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1999 Ford Expedition OBD2 Error Code P1401: Diagnosis and Fix Guide

Model: 1999 Expedition Fault Code: P1401 Posted: 2005-11-16 22:44

I own a 1999 Ford Expedition with 4WD, 5.4L V8 engine, automatic transmission. The check engine light is on and reactivates shortly after I reset it. The OBD2 diagnostic tool shows error code P1401. What does this code mean exactly? And what steps should I take to resolve the issue? I've already replaced the EGR valve — could that have been a misdiagnosis or is there another root cause? Any expert advice would be greatly appreciated.

Related fault codes

P1401

Comments (3)

Anonymous 2005-11-21 13:58

I recently worked on a 1999 Ford Expedition 4x4 with a 5.4L engine and code P1401. The issue was found to be a broken vacuum hose connected to the EGR valve, located underneath the battery tray on the rear side of the vehicle. Replacing this hose resolved the problem.

Anonymous 2006-01-01 17:36

My daughter's 2001 Ford Ranger (4-cylinder) failed Maryland emissions testing. The check engine light came on about a week prior, and the emissions tester returned code P1401 — 'differential pressure feedback electronic sensor circuit high voltage'. I understand this is often related to EGR systems. I found no vacuum at the EGR valve when increasing RPM while parked. I traced the vacuum line from the EGR to the EGR control valve, which has a vacuum line from the intake manifold and a two-connector plug. The plug consistently shows 12–13 volts across its terminals — whether unplugged or connected, at idle or under load. When I disconnected the vacuum line from the EGR and used a spare hose to apply suction manually, the engine stalled immediately, indicating that the EGR valve itself is functional but not receiving proper vacuum. Is there another way to test the EGR control valve? Shouldn't voltage vary with RPM to allow vacuum flow to the EGR? Am I missing something or should I consider an alternative component?

Anonymous 2006-01-04 21:40

Error code P1401 indicates that the Powertrain Control Module (PCM) does not detect EGR flow. In nearly all cases, this is caused by a faulty DPFE sensor — the Dual Pressure Feedback EGR Sensor. This sensor uses two small silicone hoses to monitor exhaust pressure at different points to determine how much exhaust gas flows into the intake stream. It has one electrical connector. If the EGR valve is internally damaged or inoperative, or if the EGR port is clogged with carbon deposits, no flow will occur. To test: apply vacuum directly to the EGR valve at idle — if the engine stalls or dies, it confirms the EGR is working but not receiving vacuum, pointing strongly toward a faulty DPFE sensor as the root cause.