Avalanche Owners Zone > Problems: Drivetrain & Steering

Bad DTC Transmission Codes! Help!

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Hello I am new to the site but have been watching for a few days I need help.
For the past few days I have been noticing (intemittant) very slow acceleration from a stop. Almost feels like brake drag etc. Well then Wed. the Service Engine soon light came on. The engine is running great no misfires very smooh etc. So I did an overnight elec. reset. and the light stayed off for a day and a half (75miles) now it is back on on my way home...so I went to the auto parts store and read the codes :
P0740 - TCC enable solenoid circuit electric
P0785 - 3 - 2 shift solenoid circuit electrical
P1860 - TCC PMW Solenoid circuit electrical
Maybe some of you could shed some light on what is wrong and what this means cost wise? Should I go to the dealer for this or can a trans shop do this???
Thanks In Advance

Dealer, or trans shop could both do it. Dealer may be better, as some trans shops may sell a rebuild and it may not be needed.!? I don't necessarily like recommending the dealer, however, they would probably be more experienced and seen more of these problems. GM has valve body and solenoid problems with a lot of they're transmissions. Not cheap though, as we just did one in a Pontiac Montana to the tune of $900. At that price, the customer was actually considering having a reman put in for more $ as it had 100K on it.

In addition,

Don't be surprised that it's the ignition switch.

Measure voltages at the IGN-0 and IGN-1 fuses. More detail if I knew the year model you didn't provide.

Different faults occur with ign switch failures. It depends on the "pole" of the switch. In the case of the transmission solenoids. The ign switch contact that feeds the pcm & solenoids could be too resistive to pass the current necessary to actuate them.

Alternately, you could have a corroded wiring connector on the trans. Corrosion (water/electrolysis) could be bad enough that the connections are too poor to pass the needed current.

And shift problems can even be traced back to the MAF sensor, where over-oiling of an aftermarket air filter affects the heated wire. In turn, the calibration is far off and drive train components receive erroneous data.

There are TSB's on these things, but to proceed, we would better assist you if we knew what model & year you had!

I did forget...It is a 2002  built 01/02 - Z71 4x4 - 1500 with 65K on it. The family and I are scheduled for a trip up north Aug.8th I need it to pull the camper about 3000lbs....Yipes

See if your trans fluid is burned. Usually 02's don't have as much trouble with that - (trans cooler) but that's not always a saving grace. Leave it alone if it's burned. Often a flush of burned or dirty fluid can provoke a soon-after trans death! Instead, service it (full R&R and disassemble) later. and make sure it's kept as cool as possible meanwhile.

If it's clean, not to worry, refer to this for the keyswitch...

Here's the TSB:

Document ID# 1556712
Chevrolet Avalanche
Malfunction Indicator Lamp (MIL) On, Transmission Stuck in Second or Third Gear, Instrumend Cluster Inoperative (Replace Ignition Switch) #01-07-30-002D - (Oct 19, 2004)

2004-2005 Buick Rainier

1999-2000 Cadillac Escalade

2002-2005 Cadillac Escalade, Escalade EXT

2003-2005 Cadillac ESV

1997-1999 Chevrolet Full-Size Pickup, Suburban, Tahoe (Old Style)

1997-2005 Chevrolet Blazer, Corvette, Express, S-10

1999-2005 Chevrolet Silverado (New Style)

1999-2005 Chevrolet Blazer RH Drive (Export)

2000-2005 Chevrolet Suburban, Tahoe

2002-2005 Chevrolet Avalanche, TrailBlazer, TrailBlazer EXT

2004-2005 Chevrolet Colorado

1997-1999 GMC Sierra, Suburban, Yukon (Old Style)

1997-2001 GMC Jimmy

1997-2005 GMC Savana, Sonoma

1999-2005 GMC Sierra (New Style)

2000-2005 GMC Yukon, Yukon XL

2002-2005 GMC Envoy, Envoy XL

2004-2005 GMC Canyon, Envoy XUV

1997-2004 Oldsmobile Bravada

2004-2005 Pontiac GTO

2003-2005 HUMMER H2

with 4L60-E, 4L65-E, 4L80-E or 4L85-E Automatic Transmission (RPOs M30, M32, M33, MT1, MN8)

This bulletin is being revised to update model years, add additional models and 4L80/85 Transmission Information. Please discard Corporate Bulletin Number 01-07-30-002C (Section 07 -- Transmission/Transaxle).


Some customers may comment on one or more of the following conditions:

    * The Malfunction Indicator Lamp (MIL) is ON.
    * The transmission is defaulted to second gear (4L80/85-E).
    * The transmission is defaulted to third gear (4L60/65-E).
    * The instrument cluster is inoperative.

Upon investigation, one or all of the diagnostic trouble codes (DTCs) P0740, P0753, P0758, P0785, P0787, P0973, P0976, P1860, P2761, P2764 and P2769 may be set depending on the vehicle.


The most likely cause of this condition may be a loss of voltage to the transmission on circuit 1020. This loss of power may be caused by an open in the ignition switch. This condition may also be the result of an incorrect installation of an aftermarket electronic device such as a remote starter or alarm system.


With the ignition switch in the RUN position, test for battery voltage at the IGN 0 fuse (All Av's to date).

If battery voltage is present at the fuse, inspect the ignition voltage circuit between the fuse and the transmission for possible opens. If battery voltage is not present at the fuse, replace the ignition switch using the Ignition Switch Replacement procedure in the Steering Wheel and Column sub-section of the applicable Service Manual. Refer to group number 2.188 of the parts catalog for part description and usage.

If the vehicle is equipped with an aftermarket electronic device and the DTCs are being set when the device is being used, verify that the appropriate fuse listed above is being supplied battery voltage during operation. If voltage is not present at this fuse, these DTCs will be set due to lack of voltage at the solenoids. This condition is most likely to occur with an incorrectly installed remote starting system. If this is the case, refer the customer to the installer of the system for corrections.


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