Archived lost overdrive

[RMCCAUGHREAN]

'01 2500, 4x4 diesel, auto, 85k miles used for towing and snowplowing

The truck shifted out of overdrive when towing up a hill, has not had overdrive since.

The wiring from the PCM to the trans control solenoid and on to the transmission shows good continuity.

The control voltage and the soleniod coil voltage is present at the relay socket.

relay has been replaced

The transmission shifts properly when the 3-4 shift solenoid is activated with an external voltage supply. (jumper harness)



Scanning through forums I notice that the trans fluid temp sensor was a

week link. I dont see one on this unit. At least not in the coolant line.



truck has no codes, i would appreciate any ideas.

thanks

 

[JLittle]

I know that there is a accumulator piston and spring that has something to do with 3r and 4th gear shifts ! its on the front of trans inside pan on drivers side, there are 5 screw bolts that holds it in, the piston is located above this plate with the spring too! its worth a try looking at it, the piston may be struck? good Luck!

 

[dcamilleri]

Keep looking for the trans temp switch. If I can remmember I will do a search on all data for the location.

 

[dcamilleri]

I just checked for location of transmission tempature sensor and it is located inside of the trans oil pan. It is called a transmission tempature thermistor. It communicates signals with the pcm. Hope this helps.

 

[DF5152]

does your cruise work? if not then its probably and electrical problem. a speed sensor can cause this also.

 

[RMCCAUGHREAN]

temp sensor caused overdrive inhibit

many thanks for the help.

because the local dealer could not supply or find part # for the temp sender,

i did not drop the pan to find or troubleshoot the sensor.

i opened the harness at the powertrain control module, isolated the

sensor input wire, installed 10k ohms resistance ont the circuit and

overdrive returned.

truck is back in action making $$$ and turning heads.

if anyone has part# for temp sensor, i would love to clean this up proper

asap.

thanks again



ps: dcamilleri- with the proper location and nomenclature perhaps the parts dept can locate the demon for me(?)



this round is on me-cheers

 

[dcamilleri]

DESCRIPTION















Transmission fluid temperature readings are supplied to the transmission control module by the thermistor (Fig. 238). The temperature readings are used to control engagement of the fourth gear overdrive clutch, the converter clutch, and governor pressure. Normal resistance value for the thermistor at room temperature is approximately 1000 ohms.

The thermistor is part of the governor pressure sensor assembly and is immersed in transmission fluid at all times.



OPERATION

The PCM prevents engagement of the converter clutch and overdrive clutch, when fluid temperature is below approximately 10°C (50°F) .

If fluid temperature exceeds 126°C (260°F) , the PCM causes a 4-3 downshift and engage the converter clutch. Engagement is according to the third gear converter clutch engagement schedule.

The overdrive OFF lamp in the instrument panel illuminates when the shift back to third occurs. The transmission will not allow fourth gear operation until fluid temperature decreases to approximately 110°C (230°F) .



I could not find the part number for the Transmission temp sender, but it is attached to the governor pressure sensor and located inside of the oil pan.



I tried to copy a picture of the location but I could not make it work. Hope this helps.