Ford Repair Questions? Ask a Mechanic for Answers ASAP
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The code P0156 indacates an issues with bank 1 sensor 2 or the connection to it.
Monitor bank 1 sensor 2 on a scan tool to see if there is any reading from it. If there is, the problem is not occurring at this time. Check for shorts or opens of the Red/Light Green (R/LG) wire from sensor #12 to pin 35 of the Powertrain Control Module (PCM) and the Orange (O) wire from the sensor to pin 91. Also check the Purple/Light Green (P/LG) wire from sensor #22 to pin 61 of the PCM for shorts or opens. If the wiring harness checks out OK, replace the sensors.
The code P0401 in most case is a bad DPFE.
Start with checking the Differential Pressure Feedback EGR (DPFE) sensor voltage. This can be done on the scanner or at the DPFE sensor on the Brown/Light Green (BR/LG) wire. The voltage should be close to 1.0v Key On Engine Off (KOEO). If the voltage is incorrect, verify that the Gray/Red (GR/RD) wire is a good ground and that the Brown/White (BR/WH) wire shows 5v. Also be sure the wires are good through the connector and that the connections are good between the pins in the harness connector and the pins of the DPFE sensor. If the Key On Engine Off (KOEO) voltage is incorrect, but everything else looks OK, replace the DPFE sensor and retest. If the voltage is OK, apply 8" vacuum to the "REF" port of the sensor (the smaller of the two ports) and the voltage should increase to at least 4v. If it does not, replace the sensor.