My 6.5L TD has been giving codes 17, 18, 34, 35. So I replaced the Optical encoder in the IP, the Encoder harness filter, the FSD(PMD), I also made sure there are no leaks/air leaks in the fuel supply and return. No change, intermittemt stall and SES light on in limp mode. I got a code 54 a few weeks ago. Then the Front axle (it's a 4WD) actuator quit engaging the front axle. I checked codes and now I get 18, 35, 54, 84, 99. I notice the new ones- 84 and 99- have something to do with a 5 volt reference voltage for the throttle (gas pedal) position sensor. I believe the 54 code is also tied to a 5 volt supply. The wiring diagram shows the front axle/4WD circuit going into and out of the EMC. Do I have a bad EMC quad driver? Is the front axle actuator power controlled by the ECM- the same driver as the IP? I'm about ready to order a refurbished ECM and want to know if that's the right move.
I'm not the best on diesels but am sending you rtwo diagnostic charts for code 18 and 35 the other three kind of lead to a bad pcm. But also check your battery as if it is bad it will sendout false codes. As far as the 4wd circuit check your fuses and usually if a quad driver is bad it's time for a pcm. The power for actuator is controlled by switch on dash with a relay underhood. I hate to tell you to order a ecm because it would be better if you had one available to see if it fixes things first. I'm sending a diagram of 4wd circuit. Because you have a diesel the transmission is run by it'won ecm and power is direct for 4wd as you'll see in circuit.I fyou get to code 54 the most that that stuff say sis replace ecm so I hope this helps.