G8 transmission issue

[blue98ls1]

So, since we have gotten the G8 it has been driven mostly highway miles, never sat in traffic as it is not a daily. Well, broken cars forced it out of the garage to be a daily and now I am seeing some issues. At idle, with my foot on the brake, it keeps tossing codes for the transmission speed sensor. P0716, P0717. It puts it into limp mode = max speed 25mph. When it does this, you have to be sitting for a little while, like stuck in traffic. Takes about 5-10 minutes.

 

The car has a pretty decent size cam in it. The camaro pan mod has been done recently, so fluid was changed.

 

We went into the service menu when the code came on this last time and the trans temp was around 223f. This seems kind of high to me, but I don't know much about these cars and what its supposed to be.

 

So questions are....

1 - Should I install a transmission cooler before taking apart the transmission to do this speed sensor. Could my issue be heat related?

 

2 - Could the cam being on the larger side for a stock converter be triggering something in the speed sensor? I find it weird it only does it at idle with my foot on the brake. You would think a speed sensor issue would be triggered while the car is moving.

[STEVE-O]

You have to dig into the transmission a little bit to get the harness by that sensor is known to go bad over time , I would pull the pan and I believe you have to loosen or drop the valve body to get to the sensor and harness to replace the sensor. You can test it but if I was doing all that work just to get to it to test I would personally just replace it

[wagner]

If I've learned anything in the tech articles that I've done is that heat is a huge killer of transmissions for sure.

 

I would get some high-quality fluid in there to help along with a quality transmission cooler.

 

As far as fluid goes look at the high end stuff like Royal Purple, HPL, or Driven. All of those are designed to deal with the issues heat can cause.

[Geeto67]

223 F seems high to me. Is your stock trans cooler hooked up? fans working? not plugged up?

 

The GXP came with a second trans cooler and a lot of people add them to keep temps down.

[Grudes]

I pulled your codes on GM Service Information and they are both low voltage related codes. I would check for broken wires in a connector before anything else.

 

Automatic Transmission - 5L40-E/5L50-E ( 1 Result ) DTC P0716 or P0717

Descriptor DTC P0716 Input Speed Sensor Performance DTC P0717 Input Speed Sensor Circuit Low Voltage...No DTC P0716. No TP sensor DTC P0120. No ISS DTC P0717. No OSS DTCs P0722 or P0723. No 1-2 Shift SolenoidAutomatic Transmission - 6L50/6L80/6L90 ( 1 Result ) DTC P0716 or P0717

Descriptors DTC P0716 Input Speed Sensor Performance DTC P0717 Input Speed Sensor Circuit Low Voltage

[Cordell]

The wires inside the transmission are part of the speed sensors. 220 is not abnormal on these transmissions, but I would prefer a cooler if it were mine anyway. The speed sensors are under the valve body and the TEHCM (transmission electro hydraulic control module) inside the pan, not overly hard to do but I would recommend properly installing these parts with a torque wrench, and you may need external torx plus sockets for a couple of the fasteners.

 

The other thing to consider is that speed sensor issues are also very likely when there is metal stuck to them because they are magnets. If you decide to tackle this and find any debris stuck to them then you are done and would need a rebuild.

 

Also note these require Dex6 ATF, anything else is not good for it.

[blue98ls1]

The wires inside the transmission are part of the speed sensors. 220 is not abnormal on these transmissions, but I would prefer a cooler if it were mine anyway. The speed sensors are under the valve body and the TEHCM (transmission electro hydraulic control module) inside the pan, not overly hard to do but I would recommend properly installing these parts with a torque wrench, and you may need external torx plus sockets for a couple of the fasteners.

 

The other thing to consider is that speed sensor issues are also very likely when there is metal stuck to them because they are magnets. If you decide to tackle this and find any debris stuck to them then you are done and would need a rebuild.

 

Also note these require Dex6 ATF, anything else is not good for it.

 

So if there is debris on the sensors the transmission needs rebuilt? :no:

 

I am going to install a cooler. Found the speed sensor online (GM part). REALLY hoping it doesn't need a transmission rebuild. It just got the engine rebuilt.... :fuuuu:

[Bam]

REALLY hoping it doesn't need a transmission rebuild. It just got the engine rebuilt.... :fuuuu:

 

:eek2:

[Bam]

223* does sound high to me as well, on the towing forums they start getting worried over 210* it seems...my truck runs cooler than that towing 7500lbs. Just a thought.

[Geeto67]

223* does sound high to me as well, on the towing forums they start getting worried over 210* it seems...my truck runs cooler than that towing 7500lbs. Just a thought.

 

From when I re-did my TH400 years ago, I think 225 degrees F was the upper range limit of "safe". After 225 additives in ATF start to burn off and crust up and at 240 ATF itself begins to boil and cook itself to death.

 

Something else the GTO and air-cooled motorcycles taught me is that oil temp isn't far behind. A good modern synthetic will tolerate up to 250 degrees and still hold most of it's integrity. At 260 the additives begin to break down and by 275 it's starting to cook. 1960's pontiac's overheat lights don't come on till 240-260 degrees water temp which is often pretty close to oil temp, and I once overheated the car on a cruise and collapsed a lifter because the oil started to give out in the top end. Thankfully, no other damage was done but the oil when I changed it was sparkly. Had a similar experience with the ducati when I was on the 9/11 anniversary ride and let the bike get to 315 degrees. No internal damage, but very sparkly oil.

 

To that end oil and trans temp gauges are a pretty good idea for any car that sees any kind of action beyond normal commuting.

 

As this pertains to the G8, ATF still needs some heat to work properly, so if you are going with the aux cooler, try to mount it in a location that allows it to get to temp, but might also allow it to be cooled by the fans. Maybe in front of the radiator toward the bottom (like in front of where the other trans cooler is).

 

good luck, hope it helps, and hope ytou don't have to rebuild the trans. I think what cordell is saying is with the metal shavings bit is that once you have metal shavings in the trans, there is no way to get them out other than to completely disassemble, clean, and replace the part that is creating the shavings. otherwise you will continue to have problems and eventual see trans failure.

[pontiacfreak142]

i would deffinately put a cooler on it. i just have a smaller one scott gave me on the gto and it doesnt see much above 175 ish temp wise

[aussiek2000]

Cooler was one of the first things I did. Runs 140-165 which matches what the truck runs with a factory cooler.