Chad_Kelsoe Posted December 1, 2017 Share Posted December 1, 2017 So toady I have an 03 F-250 7.3 4R100 trans with the complaint of O/D light flashing and harsh shifting. So I did a KOEO test, retrieved DTC P1747. I notice WSM tells me this is a short circuit in the EPC circuit. So I attempt to perform test E. I only have an IDS, so I can't perform the output test mode. I can't perform any bidirectional controls with the IDS either, so I look over the wiring diagram and try to diagnosis best I can. I have 12 volts to the trans at pin 12, and it lights a test light nice and bright. I don't have the trans tester either to prove out the EPC solenoid, so I check solenoid resistance; 4.3 ohms. Within the pinpoint test range of 3-5 ohms. The control circuit(925 WH/YE) is not shorted to ground anywhere, so at this point I am sure the wiring is ok. The one thing I noticed is at KOEO, measuring across pins 12 and 11 found 12 volts. If I crank the truck, it drops down to .9 volts. Turn the key off, voltage goes away like it should. I should note that on KOEO, I can disconnect the pcm and my ground goes away. I can leave the trans connector unhooked and perform a KOEO on-demand test, and P1747 will continue to set on-demand, along with shift solenoid, trans temp, and TCC solenoid circuit codes( which were expected). At this point, I'm leaning toward the PCM being shorted to ground internally. I did happen to notice the cover for the PCM has been cut like it had a chip installed at one time, but it currently does not have a chip and the plastic plug was installed. But another thing that concerns me is I have trans fluid in the trans connecter. I have noticed this before on other 4R100's, but haven't seen a issue from it. I did drive the truck, I have all the gears but I do have harsh shifts and forward/reverse engagement. Trans fluid is nice and red, not burnt. And trans looks to have been overhauled sometime previously. Any thing else I can test before I quote a PCM? Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted December 2, 2017 Share Posted December 2, 2017 I think the PCM is looking for voltage drop across the EPC solenoid. So disconnecting the harness may not be a valid test. I would load test pin 12. According to the wiring diagram that circuit should have full B+ in start & run. Also the WSM say when the P1747 sets line pressure should be at min pressure, it sounds like yours trans is at max line pressure. If the voltage on pin 81 goes to 8 volts or above KOER when PCM should be commanding EPC (above 70 degrees) & powers & grounds to PCM load test good, I would say that there is cause to believe the PCM is You got a amp clamp for IDS or a DSO? OBD II info for that code says : Current feedback circuit is less then commanded for 5 sec. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted December 2, 2017 Share Posted December 2, 2017 I agree. The thing to remember is that this is a fairly simple code to diag as it is realistically two circuits, a component and the PCM. If the circuits test good and I think load testing is best (Grampy Jim would agree) the WSM should flag the PCM. Not just load test but do a wiggle test while load testing as well AND while testing the circuits for shorts. Circuit 391 feeds ALL of the solenoids however the EPC is isolated by splice S138. Also to add to 8WA's comment, even if the line pressure is at minimum the PCM is in FMEM and all shifting will still be abrupt as all shift strategies go out the window... and the PCM may still be tying and be able to command line pressure high even with the current fault. While PCM failures are not common overall I have had 3 or 4 over the years go bad with trans solenoid circuit concerns. You can't do output state control? Are the PIDS you need to control marked with an ! where the # should be? When that happens the PCM or the scan tool is preventing you from controlling outputs due to the fault or the conditions not being correct to perform the function. Quote Link to comment Share on other sites More sharing options...
Chad_Kelsoe Posted December 4, 2017 Author Share Posted December 4, 2017 I have load tested at pin 12, good voltage and lights a bulb nice and bright in run and start. I need to double check the control circuit, I've been looking at this truck in my free time and can't remember if I load tested the control circuit. I don't have an amp clamp, but my manager said we just got a VCMM so it might be a good time to play with it. I'll have to hook the IDS back up, but in trans data logger none of my pids had the # sign to indicate that I could do any output state controls. I'll try to get the truck back in at lunch and give you guys an update. Quote Link to comment Share on other sites More sharing options...
Chad_Kelsoe Posted December 4, 2017 Author Share Posted December 4, 2017 Ok so I have load tested both circuits while wiggling the harness. Both circuits test good. With the fact that the EPC solenoid resistance is in spec and the wiring is ok, looks like I'm gonna call a PCM on this one. I've seen several PCM failures on 7.3's before( usually due to chips), and never one for this. And I did a screen print on the IDS, none of my pid's have the # sign indicating the ability to control that pid. I've seen the ! come up several times on other trucks, but this truck doesn't even give me the option. And I don't remember too many 7.3 computer's that gave me output control either. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted December 4, 2017 Share Posted December 4, 2017 It is a 4R100 - you could always connect the transmission tester on it if you have one and perform a click test if you were determined to do so. The tester will also let you make resistance checks and even road test and manually shift the truck and engage the torque converter clutch. Rotunda Transmission Tester 007-00085 - Black box has different cables and overlays. Quote Link to comment Share on other sites More sharing options...
8WA Sman Posted December 4, 2017 Share Posted December 4, 2017 Did you happen to check the PCM for any available updates? Quote Link to comment Share on other sites More sharing options...
Chad_Kelsoe Posted December 4, 2017 Author Share Posted December 4, 2017 1 hour ago, Keith Browning said: It is a 4R100 - you could always connect the transmission tester on it if you have one and perform a click test if you were determined to do so. The tester will also let you make resistance checks and even road test and manually shift the truck and engage the torque converter clutch. Rotunda Transmission Tester 007-00085 - Black box has different cables and overlays. I'm pretty sure we don't have the trans tester, but I'll find out. Only been here a 2 weeks now and my shop is separate from the rest, so I'm still learning everyone and what all special tools we still have. Quote Link to comment Share on other sites More sharing options...
Keith Browning Posted December 4, 2017 Share Posted December 4, 2017 You could also install the break out box and ground the control circuit and listen for a click. Sometimes they are difficult to hear especially if the shop is noisy. Quote Link to comment Share on other sites More sharing options...
cbriggs Posted January 3, 2018 Share Posted January 3, 2018 I've had this exact truck with an epc driver internally shorted in the pcm. Had several transmissions changed elsewhere for a very harsh shift, and a trans harness replaced. Eventually it got to me and a pcm fixed it. Quote Link to comment Share on other sites More sharing options...
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