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4L80/85E Transmissions. 6L90 Transmission Discuss the 4L80/85E transmissions found in the 6.2/6.5L equipped vehicles and Duramax equipped vans. 6L90 discussion.

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Old 04-28-2019, 07:33 PM   #1 (permalink)
yukon94Diesel
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No shifting out of first on some cold starts

1. State model, year of vehicle and mileage:
1994 GMC Yukon 6.5 Diesel 220750 miles

2. How long did you own the truck? Recent purchase?
Have had the truck for about 9 months now.

3. Any service engine light: yes/no. Intermittant check engine light?
This is called CEL or MIL

No CEL

4. Fluid level okay with the engine and transmission warm? Check on
a level surface?

Fluid level is fine

5. Have you retrieved Codes? AKA DTCs Diagnostic Trouble codes.

No codes are present

6. Fluid color and smell? Red or Brown does the fluid smell burnt?

Fluid is a pink color and no burnt smell.

7. Speedometer reading correctly at the appropriate speed? Are the tires the within OEM specifications and size? Use your GPS and verify speed. electronic transmissions remember?

Speedometer is about 10% off. Currently using 31" tires.

8. Is the transmission shifting normal? Is it shifting hard? Do recall the shifting symptoms or any shifting changes before or after the check engine light or after you retrieved codes.

Transmission seems to shift normally, shifts are smooth and not hard.

9. Did you or anyone else conduct any kind of maintenance to the vehicle recently?

Only oil changes, diff fluid changes, fuel filter change, lift pump change.

10. Can you explain the type of driving? Heavy towing? Snowplowing?

Mostly driving around town, highway driving, no heavy towing. Only using dirt bike hitch carrier.

11. Typical weather. Arizona hot mild winters? Minnessota cold. Please explain.

Western washington temps. Winters no colder than mid 20s, summers no higher than 90s.

10. Any problems with driver commanded/selected shifting into any gear?
ie.. 1st, 2nd, 3rd, 4th, Rev?

No, all driver commanded gears work fine.

8. Describe symptoms: Does the transmission refuse to shift in first? Will it shift into second and just stay in second gear?

Truck will usually not shift out of first after a cold start. Sometimes it will work just fine. Will proceed to shift normally if I restart the truck and continue driving.

8a. TCC Locking? Is the transmission slipping in any gear?

No slipping, TCC locks up fine.

8b. Is the transmission shifting into all FWD gears? At the
normal RPMs while the shift selector is in drive? Is it shifting later
than usual?

After restart transmissions seems to shift into all forward gears normally.

Can your vehicle shift into all gears?
If you have a tachometer can you "notice" all forward gears shifting if you are not sure if the transmission is shifting?

It will shift into all gears fine after restarting.



This is an extremely odd issue and from what I can tell nobody has the exact same symptoms I am experiencing. I have replaced the input speed sensor and there was no change. I've been living with this issue since shortly after I got the truck. Hoping there's a transmission wizard here with an idea.

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1994 GMC Yukon 6.5 Diesel

Last edited by OkDually; 04-28-2019 at 08:59 PM. Reason: prefix/sig
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Old 04-28-2019, 09:09 PM   #2 (permalink)
Glagulator
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Location: Very south TEXAS, Formerly Wisconsin
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Welcome.
Have you tried manually shifting thru the gears before re-starting, while it will not auto upshift?

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There are 10 kinds of people in this world; Those who understand binary and those who don't.

99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine harness, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 04-30-2019, 02:45 PM   #3 (permalink)
yukon94Diesel
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Quote:
Originally Posted by Glagulator View Post
Welcome.
Have you tried manually shifting thru the gears before re-starting, while it will not auto upshift?
I've tried going through all the forward gears while this is happening and it still wont shift up.
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Old 04-30-2019, 03:24 PM   #4 (permalink)
Glagulator
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Join Date: May 2005
Location: Very south TEXAS, Formerly Wisconsin
Posts: 3,526
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Sounds electrical to me. The ISS you replaced is the same as the VSS.
Try replacing the VSS with the old ISS if you still have it or get a new one.
Check the connectors at the tranny real close for broken wires, wires pulled from the terminals, still in the connector but broken. Make sure the VSS jumper harness, short harness from VSS to inline connector is ok and plugged in.
If you have a different PCM available, 94 or 95, you could give that a try if the VSS and wiring/connectors are ok.
__________________
There are 10 kinds of people in this world; Those who understand binary and those who don't.

99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine harness, PMD to bumper...
95 C1500 Suburban 6.5td rebuild tranny, convert to DB2, replacing as many parts as I can.
96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73
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Old 04-30-2019, 06:34 PM   #5 (permalink)
yukon94Diesel
Gear Grinder
 
Join Date: Apr 2019
Posts: 4
iTrader Score: 0 reviews

Quote:
Originally Posted by Glagulator View Post
Sounds electrical to me. The ISS you replaced is the same as the VSS.
Try replacing the VSS with the old ISS if you still have it or get a new one.
Check the connectors at the tranny real close for broken wires, wires pulled from the terminals, still in the connector but broken. Make sure the VSS jumper harness, short harness from VSS to inline connector is ok and plugged in.
If you have a different PCM available, 94 or 95, you could give that a try if the VSS and wiring/connectors are ok.
I'll replace the VSS and take a look at the wiring. No PCM available to test but i'll cross that bridge if it comes to it.

Thanks!
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1994 GMC Yukon 6.5 Diesel

Last edited by OkDually; 04-30-2019 at 07:12 PM. Reason: sig
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Old 05-08-2019, 03:00 PM   #6 (permalink)
yukon94Diesel
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Well I replaced a couple of worn battery terminals and it appears that the negative on my passenger side battery wasn't connected. I had been running my truck with only the drivers side battery hooked up. Replacing the terminal made the truck start so much easier than it did before. Since I fixed that I haven't had the shifting issue.
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