transmission issue

[dfdsc68]

hey everyone, new here hoping im posting in the right place

I have a 2002 2500 lb7 stock with a fass fuel system

recently I have been having an intermittent issue with my trans. especially in wet weather it seems. the transmission temperature guage on the dash will flatline and 2-1 downshift is very harsh. if I shut the truck off and restart it will clear and be normal, with normal temp on gauge.

I recall it having a code somewhere along the lines of transmission temp sensor communication error

like I said it comes and goes. I have checked the harnesses for cuts and whatnot

any ideas? I have a big trip to north Carolina coming up I want to make sure im okay to go

 

[zakkb787]

From my understanding. The harsh downshift is a common issue with these. And the trans temp is normal with lots of miles too. Probably a stepper motor

 

[dfdsc68]

its just weird that once that guage looses temp the trans acts up

 

[THEFERMANATOR]

Get a scanner on it and see what the trans temp is being read from the trans temp sensor. Steppers fail in 03-05 trucks often, but an 02 truck does not use steppers, but instead uses air cores for the gauges(very reliable and rarely fail). My bet is something is up with the trans temp sensor circuit, and the TCM adjusts the TAPS and shift times for cold transmission operation as cold fluid flows through a trans much differently than hot fluid, so it compensates. If it is reading the incorrect fluid temp, then it can correct wrong, and throw the shifts off. The 2-1 downshift is a rough shift to begin with as the C5 pack is large in comparison to the others, so even the slightest miscalculation in TAPS can make it slam pretty hard.

 

[dfdsc68]

Get a scanner on it and see what the trans temp is being read from the trans temp sensor. Steppers fail in 03-05 trucks often, but an 02 truck does not use steppers, but instead uses air cores for the gauges(very reliable and rarely fail). My bet is something is up with the trans temp sensor circuit, and the TCM adjusts the TAPS and shift times for cold transmission operation as cold fluid flows through a trans much differently than hot fluid, so it compensates. If it is reading the incorrect fluid temp, then it can correct wrong, and throw the shifts off. The 2-1 downshift is a rough shift to begin with as the C5 pack is large in comparison to the others, so even the slightest miscalculation in TAPS can make it slam pretty hard.

Thanks for the response i dont have a scan tool handy i just remember it being a communicstion error with the temp sensor. Should i do anything at this point

 

[THEFERMANATOR]

Thanks for the response i dont have a scan tool handy i just remember it being a communicstion error with the temp sensor. Should i do anything at this point

Without knowing basic info like what the trans temp is when it acts up, theres noth8ng I would reccomend doing. I don't know of any temp sensor communications error codes for the trans. The temp sensor is a basic thermister sensor, one side to the PSM common, and the other side connectsto the TCM trans temp sensor sense wire. Need to know the actual P code to help point you in the right direction.

 

[dfdsc68]

Without knowing basic info like what the trans temp is when it acts up, theres noth8ng I would reccomend doing. I don't know of any temp sensor communications error codes for the trans. The temp sensor is a basic thermister sensor, one side to the PSM common, and the other side connectsto the TCM trans temp sensor sense wire. Need to know the actual P code to help point you in the right direction.

Just plugged it in. Code P0711 transmission fluid temperature sensor A circuit range/performance

 

[dfdsc68]

Its very intermittant as i said, im wondering if its a harness issue somewhere? Internal or external. Any where i should poke around and look?

 

[THEFERMANATOR]

I would check the harness for chafes, but theres a good chance the trans temp sensor has failed as it's just a thermistor inside the pressure switch manifold. I believe allison sells the the PSM for arount $70. The hardest part is dropping the pan to change it.

 

[Budneeds2beers]

I want to say i just read another thread like this and i also want to say mike chimed in and recomended to buy a scanner and scan it. Said it would be a five min test (dont quote me in this as your situation is/maybe different.). I understand your position on dropping that kind of coin on a tool that would rarely be used. Like you i am also one of "THOSE" people. So i myself plan on keeping this truck for some time and buying another so it would be a wise investment. While trolling most of these post reading all the time thats the first thing any senior member asks. "Do you have a good scan tool" maybe mike might chime in but also i think he might have read this post/problem and thought no scanner not really any codes cant help the guy. (Not saying what he did or didnt do) but thats how common sense would see it. Sorry not trying to grill you friend.

Do you have a secondary guage set? I just got edge insight and plugged it into obd2 and a problemed fallowed with a no read scenario so i know its not the guage just the input sensor.

 

[zakkb787]

Agreed with bud. My gauge flies all around at times randomly but it reads just fine on my edge.

 

[dfdsc68]

I want to say i just read another thread like this and i also want to say mike chimed in and recomended to buy a scanner and scan it. Said it would be a five min test (dont quote me in this as your situation is/maybe different.). I understand your position on dropping that kind of coin on a tool that would rarely be used. Like you i am also one of "THOSE" people. So i myself plan on keeping this truck for some time and buying another so it would be a wise investment. While trolling most of these post reading all the time thats the first thing any senior member asks. "Do you have a good scan tool" maybe mike might chime in but also i think he might have read this post/problem and thought no scanner not really any codes cant help the guy. (Not saying what he did or didnt do) but thats how common sense would see it. Sorry not trying to grill you friend.

Do you have a secondary guage set? I just got edge insight and plugged it into obd2 and a problemed fallowed with a no read scenario so i know its not the guage just the input sensor.

Yes i plugged it in with scan tool and got code P0711 as stated above. I have my edge and the trans temp would also have no reading on that as well

 

[Budneeds2beers]

Well i would say some sort of fault. Wether it be a chafed wire or a bad input. Personally i would say input just because if you had a chafed wire, when you wiggled the loom you will get a reading near 5v when cold. If you just dont then i would say input from inside trans. Maybe ohm it and see what its doing? Check for fault from plug connector to chassis/ground and check the plug.... maybe you'll have some luck that way. I belive the sensor gets a 5v signal through the trans and as the temp rises it drops voltage down. So if your not getting any voltage back its sensing that the trans is over temp.

 

[dfdsc68]

Well i would say some sort of fault. Wether it be a chafed wire or a bad input. Personally i would say input just because if you had a chafed wire, when you wiggled the loom you will get a reading near 5v when cold. If you just dont then i would say input from inside trans. Maybe ohm it and see what its doing? Check for fault from plug connector to chassis/ground and check the plug.... maybe you'll have some luck that way. I belive the sensor gets a 5v signal through the trans and as the temp rises it drops voltage down. So if your not getting any voltage back its sensing that the trans is over temp.

Roger that. Ill check it out. Thanks!

 

[Mike L.]

Roger that. Ill check it out. Thanks!

12V system. 5V=no move.
There is nothing in the Alli that is 5V except a bad ignition switch.

 

[Budneeds2beers]

Ahhh. Stand corrected thanks mike.

 

[THEFERMANATOR]

12V system. 5V=no move.
There is nothing in the Alli that is 5V except a bad ignition switch.

Not to argue with you, but isn't the thermistor feed a 5v reference wire from the TCM pulled to ground via the thermister to give a temp reading? All of the solenoids are 12 volts from the switched ignition switch feed from the fuse panel inside the cab, but last I checked sensor wires like the trans temp sensor were still 5 volts.

 

[THEFERMANATOR]

Found a copy of the GM flow chart for diagnostics of a P0711 DTC code with an ALLISON transmission.

DTC P0711
Circuit Description
The transmission fluid temperature (TFT) sensor is a part of the pressure switch manifold (PSM) assembly, and is located in the transmission oil pan. The TFT sensor is a thermistor, which changes value based on the temperature of the transmission fluid. The sensor has a negative–temperature coefficient. This means that as the temperature increases, the resistance decreases, as the temperature decreases the resistance increases. The transmission control module (TCM) supplies a 5 volt reference voltage signal to the TFT sensor and measures the voltage drop in the circuit. When the transmission is cold, the sensor resistance is high and the TCM detects high signal voltage. As the fluid temperature warms to a normal operating temperature, the resistance becomes less and the signal voltage decreases. The TCM uses this information to control shift quality and torque converter clutch (TCC) apply.

DTC P0711 is a type B DTC.

Conditions for Running the DTC
•DTC P0712, P0713, P0716, P0717, P0721, and P0722 are not active.
•The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
•Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
•The engine has been running for 2 seconds.
•Engine speed is above 450 RPM and output speed is above 100 RPM.
•The TFT is in the range of −35°C to +149°C (−31°F to +300°F).
Conditions for Setting the DTC
DTC P0711 sets when the TCM detects one of the following conditions:

•The TCM detects a temperature change that is below a set limit when compared to samples of the minimum and maximum temperature values.
•The TFT has an unrealistic temperature change of greater than 10°C (50°F) for 10 occurrences.
•The temperature from startup decreases 40°C (104°F) or greater within a duration of 6 seconds or greater.
Action Taken When the DTC Sets
•The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
•The TCM freezes shift adapts.
•The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.
•The TCM stores DTC P0711 in TCM history.
•The TCM inhibits TCC engagement.
Conditions for Clearing the DTC
A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids
•The TFT should rise steadily during warm-up cycles, then stabilize.
•DTC P0218 may set after DTC P0711 has set. Follow the diagnostic table for DTC P0711 before proceeding to the diagnostic for DTC P0218.
•Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
– A bent terminal
– A backed-out terminal
– A damaged terminal
– Poor terminal tension
– A chafed wire
– A broken wire inside the insulation
•When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
•You may have to drive the vehicle in order to experience a condition.
•An open condition at circuit 2762 may allow a ground path internally through circuit 2471. If this occurs, the TCM sees a temperature that appears to be within normal operation, approximately −22°C (−7.6°F), and initially a code will not be set. However, the transmission will still inhibit shift adapts and TCC operation. It may take several minutes before P0711 code is set to indicate a failure.
Test Description
The numbers below refer to the step numbers on the diagnostic table.

4.This step tests 5 volt reference.
6.This step tests the TFT sensor and internal wiring harness.
7.This step tests the resistance of the TFT sensor.
DTC P0711 Step
Action
Value
Yes
No

Schematic Reference: Automatic Transmission Controls Schematics

1
Did you perform the Diagnostic System Check – Automatic Transmission?
—
Go to Step 2
Go to Diagnostic System Check - Automatic Transmission

2
Measure the transmission fluid level.

Refer to Transmission Fluid Level and Condition Check.

Is the transmission fluid level correct?
—
Go to Step 3
Go to Transmission Fluid Level and Condition Check

3
 1. Install the scan tool.
 2. Turn ON the ignition, with the engine OFF.
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

 3. Record the DTC Freeze Frame and Failure Records.
 4. Clear the DTC.
 5. Select TFT on the scan tool.
 6. Drive the vehicle and look for an unrealistic TFT reading.
Is the TFT reading at or below the specified value?
1.5°C (2.7°F)
Go to Step 4
Go to Diagnostic Aids

4
 1. Turn the ignition OFF.
 2. Disconnect C2 connector (RED) at the TCM.
 3. Install the J 39700 breakout box and the J 43799 breakout box adapter at C2 connector.
 4. Turn ON the ignition, with the engine OFF.
 5. Use a DMM, measure voltage at C2 connector (RED) terminal 10 and terminal 20.
Is voltage within the specified value?
5 V
Go to Step 5
Go to Step 11

5
 1. Turn the ignition OFF.
 2. Using a DMM, measure resistance at C2 connector (RED) terminal 10 and terminal 20.
Is the resistance within the specified value?
3,490 Ω @ 20°C (68°F)

177.9 Ω @ 100°C (212°F)
Go to Diagnostic Aids
Go to Step 6

6
 1. Turn the ignition OFF.
 2. Disconnect the transmission 20-way connector.
 3. Using a DMM, measure resistance at the transmission side 20-way connector terminals G and H.
Is the resistance within the specified value?
3,490 Ω @ 20°C (68°F)

177.9 Ω @ 100°C (212°F)
Go to Step 8
Go to Step 7

7
 1. Remove the oil pan.
 2. Disconnect the PSM from the internal wiring harness.
 3. Using a DMM, measure pressure switch manifold (PSM) resistance at terminals E and F.
Is resistance within the specified value?
3,490 Ω @ 20°C (68°F)

177.9 Ω @ 100°C (212°F)
Go to Step 9
Go to Step 10

8
Repair the engine wiring harness. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
—
Go to Step 12
—

9
Replace the AT internal wiring harness. Refer to Wiring Harness Replacement.

Did you complete the replacement?
—
Go to Step 12
—

10
Replace the PSM. Refer to Pressure Switch Manifold Replacement.

Did you complete the replacement?
—
Go to Step 12
—

11
Important: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.

Replace the TCM. Refer to Transmission Control Module Replacement.

Did you complete the replacement?
—
Go to Step 12
—

12
Perform the following procedure in order to verify the repair:

 1. Clear the DTC.
 2. Using the scan tool, monitor the TFT.
 3. Drive the vehicle under normal operating conditions. Watch for significant changes in TFT.
 4. Select Specific DTC.
 5. Enter DTC P0711.
Has the test run and passed?
System OK
Go to Step 1

 

[Budneeds2beers]

Nice.

 

[dfdsc68]

Thanks for everyones input. I changed my temp sensor this weeked, checked all the wiring and so far so good!