Guys,
Need some input on an issue I have been having. Torque converter is unlocking and relocking at speeds above 45 mph or so. It is a BTS trans, No lights on the dash, nothing, still shifts fine. It only does it once the truck is warmed up and it will do it 5-6 times then it goes away. If I shut the truck off and restart it, it does it over again. Typically these are right on the money.


So I hooked up AE and I only got one real code which I think is unrelated.
P1876 - Transfer Case 2-Wheel Drive Solenoid Circuit Failure. 4wd still works.


Then I opened up the ABS module in AE and watched the wheel speed sensors. The rear VSS is reading correct but the front two ABS sensors in the wheel bearings are consistently low. They are pretty close as you start out but once you get going they end up being about 7 mph low compared to the rear VSS. Then I see them spike to like 85 mph when I am going 55-60 mph. Only one side will spike at a time but both sides will spike.


- What I have done so far is swapped out the TPS to another used one I had and that really didn't change anything.

- Unhooked the alternator and drove to make sure it wasn't creating some kind of issue.

- Then I reconnected the batteries and made sure it all is nice and tight!

- I also pulled off the front wheels and brakes and inspected the ABS sensors in the wheel bearings. They looked good. Ohms read about 700 each. I think that was within spec.

- Unplugged the PCM and there was a touch of moisture between the plug and the PCM. Dried that all out stuck some dielectric grease in there and then drove the truck.

- Stuck a new PCM in there to make sure it was ok.

- Pulled the rear speed sensor cleaned it and put some dielectric grease on it. (Have not drove yet after this fix)

- When I inspected the electrical plug on the tranny (passenger side) it was full of oil and I suspected there must be some short in it. Cleaned it off and put some dielectric grease on it. Nothing changed.

- Disconnected the front ABS sensors and drove, nothing changed.

- Pulled the fuse for the ABS module and nothing changed.

- Removed my LED third brake light & installed stock one.

- Inspected and made sure all my brake lights work.


Anybody have thoughts on this issue, it has to be something electrical causing it.

How does the PCM read the speed sensors and run your speedo? It looks like the front ABS sensors run in to the ABS module and then to the PCM. I am just wondering how the front speed sensors can be so far off and spastic as well. Both PCM's read the incorrect abs sensors for the front. Do the front ABS sensors have any impact on how the truck shifts or locks the converter? Typically all three of these sensors are right on the money on my truck.

It is just weird to have the truck warm up and then this issue happens, then it disappears till you start the truck again!

Any help from my FTE friends would be great.

 

I haven't toyed much with ABS, outside tire size. If I had shift issues, my first AE visit would be to the EBP sensor - both KOEO and KOER under load. The TCLU is also controlled by the Engine Oil Temperature... which sounds more suspect than anything else right now. With no signal, the PCM might "think" the truck is cold, then give a fixed time before it assumes the temperature reaches normal... giving normal TCLU. I'd look at EOT volts/temperature.

 

According to what I've been told by a Ford tech....
One of the primary concerns is to keep the engine running whenever possible so almost all PCM calibrations have methods to accomplish this. During a panic stop or forceful application of the brakes...one of the very first things the PCM does is unlock the TC to avoid stalling the engine. Not normally a big concern with these trucks unless it's in 4WD or inclement conditions (mud, snow, ice etc). I don't know enough about the programming to determine if this is true or not.... but if so, then the P1876 may actually be related somehow. Just throwing that out there to chew on...

That almost sounds like a smoking gun to me.....A bad solenoid pack could very wall cause the symptom you describe.

Kinda rules out the ABS system as the issue. Nice idea though!


My understanding is the ABS module compiles the data from the wheel speed sensors and then feeds a MPH value to the PCM via the SCP bus line. If the rear wheel speed sensor fails and the vehicle has front ABS sensors then the ABS module can still determine a MPH value. If the ABS module fails then cruise control should be disabled and the PCM will look at the VSS for MPH value. All these conditions should throw a light of some kind. Either the SES or ABS light....or both.

Since you have AE. Have you monitored the Torque Converter Clutch Modulated PID while the symptom occurs? Depending on the year of your truck...you might also have Torque Converter Slip Actual, which can also be useful. Some of the PID values in AE don't show up for the 1999 models.....the easy work around is to lie to AE and say that you have a 2000 or 2001 model instead and then you'll have everything available.

It would be very helpful to see what the PCM is asking the TC lock up solenoid to do. You can monitor that with AE. That data might give you some ideas what to check.

Hope this helps.

 

I will definitely take a look at that. Thanks.

Yeah I was thinking the same thing that possibly it could be related on the transfer case code. Mainly since I normally don't have this code....


I have watched the torque converter lock and unlock and the slip. You can watch it unlock and lock up. It is very strange. So are you thinking that a bad solenoid pack in the tranny can do this? Due to the short on the electrical plug? This has been a tough one and just trying to figure this out without throwing a bunch of money at it... LOL

Maybe I will give Brian a call on this and see what he thinks.

 

If TC Clutch Modulated is 100% and TC slip is very low (1-5 rpm) that would be a normal condition. If TC Clutch Modulated is 100% and TC slip is 300-600 that would indicate a problem with the wiring, solenoid pack or something else inside the transmission.

If you are observing the TCC Modulated at anything less than 100% then the PCM is commanding the action and your transmission is simply doing what it's told. In that event, you will need to determine why the PCM is calling for the TC to unlock. One thing to look at while having AE out is the Brake Pedal Apply switch. Off should be "0" and On should be "1". Does your cruise control work? Is your speedometer accurate?

Do you happen to have a PTO transmission by any chance? If so, are you using the key on 12v power wire from the PTO Control Circuit for anything inside the cab?

 

All good questions, waiting to here on this one also.

 

Nope no PTO tranny.

Took it for a run tonight. On a cold engine/tranny I was seeing 100% TC lockup and I was seeing a constant 10-15 RPM slippage at 55 mph. Once the truck was warmed up I was seeing constant numbers like 50-60.

At 65-70 I would see numbers significantly higher in the range of 150-200 for slippage.

I was still seeing little spikes of 200+ RPM and I could see the converter unlocking.

Seems like the numbers I am seeing while locked up are higher than normal. I will look at it a little more tomorrow at work, this laptop screen sucks for looking at data. I could post the data as well.

I still am unsure on how the front ABS sensors are affected by this. Is this solenoid easy to replace or does the tranny have to come out...LOL

 

Also, for some reason since I pulled the fuse for the ABS and unplugged and plugged back in the front ABS sensors the codes won't go away? I have no light on in the dash? I clear the three codes and they come back! Any ideas on this?
Thanks for the help.

 

I think you need to call BTS in the morning and explain your symptoms. Mention that you are observing TC slip while the clutch solenoid is commanding 100% duty cycle.

 

Will do, still don't get these front abs readings?

 

Me either. That is an odd issue. Does your ABS light work? It will illuminate briefly when the key is first turned on. If the ABS module detects an error, then the PCM will determine mph some other way.

The thing that has me more baffled is that your OD light should be flashing when the TC is slipping. In fourth gear and TC locked, the OSS should be 71% of engine speed. Or another way to look at it is that TSS should match engine rpm when the TC is locked.

Edit:I said that backwards....the engine speed should be 71% of the OSS....(now I am getting myself confused...)

 

What do you mean by OSS? or TSS?

Went out and checked that the ABS light does come on when I start it.

That is why I wonder about the front wheel speed sensors. The path of how they are read by the PCM. They go to the ABS module, then to the PCM or do they go through the GEM? I just wonder if one of those is messed up enough to tweek and spike the values without setting any kind of codes. I might see if I can throw a friends ABS module in there to test it out. I just don't know how the tranny issue and the wheel speed sensors are related.

 

The ABS determines mph....this is why you need to switch over to the ABS system in order to calibrate the speedometer.

OSS is Output Shaft Speed (tail shaft of transmission). Also is the same as driveshaft speed and pinion gear speed.

TSS is Turbine Shaft Speed or what I sometimes call the input shaft of the transmission. The input shaft is driven by the turbine inside the torque converter.

The outer case of the torque converter is bolted to the flexplate which is bolted to the crankshaft. So, engine rpm is the same as TC case speed. When the TC clutch is applied, then engine rpm is the same as TSS (or very close).

The sensor in the differential is the VSS (vehicle speed sensor) but it really just measures the ring gear speed. If the ABS module knows the ring gear speed and tire diameter, then it can calculate mph.

Right now I would be looking at why TC clutch is 100% yet you are observing several hundred rpms of slip. That sounds like an issue with the TC. Did I understand you correctly in your earlier post? TC clutch modulated is 100% at the same time you are seeing 200-300 rpm of slippage?

 

Yep 100% lockup and 150-200+ slippage at times.

 

How the heck do I upload a pdf on here?