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The common reason for the code P0401 in most case is set due to a bad DPFE sensor. If you have replaced it and are still setting the code I would suspect you have restricted EGR passages in the throttle body. Run this test,
Check Key On, Engine Off (KOEO) voltage of the Differential Pressure Feedback EGR (DPFE) sensor. Voltage should be 0.5-01.2 volts.If static voltage of the sensor is incorrect, check the circuits of the DPFE sensor before replacing it. The Brown/White (BR/WT) wire is a 5-volt reference signal. The Grey/Red (GY/RD) wire is sensor ground. The Brown/Light Green (BR/LG) wire is the sensor signal circuit.With the engine idling, open the Exhaust Gas Recirculation (EGR) valve with a hand-held vacuum pump. The engine should act like it is misfiring on several cylinders and the DPFE sensor voltage should increase to greater than 4.0 volts.If the engine RPM decreases severely, but the sensor voltage does not react properly, replace the DPFE sensor. Slowly open and close the EGR valve with a hand-held vacuum pump to verify that the valve does not "stick" in its bore. If the engine RPM does not drop severely when the EGR valve is opened at idle, remove the throttle body and gasket and clean the EGR flow passages of carbon.
I've got how to get the throttle body off, but how does the EGR tube come off? I can figure out how to get it disconnected from the back of the engine.
Also, when checking the voltages on the DPFE sensor, am I checking those with the connector on it? And what wire am I looking for that 0.5-1.2 volts on?
The brown wire is the 5 volt reference signel with the connector pluged in. There shouldnt be any reason to remove the EGR tube to clean the passages. If your removing it you will have to loosen the nut on the back side, see the picture I sent.