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Ok if they have hooked a tranx box or something similar to the truck and you dont have the problem then that means the computer is comanding this downshift activity.This does not mean the computer is bad only that some piece of data that it needs to make a decision with is faulty.There are four basic inputs that the computer needs,1 engine rpm( crank shaft sensor or tach signal from distributor)2 Engine load ( map sensor ) 3 Throttle opening / engine torque ( tps/fipl/map)4 road speed (vehicle speed sensor). my guess would be either a bad tach signal which would probaly not affect the way the engine runs or a bad map sensor.The problem with these early model E4OD transnissions was there is not much live data availiable from the onboard computer and you really need a breakout box to diagnose one of these types of problems.Good luck let me know if i can help.
P0732 - Improper Ratio for Second Gear. P0734 - Improper Ratio for Fourth Gear.
This diagnosis monitors actual gear position by checking the torque converter slip ratio calculated by TCM as follows:
Torque converter slip ratio = A x C/B A: Output shaft revolution signal from revolution sensor B: Engine speed signal from ECM C: Gear ratio determined as gear position which TCM supposes
If the actual gear position is higher than the position (2nd and 4th) supposed by TCM, the slip ratio will be more than normal. In case the ratio exceeds the specified value, TCM judges this diagnosis malfunction.
This malfunction will be caused when shift solenoid valve B is stuck open.
Gear positions supposed by TCM are as follows. In case of gear position with no malfunctions: 1 , 2, 3 and 4 positions In case of gear position with shift solenoid valve B stuck open: 4* , 3, 3 and 4 positions to each gear position above.
Symptoms: Engine Light ON (or Service Engine Soon Warning Light)
Diagnostic trouble code A/T 2ND GR FNCTN with CONSULT-II or P0732 without CONSULT-II is detected when A/T cannot be shifted to the 2nd gear position even if electrical circuit is good.
Possible Causes: - Shift solenoid valve B - Each clutch - Hydraulic control circuit
Check the transmission fluid condition and level. Dirty transmission fluid can case the solenoid to stick when changing gears causing the problem. The other thing also that can cause this a bad EPC (Electronic Pressure Control) valve or bad boost valve causing low transmission fluid pressure throughout the transmission line. At worst your clutch pack is worn and needs to be replaced. Have a transmission shop hook up a gauge to test your transmission pressure throughout the shift points to determine if your EPC and or Boost valve needs to be replaced. If the transmission shop is good they can add a 12volt 6.5 Ohm resistor inline with your ECM signal to the EPC to firm up the transmission shift to keep the transmission from burning up the clutch packs in the future. Good luck and keep me posted.
P1529 indicates that your TCM asked the ECM to turn on the check engine lamp.
The range switch and the output speed sensors are the items that are
abnormally affecting the operation of the transmission. The diagnostic
logic in your computer can distinguish these issues from one another,
so you'll definitely want to do both. You have no diagnostic code for
the input speed sensor (P0715) listed, so I have made no recommendation
to replace it. In my opinion, it's not a labor-intensive repair, so I
wouldn't recommend replacing it unless you have reason to believe it's
DTC - P0720 (OUTPUT SHAFT SPEED SENSOR SYSTEM)
Code No. P0720 Output shaft speed sensor system
If the output from the output shaft speed sensor is continuously 50%
lower than the vehicle speed for 1 second or more while driving in 3rd
or 4th gear at a speed of 30 km/h or more, it is judged to be an open
circuit or short-circuit in the output shaft speed sensor and
diagnostic trouble code No. P0720 is output. If diagnostic trouble code
No. P0720 is output four times, the transmission is locked into 3rd
gear or 2rid gear as a fail-safe measure.
Malfunction of the output shaft speed sensor
Malfunction of the transfer drive gear or driven gear
Malfunction of connector
Malfunction of the TCM
DTC - P0715 (INPUT SHAFT SPEED SENSOR SYSTEM)
Code No. P0715 input shaft speed sensor system
If no output pulse is detected from the input shaft speed sensor for 1
second or more while driving in 3rd or 4th gear at a speed of 30 km/h
(19 mph) or more, it is judged to be an open circuit or short-circuit
in the input shaft speed sensor and diagnostic trouble code No. P0715
is output. If diagnostic trouble code P0715 is output four times, the
transaxle is locked into 3rd gear or 2nd gear as a fail-safe measure.
Malfunction of the input shaft speed sensor
Malfunction of the underdrive clutch retainer
Malfunction of connector
Malfunction of the TCM
It sound like your transmission is on a limp mode and you only have 3rd and second. The default will be at 3rd, but to can place the gear shifter to 2nd to get started. Note; that your going to be putting extra stress on the converter so don't push it to hard or your going to burn that out which will be a more costly repair. Common cause to this problem is a faulty wire harness or a bad shift solenoid which is an average cost of $20.00, so take is easy till you can limp it to a Transmission shop. $150.00 repair is much better then a $1,900 repair. Good luck and keep me posted, be glad to help you get your truck running 100% again soon. Almost for got, try resetting the ECM by turning the ignition to the on position (Engine not running) and pull the ECM fuse out for 30 seconds and placing it back in, start the engine. The engine may stall but let it, it's just relearning the sensor and then go for a test drive after 1 min if idling. This may get your transmission reset if there is not electrical or mechanical problems.
There are to many things that can cause this problem, best thing to is go get the ECM scanned for DTC codes at a transmission shop or Auto zone or Parts Source since they scan for free.
The ECM should have DTC code in it's memory on how the transmission is Performing and have the Transmission line tested for Fluid pressure.
Good luck and hope this helps. Oh and also ways check with more then on transmission shop if there tell you that you need a new Transmission,
It could be a simple as the transmission filter falling off causing the lost of transmission fluid pressure. Check the transmission fluid too.
Code 0753 means Transmission 3-4 shift solenoid or transmission relay circuit problem. The PCM (engine computer) is seeing an incorrect input electrically for the gear or speed it should be seeing. You will need to find a qualified transmission shop to diagnose the problem. Possible causes for the trouble code start with worn/dirty fluid, electrical repairs & transmission overhaul.