2011 FORD F450 DEAD 5V REF MULTIPLE PCMS FIXED!!

Hello everyone, I have a truck that I replaced the PCM due to the injectors cycling while the truck was off. Also had shorted crank sensor wiring that I fixed. Truck ran well made it about 40 miles before a 5v ref circuit for camshaft position, map, egr, and exhaust pressure went to .7 volts. Traced back to the computer again as I could never make the 5v ref come back to life. Even de pinned the harness at PCM to prove it was in the PCM, load tested all main power and ground circuits to PCM. Since they only have reman PCM we got another one. 5v ref immediately came back online and truck drove well again for 40 miles now the same ref circuit is at .7 volts.

Things to note. There is multiple ref circuits coming out of this PCM. Only two circuits coming out of computer have the problem, 1 feeds map, egr and exhaust pressure, the other just feeds the camshaft position sensor. I believe that those two circuits are internally connected inside the PCM. I have removed all sensors, checked for shorts to ground, shorts to other circuits, de pinned both bad circuits at PCM connector. Nothing I do will make this 5 volt ref come back up but I feel confident if I put a new PCM in again it will come back up.

So what could cause the internal 5v regulator to short so bad it wont come back to life. I know you can short these 5 volt refs to ground and they pop right back up when the short is removed so am I looking for Intermittent main power or ground spikes/dropouts that burns that regulator up? I wouldn't think a bad sensor could burn the regulator up.

Please help, I am stumped at this point and could use some direction.

Maybe try scoping the 5 volt reference and see if you’re getting a large spike and taking out the regulator.

I will try that tomorrow morning thank you. what would that tell you? If the ref is shorted to power wouldn’t it stay high? What else makes the internal 5v regulator go bad? Over current?

Mainly checking for interference from another circuit. Like an injector or something spiking the regulator.

I think you're on the right track with your suspicions of a short to power. That's the only thing I could see that'd nuke a 5V reference regulator. Though, I suppose you could short one of the other 5V circuits to ground intentionally, just to see what happens. :silly: If it comes back to life, short to ground is not a suspect. If it doesn't, leave short to ground on the table. Hey, it's getting another PCM anyway, right?

Just curious, what's approximately 40 miles from you? Their home office? Work site? Mostly wondering about some accessory that's been added to this truck that would only get used once the truck gets put to work. If that accessory has a copper short to this 5V reference circuit...

Thanks for the replies yall. I did scope ref this morning, never spiked or came back to life still stuck at .7 volts. I got another pcm in today have not installed yet, its reman, you cant buy a new one.

What I have done is cut the 2 5 volt ref legs that were bad and tied into another 5v leg that is good. So my plan is to drive this thing as much as i can and if the known good leg burns up, I will know its something external causing it. After all Ive only added the load of a cam and map sensor to the good ref circuit so it should not overload it. If it never burns up maybe I will have to chalk it up to multiple bad PCMs, seems unlikely.

Also I did short the known good 5v ref to ground, first with a test light, It actually carried enough current to light my non led test light. Then I pulled the ref circuit all the way to ground with a jumper harness, as soon as I removed the harness my 5v ref came right back online so I feel confident short to ground didn't do this, plus I could never replicate a short to ground/power while checking/ohming/load testing the bad ref circuit.

Another piece of the puzzle. after getting 5v ref good still have a CAM FAULT PID and CAM/CRANK SYNC NO PID on scan tool with extended start, NO CODE. I do have RPM signal. I scoped cam signal input to PCM as the Cam sensor is not able to be accessed easily and I have a great 0-5v clean square wave going into PCM, so why is it not seeing it. Did something burn that part of the circuit up internal to the PCM

I will keep updated with what I do or find.

Update here, just put in new pcm, both of the same 5v ref circuits are still down, sitting at .9 volts. I have already cut both wiring coming out of the pcm and supplied an external 5v to those circuits so I know for sure something is bringing it down at pcm. Ive load tested and scoped all powers and grounds going into the pcm already but I guess I need to go back and do it again because what else is there at this point?

WTF.

Getting on the same page, when you're talking about the two 5V reference legs coming out of the PCM, you're talking about pin #30 and pin #52 of PCM connector C1232E, correct?

Not that I doubted you, but I wanted to make certain that the CMP, MAP, EGR and EBP VREF circuits were actually tied together internal to the PCM, and they are (according to the P06A7 info, anyway):



With #30 and #52 cut at the PCM and after cycling the key, both of those pins remain at .9V?

Ive load tested and scoped all powers and grounds going into the pcm already but I guess I need to go back and do it again because what else is there at this point?

Something in C1232E itself? Green crusties, coolant, water, something like that? I'm sure you've looked at that connector a thousand times by now, just throwing ideas out there.

Yes pin 30 and 52 cut about 3 inches away from connector. I believe they share something internal. Pcm was originally placed due to injectors cycling constantly when vehicle was off. Also found some weird substance inside the connector at that time, cleaned out/replaced pcm and fixed that issue. I depinned circuit 30 once to inspect the terminal closely.

I have also unplugged c1232e and cycled key, 5v ref never came back.

Only thing I know to do is go back to main powers and grounds…lost lol

Wfliles wrote:

Only thing I know to do is go back to main powers and grounds…lost lol

I've been going over all the engine controls diagrams, looking at the various VREF circuits. Trying to find SOMETHING.

I ran across the Reductant Pressure Sensor, shown here:



It's got a VREF circuit, but for some reason doesn't show up on the list of sensors associated with each 5V reference circuit I found earlier:



The RDP does eventually show up in the 'B: Reference Voltage (VREF)' testing chart, but it's WAY down there at B18.

Anyway, that's my theory - There's another 5V reference circuit out there that's shorted. It's not on pin 30 and 52 of C1232E, but it's tied into this regulator somehow. And the service info may not be completely accurate.

I'd be very interested to see if what happens if you cut pin 1 grey/yellow at C1232T and cycle the key. If the other two 5V reference circuits come back to life, then your problem lies somewhere in the RDP circuit. If nothing changes, you can curse my name while you fix the wire. :lol:

YOU GOT IT!!!

It was the 5v ref for the reductant pressure sensor bringing it down. I knew I had it as soon as I tested voltage at that pin 1 and saw it at .9 volts as well. Cut the wire and 5v ref came right back up. Ref wire had about 20 ohms of resistance on it to ground and it lost ground when I unplugged the connector on top of the DEF tank. Not going to diag further as this vehicle doesn't utilize DEF anymore.

I remember seeing that sensor come up while researching, but so did crank and other sensors that did not have issues. Also that circuit number is different so i just did not dig in more and should have.

My first thought was man I need to offer this guy a job lol. Cant thank you enough its awesome to come onto the forum and speak the same language as others when it comes to electrical diagnosis as its rare to find folks who have a good understanding. If you're ever in the Fuquay-Varina, NC area let me know Id love to get you lunch or something for the help.

Nice! :woohoo:

Give yourself a pat on the back (or a few beers) for staying with it. That was NOT a straightforward diagnosis. Lot of shops would have shipped it to the dealer long ago. And there's no guarantee that they would have done any better. :lol:

I remember seeing that sensor come up while researching, but so did crank and other sensors that did not have issues. Also that circuit number is different so i just did not dig in more and should have.

Service info could definitely be clearer about which sensors use which regulators.

If you're ever in the Fuquay-Varina, NC area let me know Id love to get you lunch or something for the help.

I've never been to NC, but I'll take you up on your lunch offer if I'm ever in the area.