8 Speed Shifing Issue

[tyallis]

Vehicle: 2015 1500 4WD outdoorsman Hemi 8 speed. 175,000 miles.

Folks,
I've got a recurring issue that has both myself and the local small-town mechanic stupped. A year ago (and 15k miles) I started having a shifting issue that was concerning. During normal speed up and gear shift when set into "drive", the pickup will act like it's confused about what gear it should be in; this will always occur during the 5 to 6 gear shift. While I will want to continue accelerating to cruising speeds and overdrive, the pickup will tend to downshift instead; sometimes way down to 3rd or even 2nd gear. Other times it will just jump around between 5 and 6, before it calms down and continues into 8 and then proceed as normal. It will not act up at cruising speeds; just during normal acceleration. It does NOT seem to be as big of an issue when it is shifted manually; mainly when I let the computer shift the pickup.

It will not set a CEL on the dash, but will set 2 different codes when checked with the scanner: P0721 (Output speed sensor circuit performance) and P215c (Output shaft speed - vehicle speed correlation).

At the time (a year ago), we suspected the Output Shaft Speed Sensor; the sensor cannot be purchased separately, so the throttle body/trans computer unit was replaced and retrained. THIS SOLVED THE ISSUE... up until just recently; the same trouble codes and issues have returned.

Does anyone have any insight here?? One thing that I have noticed is that even on a cool 50 degree Minnesota day, the pickup reads trans temps in excess of 190 degrees (unloaded and highway cruising). Is this a normal temp for these pickups?

Any help is greatly appreciated. Thanks in advance. Tyler

 

[tidefan1967]

The 8spd auto actually has a heater in it for fast warm up when cold. 190 seems a little high (I think high 170's is considered normal). Sounds to me like the OS speed sensor went bad again or there's a problem with the wiring. I assume you've already serviced the transmission at least once in 175K too right.

 

[crash68]

It's normal for the 8-spd to run 180°F - 192°F pretty much all the time. Even when I'm towing an 8K lbs trailer the trans fluid will go up to 200°F and stay there.
If you start see the fluid temp spike really high and/or staying above the coolant temperature you may need to replace the transmission Thermal Management Unit. The TMU is mentioned above and has the coolant lines on it to warm the fluid and will send the fluid to the cooler(top couple rows of what is also the AC condenser).

 

[tyallis]

The 8spd auto actually has a heater in it for fast warm up when cold. 190 seems a little high (I think high 170's is considered normal). Sounds to me like the OS speed sensor went bad again or there's a problem with the wiring. I assume you've already serviced the transmission at least once in 175K too right.

Thanks for the reply

Yes... When the valve body/trans computer was replaced (again; the OS sensor is part of this unit) last fall, the trans was serviced at that time. The fluid didn't look all that bad; just looked like what you would expect after 150k. There is basically 1 large bulkhead connector that links the trans to the rest of the pickup. We pulled that apart to inspect for water, corrosion, etc. We applied some dielectric grease and snapped back together. It doesn't appear to be a connection/communication issue.
And regarding the trans temp... we also have a 2018 1500 Hemi Big Horn in our family. I drove it today bucking a headwind with an empty car trailer hooked to it (tow/haul mode, 6th gear, 2000 rpm); the trans didn't want to get over 180 degrees on a 30 mile hike. Others say that up to 200 is still normal, but I thought I would see those higher temp (if 190+ is normal) today with this pickup that still has less than 10k miles on it. ???

I am considering re-flashing the trans computer, and performing another service on it so see if anything looks suspect after this past year. Thoughts?? I just wish I could find someone or a shop that may have seen similar issues, where they could point me in the right direction.

 

[E-DAWG]

Having a similar issue I was about to ask for help on here, don't think its quite teh same but mine has been getting more pronounced over the last 18 months. On Cold start up as I head down my street it seems to downshift/rev higher somewhere between 2 and 3rd for a few seconds., after a few blocks disappears. I have found if I slowly shift through gears while its parked before leaving it is hardly noticable or at least greatly reduced. Any thoughts? 15 with 3.21 gears. I know the 3.21's have been trashed at "gear finders" and a pain but I;ve never had issues with them.

 

[tyallis]

Having a similar issue I was about to ask for help on here, don't think its quite teh same but mine has been getting more pronounced over the last 18 months. On Cold start up as I head down my street it seems to downshift/rev higher somewhere between 2 and 3rd for a few seconds., after a few blocks disappears. I have found if I slowly shift through gears while its parked before leaving it is hardly noticable or at least greatly reduced. Any thoughts? 15 with 3.21 gears. I know the 3.21's have been trashed at "gear finders" and a pain but I;ve never had issues with them.

Sure... Mine doesn't seem to be trans temp sensitive (will occur both cold and warm). This one will act up between 5th and 6th gear; I am unsure if it is "hunting" between these gears, or the converter may be locking/unlocking once it shifts shifts into 6th??? Wish I could get a visual of its current gear while NOT shifting manually. However (as mentioned above), sometimes it will tend to rapidly downshift once I get into the 5th/6th gear window. This pickup has 3.91.

Have you checked to see if there are any codes stored on your pickup? I assume you don't have a check engine light?

 

[E-DAWG]

Sure... Mine doesn't seem to be trans temp sensitive (will occur both cold and warm). This one will act up between 5th and 6th gear; I am unsure if it is "hunting" between these gears, or the converter may be locking/unlocking once it shifts shifts into 6th??? Wish I could get a visual of its current gear while NOT shifting manually. However (as mentioned above), sometimes it will tend to rapidly downshift once I get into the 5th/6th gear window. This pickup has 3.91.

Have you checked to see if there are any codes stored on your pickup? I assume you don't have a check engine light?

A buddy scanned it 3 weeks ago as I had the engine light come on and it turns out I have a bad fuel pump level sensor, the engine light hasn't come on in a week or so and I'm not too concerned with at the moment unless my fuel gauge starts going wiggy but no other codes appear. During one particular harder shift I did notice that slight metallic sound you hear when you shift into park on an incline without applying the emerg brake. Very subtle )non-scary lol sound) and sounded exactly the same. Usually the engine just slight roars (downshifts) for 3 seconds and then might do it again on block #2 but by the third block all is normal

 

[tyallis]

A buddy scanned it 3 weeks ago as I had the engine light come on and it turns out I have a bad fuel pump level sensor, the engine light hasn't come on in a week or so and I'm not too concerned with at the moment unless my fuel gauge starts going wiggy but no other codes appear. During one particular harder shift I did notice that slight metallic sound you hear when you shift into park on an incline without applying the emerg brake. Very subtle )non-scary lol sound) and sounded exactly the same. Usually the engine just slight roars (downshifts) for 3 seconds and then might do it again on block #2 but by the third block all is normal

I notice something similar to your description during the winter months; I also notice the engine's higher than normal RPM before it shifts into 2 and/or 3rd a little more violently than normal. However, I cant say I've witnessed a "metallic sound" along with it. Anyway, I've just chalked it up to the extra cool trans temps when first taking off; then once it starts to take on some temp it will behave just fine. That is... before I started experiencing my current issues. GRRR...
I'd guess that if you don't uncover any hidden codes, there probably isn't too much to worry about.