Code P1401-Differential Pressure Feedback Electronic (DPFE) sensor signal was over 4.0 volts.
Enabling conditions: Engine off self test.
Blocking Action: This code can block the following monitors: Fuel control, O2 monitor, catalyst, misfire, and EGR monitor.
Testing: Check for an open ground for the sensor, damaged sensor or a short to 5 volt reference in the signal wiring.
Engine Off:
The EGR can’t have flow with the engine off, The engine off voltage is the base line for engine idle testing. The normal voltage is 0.45 to 0.60 V sensor range. The new plastic low profile sensor is the 0.9 to 1.1 V version with some of the older versions being the new 0.9 to 1.1 V version too. If the signal voltage is wrong check the 5 V reference and ground before replacing the sensor.
5 Volt Reference Check;
Note: 5 V reference is shared with other sensors.
The sensor requires 5 Volt reference to operate properly. Check for 4.9 to 5.1 V using battery – as reference. If voltage reading is too high, check the grounds because they are the most likely cause of a high reference voltage
reading. Low 5 V reference is usually caused by a short to ground.
Sensor Ground Check;
Check for 0.050 volts between sensor ground at the sensor and battery negative. Note: Sensor ground is shared with other sensors.
Normal ground voltage and reference voltage with wrong signal voltage indicates the sensor is bad.
If the voltage is too high check the voltage on the PCM ground to battery negative.
– High voltage indicates the PCM to engine ground or battery to engine ground is bad.
– Normal PCM ground voltage with high sensor ground indicates a prob-
lem at the PCM connector or inside the PCM.