Only two weeks to the big trip and transmission trouble.

[comfun1]

2005 GMC 2500 4x4 less than 100k miles. Not driven on a regular basis. I got in it yesterday backed up shifted to drive and with each shift it slams into gear instead of shifting smoothly. Never had a hint of a problem before. Hoping to find a transmission shop that can get right on it today.

[SKnight]

Probably the pressure control solenoid stuck maxing out the pressure. What engine/trans is it?

[comfun1]

6.0 liter with auto transmission.

[TURBS]

My 05 6.0 auto had zero issue's in 200,000 miles.
I changed fluid and filter twice.

"sabre owners united!"


turbs

[SKnight]

Originally Posted by comfun1

6.0 liter with auto transmission.

Is it a four speed or a five speed? The four speed will be a 4L80E and a five speed will be the Allison LCT1000.

If the only issue is the hard shift chances are the trans is fine, it's either the pressure control solenoid as I mentioned or the computer is maxing the pressure out on purpose.

Should be an easy fix, but I forgot to ask, is the check engine light on?

[comfun1]

Ok, the check engine light never came on. I took it to a tranny shop yesterday and this is what I found out. When the mechanic connected his scanner he found a P1810 code. He said he had never seen this code before so he looked it up and this is what he found.

"A 4L80E may intermittently set DTC P1810 and exhibit harsh shifts. Freeze frame/ fail records may show the vehicle was in reverse and the P1810 set shortly after a cold start. The vehicle may also have not been started for an extended period of time.
Recommendation/Instructions:
This condition may be inadvertently induced by starting the vehicle and immediately shifting the transmission into a drive range or reverse. If the PCM does not see a PRND43 input from the transmission fluid pressure switch before the customer shifts into a drive range or reverse, the PCM will assume the TFP is malfunctioning because the PCM did receive a signal from the PRND43 switch and set the code P1810. This condition would occur more easily if the vehicle has not been started for an extended period of time because of torque converter drain back. DTC P1810 does not turn on the MIL the first failure, but does store the code and it commands maximum line pressure. The customer will probably notice only the harsh shift.
Currently, there is no fix for this condition. The dealer can advise the customer to start the vehicle and allow it to run for a few seconds before selecting reverse or selecting D4 before reverse."

Apparently all is well and normal, I hope.

[Brother Les]

This condition would occur more easily if the vehicle has not been started for an extended period of time because of torque converter drain back.

Now you know.... torque converter drained out....

Currently, there is no fix for this condition. The dealer can advise the customer to start the vehicle and allow it to run for a few seconds before selecting reverse or selecting D4 before reverse."

Yes there is a fix..... drive your truck more often .....


(good to know all is ok)

[SKnight]

I actually saw that code a lot back in the GM days and the diagnosis is spot on. The ECM assumes there's a pressure leak and commands that high line pressure to protect the transmission.

Good to hear there's actually nothing wrong!

[TURBS]

Good news!

"sabre owners united!"


turbs

[Aca651]

I'm not a big fan of additives, but go to a local parts store, I've even seen this sold at Walmart. Lucas transmission additive. I had a 98 expedition with the hard shift as you have described it did wonders. We recommend it often at the shop I work in. It seems to be a great product and I think you will be happy with the results.

[TURBS]

Actually gm is a big advocate of BG products.

TURBS

"SABRE OWNERS UNITED"