the rivets but since the problem was obvious i figured i'd save that fun for another time.

 

having the same problem code p1406 downstream hose clogged undone on 2003 ford 150 4.6 i replaced both the hoses and the dpfe sensor itself any suggestions? doesnt affect performance at all... Thanks ahead of time

 

Okay here is the checklist from Ford.
The ICE one gets the trucks in the cold area below 32 degrees temp the most.
Make sure to read all of this and go by the steps.

What are the common causes of code P1406?

Common causes Ford code P1406 could include the following-

• Downstream DPFE hose is disconnected, perforated, split, cracked, or dislodged.
• Downstream DPFE hose is plugged, clogged, restricted, iced-up, kinked, pinched, or otherwise prevented from allowing a free flow of exhaust gas
• EGR feed pipe may be blocked, clogged up, or restricted by ice
• Defective DPFE sensor
• While electrical issues in the DPFE sensors’ control circuit can cause code P1406, the actual cause of this code is unlikely to be electrical in nature if there are no control circuit related codes present.
• Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced

What are the symptoms of code P1406?

Apart from a stored trouble code and possibly an illuminated warning light, it is unlikely that any other noticeable symptoms will be present, and especially driveability issues since the EGR valve remain closed.

How do you troubleshoot code P1406?

SPECIAL NOTES: It should be borne in mind that the combustion process creates large quantities of moisture that can cause failures of the EGR system when the moisture freezes in low ambient temperature conditions. To avoid false codes caused by freezing moisture, the following logic is used by most manufacturers-

• If the ambient temperature is below 320F (0oC), and the moisture in the system freezes, causing code P1406 to be set, the EGR system is disabled for the current drive cycle, but the fault is not stored although the EGR monitor continues to run. The EGR system is only re-enabled when the monitor detects that the ambient temperature has risen above 320F (0oC).
• If the ambient temperature is above 320F (0oC) and a fault is detected, both the EGR system and the EGR monitor are disabled, and a code is stored. On applications that use warning lights to indicate issues with the EGR system, this light will (in most cases) be illuminated if the fault persists for three consecutive drive cycles. END OF SPECIAL NOTES.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

Step 2

Refer to the manual to identify and locate the DPFE sensor, its two hoses, and its wiring. Consult the manual to determine which hose is the downstream hose, as well as the function and color-coding of each wire in the DPFE sensor electrical connector for future reference.

Step 3

Once the downstream hose is identified, perform a thorough visual inspection of it, but be sure to inspect the entire length of the hose for splits, cracks, perforations, kinks, bends, and the tightness of all connections where the hose attaches to other pipes, hoses, or the DPFE sensor itself. Replace both hoses as a set if any damage to the downstream hose is found.

NOTE: While it may sometimes not be strictly necessary to replace both hoses, doing so ensures that both hoses are fully serviceable.

Step 4

If no visible damage to the downstream hose is found, remove the hose and attempt to blow through it. Air should flow through the hose with no resistance, but bear in mind that in some cases, the hose could be partially clogged by exhaust deposits.

To check if this is the case, run a piece of steel wire through the hose to check for obstructions, but take care not to poke holes in the soft material of the hose. Replace the hose if there is any doubt about its condition, or its ability to allow a free flow of exhaust gas through it.

Step 5

In some cases, it is possible for the orifice in the EGR feed pipe to become clogged, or even for the EGR feed pipe itself to clog up with carbon or exhaust residues. Thus, if the downstream hose is known to be clear, remove the EGR feed pipe and inspect it for restrictions or blockages. Remove blockages as required, but note that in many cases, simply replacing the pipe with an OEM part is the easiest and quickest way to ensure that the pipe is not restricted.

However, if the EGR feed pipe is not to be replaced, block off one end and one of the DPFE sensor tubes. Blow compressed air through the pipe to see if the orifice is clear, and replace the pipe if there is any doubt about whether the orifice is open enough or not.

Step 6

Reinstall all parts, but make sure that all connections are properly gas-tight. Clear all codes, and operate the vehicle for at least one complete drive cycle to see if the code returns.

Step 7

If the code does return but all hoses and tubes are known to be clear, suspect a defective DPFE sensor. If the scanner has control functions, use it to command the EGR valve open while the engine is idling; if the DPFE sensor is working as intended, the idling quality will deteriorate, and the engine may stall because exhaust gas is being introduced.

If, on the other hand, the engine does not react when the EGR valve is commanded open, it is almost certain that the DPFE sensor is defective, or when an electrical fault in the sensors’ control circuit is the cause of the problem.

NOTE: It is of course possible that the EGR valve is defective if the engine does not react, but this is always indicated by a dedicated or specific EGR valve-related code. If no such codes are present, either active or pending, replacement of the DPFE sensor with an OEM part, or checking for electrical faults in the sensors’ control circuit will almost certainly resolve code P1406.

Step 8

Therefore, if the fault persists, perform reference voltage, resistance, continuity, and ground checks on this circuit as per the instructions provided in the manual. However, electrical faults of this nature are almost always indicated dedicated codes, which means that if no such codes are present, the fault is unlikely to be electrical in nature. Nonetheless, there is no harm in checking that all electrical values conform to specified values, but be sure to disconnect all wiring from the PCM during resistance tests to prevent damage to the controller.

If discrepancies are found, make repairs as required to ensure that all electrical values conform to specifications, clear all codes, and operate the vehicle for at least one complete drive cycle to see if the code returns.

Step 9

In the highly unlikely event that the code does return, suspect a defective DPFE sensor. Refer to the manual for detailed information on the correct procedure to follow to test the DPFE sensor, and replace the sensor if it does not conform to specified values, and particularly with regard to its internal resistance.

NOTE: DPFE sensors are not repairable, which means that replacement of the sensor is the only reliable remedy should testing prove the sensor to be defective.

Step 10

Clear all codes after the sensor replacement, and operate the vehicle for at least one complete drive cycle to see if the code returns. In the highly unlikely event that the code does return, suspect a defective PCM, or programming error. Note though that if this is suspected, it might be necessary to refer the vehicle to the dealer or other competent repair shop for professional diagnosis and repair, since many, if not most generic code readers cannot detect PCM or programming related faults.

Hope this stolen information helps.