Ford P1406 Code: DPFE Sensor Downstream Hose Off or Plugged
The hose between Ford's DPFE sensor and the EGR-valve side of the orifice is off, leaking or blocked.
At a glance
Severity: Low
- Meaning
- DPFE Sensor Downstream Hose Off or Plugged
- System
- Emission Controls · Powertrain
- Safe to drive?
- Yes, short term
- Typical repair cost
- $0–$400
- DIY difficulty
- Easy
On EEC-V era Fords the DPFE sensor compares pressure on both sides of a restriction in the EGR tube. The downstream hose picks up pressure between that orifice and the EGR valve, which drops sharply the moment the valve opens to intake vacuum. If that hose is off, cracked or blocked, the sensor's reference side sees outside air or a trapped pressure instead, so with the valve shut the signal reads higher than its engine-off baseline, as if exhaust were flowing when it isn't. The PCM spots that implausible reading and stores P1406. Because the PCM then believes EGR is already flowing, it may trim EGR back, which is why pinging and a NOx failure can follow on trucks and vans such as the F-150, E-Series, Ranger and Windstar.
Can I keep driving? You can drive normally in the short term. Keep an ear out for pinging under load, use the recommended octane, and get it fixed before an emissions test or before towing heavy loads.
How to read P1406
- P Powertrain
- 1 Manufacturer-specific
- 4 Auxiliary emission controls
- 06 Specific fault
Symptoms
- Check engine light with P1406, sometimes together with P1405
- Spark knock under load because the PCM thinks EGR is flowing and cuts it back
- Idle a little uneven if the EGR valve itself is also leaking
- DPFE reading above its key-on baseline at idle with EGR commanded off
- Soot-blackened hose end or a hose lying loose next to the EGR valve
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Downstream hose off, cracked or split where it pushes onto the tube nipple next to the EGR valve
- Downstream pickup port on the EGR tube clogged by carbon that builds up right behind the orifice
- Water trapped and frozen in a low loop of the downstream hose
- Hoses swapped between the HI and REF ports
- DPFE sensor diaphragm or port damaged
- EGR valve not seating, so the sensor sees flow at idle
Diagnosis step by step
Compare engine-off and idle readings
Record the DPFE voltage key on, engine off, then at warm idle with EGR commanded off. Idle should be within a few hundredths of a volt of the key-on figure; a clearly higher idle reading fits a downstream hose problem or a valve leaking exhaust.
Tools: OBD-II scanner, Multimeter
Leak-test the downstream hose
Remove the hose, cap one end with your finger and draw vacuum on the other with a hand pump. It must hold steady; if the needle falls, the hose has a crack you may not see, especially at the ends that were stretched over the nipples.
Tools: Vacuum gauge
Clear the downstream tube port
This port sits where soot collects just past the orifice. With the engine cold, open it by hand with a small drill bit or stiff wire, then blow through it; take care not to widen it.
Tools: Flashlight
Check the EGR valve seal
On vacuum-operated valves, look for the diaphragm resting fully down at idle and check the vacuum line to it isn't carrying vacuum at idle. A valve that doesn't seat lets exhaust move through the orifice and can mimic this code; remove it and inspect the seat for carbon.
Tools: Vacuum gauge, Screwdriver
Confirm port orientation and routing
Make sure the REF (downstream) port on the sensor goes to the nipple beside the EGR valve and that the hose runs uphill to the sensor with no sag where water can collect.
Tools: Flashlight
Clear the code and re-run the monitor
After the repair, clear codes and drive at steady cruise with gentle acceleration. The EGR monitor must complete before the vehicle is ready for an emissions test.
Tools: OBD-II scanner
Where the parts are
- 1MAF sensor
- 2Turbocharger
- 3Throttle body
- 4Intake manifold
- 5Fuel injector
- 6EGR valve
- 7Fuel pump
- 8Thermostat
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Replace downstream DPFE hose (both recommended) | Yes | $15–$90 |
| Clean EGR tube pickup port | Yes | $0–$120 |
| Clean or replace EGR valve | Yes | $60–$350 |
| Replace DPFE sensor | Yes | $90–$260 |
| Replace EGR tube assembly | No | $150–$400 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With P1406 stored the check engine light is on and the vehicle fails an OBD emissions test. Some states also run a tailpipe test on older trucks, where reduced EGR can push NOx over the limit.
Frequently asked questions
Why does my DPFE read as if EGR is flowing when the engine is idling?
Because its reference side is seeing the wrong pressure. With the downstream hose off or cracked, the sensor compares exhaust pressure with outside air instead of the pressure behind the orifice, so it reports flow that isn't there.
Can a leaking EGR valve cause P1406?
It can contribute. A valve that doesn't close lets exhaust move through the orifice at idle, which raises the DPFE signal the same way a disconnected downstream hose does. Check both before buying parts.
Which hose is the downstream one?
It's the hose from the sensor to the nipple closest to the EGR valve, after the orifice in the tube. On many sensors that port is marked REF, while the upstream one is marked HI.
Is P1406 the same as P0401?
No. P0401 means the PCM measured too little EGR flow, while P1406 means one of the measuring hoses is faulty. A bad downstream hose can lead to either code, so fix the hose first and see whether P0401 returns.
Sources
- Manufacturer public service information (cross-checked)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy