2010 f350 p0401
 

Hello. So I work for a fleet shop in Vegas and I mostly work on ford trucks. Here is a problem I ran into which inspired me to get into this forum. A little history on this particular vehicle. It came in for a MIL, pulled codes with IDS and I had a code for Exhaust pressure sensor out of range and a P0401 Egr flow insufficient. So I went into service info and found a TSB for PCM flash which contained calibration codes. No problem did the flash to rule out any problems there. Performed driving cycles to set the monitors and both codes came back as I was expecting. Attacked the EP sensor code first since it can actually affect performance of EGR. EP sensor was in fact out of range. Replaced sensor and did not clear codes but ran driving cycles instead to set monitors that way. Everything went alright and both codes got taken care of. Now here comes the tricky part, the vehicle came back with P0401 alone. Started diag immediately and followed pinpoint test, visual inspection for aftermarket items which we don't have since it is a fleet. No obvious wear, damage, or blockage in the intake duct. Checked EGR Volt pid on IDS while whiggling wires without any change, volts within spec. Moved forward to next test. Disconnected EGR valve connector and probed for signal, all good, then tested for shorts to ground, all good. Then tested for short to voltage (koeo)on the terminals for ctrl low and high, and found voltage fluctuating between 4.5 and 5.3 volts on high and .8 to 1 volt on low . According to pinpoint test there should be no voltage in these terminals. With the help of my lead tech we went over the whole test again up to the last point. We disconnected the pcm e connector to check ohms on those terminals. Mind you the wires from the EGR connector to pcm are very short since Pcm is so close to it. Ctrl wires are individual and go straight to pcm. The signal wires are shared amongst map,maf,EP, and crank sensors. We started to disconnect sensors to see if a signal return was back feeding it, no change. Disconnected pcm again and it went away. So we know the short is in that loop. Ohmed wires and all checked out indicating wire integrity. So we came to the conclusion that the pcm is shorted inside providing that unwanted voltage. Am I missing something? I know it is unlikely that a pcm that young would cause that problem. I haven't ruled out a clogged cooler yet but that is because I couldn't even get there due to this finding and can't move forward until I get that short fixed. If anyone has info on this or has replaced a PCM related to this code it would be much appreciated if you let me know.