Code P0761, log data inside. Help, advice needed

[96ExplorerSport]

Hi guys,

Need your help. I have 96 X with 4R55E transmission. I've had this CEL light for a while. I've tried erasing it in the past, but it usually comes back after 3-4 weeks of driving. Now it comes back each week, so it's easier to reproduce. I am now at the point where I know how to trigger CEL while driving with a logger. I recently acquired OBD-2 scan tool that allows me to data log all engine/transmission sensors. That's what I did, so here is what is going on.

First of all, P0761 refers to SSC, which I replaced already and it did not fix the problem. I also checked my throttle sensor output (TP). Logger reports 0.96V (19%) at idle and 4.6v (93%) at WOT.

Here are the conditions leading to CEL. From a stop, I apply 30% throttle (idle was 20%, so 30% is a light throttle). Truck starts accelerating and goes through 1, 2, and 3 gears. I can see PCM commanding gears 1,2,3, and corresponding solenoids (A,B,C) switching and RPMs dropping accordingly. I am now in third gear going around 60MPH and accelerating (still 30% throttle). RPMs are around 2200. At that point I can see PCM requesting 4th gear, SSC solenoid gets "ON" signal but nothing happens. Truck keeps accelerating in 3rd gear with RPMs going up. I can make it go like that for a while as long as I stay on the throttle (30%). The moment I lift the throttle ( < 24%) the transmission shifts into 4th gear and RPMs drop. If I do not lift the throttle, transmission does not shift, and after 20 seconds or so O/D light starts flashing leading to CEL later on. Obviously it detects that RPMs and VSS do not match with gear requested and it thinks it's SSC fault.

So the problem is that the transmission does not **** into 4th gear under the above conditions. It always shift when I step of the gas. SSC solenoid is brand new. What else should I check? It's interesting that I can make it shift by lifting the throttle. What is the relation between TP and shifting? Manual mentions that transmission won't switch in O/D if there is a problem with EPC solenoid. Is this a possibility here based on my symptoms? Is there a way to check EPC operation versus TP?

This weekend I am going to adjust O/D band, just in case. What else can it be? I can provide for data if you tell me which parameters to log.

Looking for an advice,
Sergey

 

[Glacier991]

P0761 is one of those codes that reflects a purely electrical issue. Whereas some codes can show up for either mechanical or electrical reasons (or hydraulic), this code is ONLY generated by an electrical fault.

Ok, that said... you have already replaced the solenoid. The next thing to check is the internal harness for shorts and then the main wiring harness. FORD's test procedures for this are pinpoint test A, which involves using a breakout box, the transmission tester and even an NGS tester.

While I suppose a bad input to the PCM could be responsible, I'm guessing it is in the wiring somewhere. Or at least would want to exhaust all wiring possibilities before moving on.

While I hate to throw parts at any problem, ever, if you wanted to try the brute force approach, I'd replace the internal wiring harness first.

 

[96ExplorerSport]

Thanks for replying Glacier991. Internal harness has been replaced already and I also checked it last time I dropped the pan. I could not find anything wrong with it. I'll check the manual for the pinpoint test A.

The thing that bugs me is that transmission switches fine when I ease on gas. Can you you explain me what happens when PCM requests gear 4 and switches SSC ON? Assuming that SSC is ON, how does the actual shift occur? Where does TP signal come in? Does the pressure inside the valve body change depending on TP signal? The manual does say that O/D and 2nd gear wont work properly if EPC solenoid does not operate properly. Is there an easy (w/o NGS) way to test it?

Thanks,
Sergey

 

[Macgiobuin]

Same code, same car I experienced. '96 Exp Sport; P0761; no OD. I replaced the SS3, with no change. But I licked it. The code shows up when, after activating SS3, the PCM does not detect the reduction in RPM's associated with proper function. So, a mechanical cause can be the culprit. How to fix? Move the heat shield away from the OD servo port. Take the circle clip out of the servo port hole. This can be hard because the catalytic/exhaust is in the way, you only have about 1.5 inches to work with. Spray liberally with WD40 or gumout. The servo cover will probably be gunked in there because the cause of the problem is heat. Take the OD band adjusting nut and adjuster out. Take the nut off the adjuster. Put the adjuster back in and tighten it until the servo cover pops out enough for you to grab and twist it out. Take out the servo piston and spring. Eureka! The piston's rubber lips are hard as granite and razor sharp, causing the piston to stick in the servo cylinder most or all the time. So: either replace the piston, or, do what I did: take a 200 grit sandpaper and smooth the sharp edges all around, only about .2 mm, enough to make it dull (not sharp) on both bearing edges. Check the bore surfaces for crud, cleaning them with fine steel wool if necessary. Put it back together but first take out the band adjuster. Reinstall the spring and piston and cover and clip. Install the adjuster all the way, then back it off 1.25 turns. Install the jam nut. Reset the shield. You just saved a $1200 rebuild.

 

[Red_Lion]

Same code, same car I experienced. '96 Exp Sport; P0761; no OD. I replaced the SS3, with no change. But I licked it. The code shows up when, after activating SS3, the PCM does not detect the reduction in RPM's associated with proper function. So, a mechanical cause can be the culprit. How to fix? Move the heat shield away from the OD servo port. Take the circle clip out of the servo port hole. This can be hard because the catalytic/exhaust is in the way, you only have about 1.5 inches to work with. Spray liberally with WD40 or gumout. The servo cover will probably be gunked in there because the cause of the problem is heat. Take the OD band adjusting nut and adjuster out. Take the nut off the adjuster. Put the adjuster back in and tighten it until the servo cover pops out enough for you to grab and twist it out. Take out the servo piston and spring. Eureka! The piston's rubber lips are hard as granite and razor sharp, causing the piston to stick in the servo cylinder most or all the time. So: either replace the piston, or, do what I did: take a 200 grit sandpaper and smooth the sharp edges all around, only about .2 mm, enough to make it dull (not sharp) on both bearing edges. Check the bore surfaces for crud, cleaning them with fine steel wool if necessary. Put it back together but first take out the band adjuster. Reinstall the spring and piston and cover and clip. Install the adjuster all the way, then back it off 1.25 turns. Install the jam nut. Reset the shield. You just saved a $1200 rebuild.

Hi Macgiobuin, I am having the same issue. Could you break this down a little for me or is there is a visual tear down of this? I would love to see if this fixes my issue. I know this is an old thread, but would love to try this.

 

[Macgiobuin]

x unable to post pictures