fixerupper88 Posted July 14, 2020 Share Posted July 14, 2020 I have thrown in the towel on figuring out why the auto tranny on my 88 won’t shift. (The start of the Problem) on two separate occasions when I started the truck and put it into gear it hesitated before downshifting so that I can takeoff. On the third time it refused to shift at all and stayed in high gear as it is now. I own a red brick and after the third time I could no longer communicate with the TCM. Have changed trans range sensor and tried a buddy’s TCM but no improvement. Also have completed the connecter and ground refreshments as well as checked fuses. Is there any way this is a tranny solenoid issue? Any help is greatly appreciated Link to comment Share on other sites More sharing options...
Eagle Posted July 14, 2020 Share Posted July 14, 2020 Have you run the FSM diagnostic? That involves pulling the fuse for the TCM and shifting manually. I opsted it for someone not very long ago, so you should be able to pull it up. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 14, 2020 Share Posted July 14, 2020 I know you said you checked fuses, but did you check the TCU specific fuse? Its located passenger side behind the lower dash trim panel. Check out HERE for a pic, shamelessly stolen from cruiser54. Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 14, 2020 Author Share Posted July 14, 2020 I have replaced the TCM fuse even though the old one tested good. My mechanic said he was getting some power to the unit while in low gear but nothing when in Drive so he suggested replacing Trans position sensor. But no good. I can’t seem to find the FSM diagnostic you posted Eagle. But it does shift good when shifting manually. Link to comment Share on other sites More sharing options...
Ωhm Posted July 14, 2020 Share Posted July 14, 2020 3 hours ago, fixerupper88 said: I own a red brick and after the third time I could no longer communicate with the TCM. 3 hours ago, fixerupper88 said: ground refreshments Since you have NO communication with TCU and NO shifting solenoids, do you have continuity between D2_7 and battery negative terminal (B-)? Looking for a completed ground circuit back to the battery. Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 Yes I do have continuity between those two points and I am getting 12 volts all the way to the TCM. Also I can read all other system info from the ECU just no transmission Link to comment Share on other sites More sharing options...
Ωhm Posted July 15, 2020 Share Posted July 15, 2020 27 minutes ago, fixerupper88 said: I am getting 12 volts all the way to the TCM. Two (2) pins for 12vdc. C234_D14; B+ (Hot at all times) C234_D16; IGN SW (Hot with KEY ON) Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 Yep. getting 12v at both of those Link to comment Share on other sites More sharing options...
omega_rugal Posted July 15, 2020 Share Posted July 15, 2020 unplug the TCU and activate the solenoids yourself, make sure it´s no a solenoid problem Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 How do I do that. just cut 2 wires and jump the ground to ground and go to each other solenoid with the positive? I just ohmed them and got 17 on S1, 14 on S2 and 20 on S3 Link to comment Share on other sites More sharing options...
omega_rugal Posted July 15, 2020 Share Posted July 15, 2020 put the lever in OD, disconnect the TCU and apply 12v to pins c16-c15 C16 should engage 3rd C15 should engage 1st both pins engage 2nd you need a long wire to be able to do it while in motion so you can verify that the tranny is shifting Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 Well I do hear clicking when I jump both of those pins but how do I verify they are actually working? Have the vehicle running and try to make contact and see if it down shifts and begins to roll? Link to comment Share on other sites More sharing options...
omega_rugal Posted July 15, 2020 Share Posted July 15, 2020 24 minutes ago, fixerupper88 said: Well I do hear clicking when I jump both of those pins but how do I verify they are actually working? Have the vehicle running and try to make contact and see if it down shifts and begins to roll? exactly, they may click but they may not be diverting the fluid as they should Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 Ok thanks, I’ll finish that test tomorrow. Just curious would the solenoids have anything to do with why I’m not able to communicate with the TCM through the diagnostic port? Link to comment Share on other sites More sharing options...
omega_rugal Posted July 15, 2020 Share Posted July 15, 2020 20 minutes ago, fixerupper88 said: Ok thanks, I’ll finish that test tomorrow. Just curious would the solenoids have anything to do with why I’m not able to communicate with the TCM through the diagnostic port? theres no connection... or the TCU is dead... Link to comment Share on other sites More sharing options...
Eagle Posted July 15, 2020 Share Posted July 15, 2020 18 hours ago, fixerupper88 said: I can’t seem to find the FSM diagnostic you posted Eagle. But it does shift good when shifting manually. In this thread: Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 15, 2020 Author Share Posted July 15, 2020 3 hours ago, Eagle said: In this thread: OK then I already did this without knowing because I had to drive it for two days while just manually shifting it. first gear works fine then I can't really feel a shift to second but third gear works good and then I can shift it into OD and stay good until I have to slow down eventually and must start over to take off. Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 16, 2020 Author Share Posted July 16, 2020 21 hours ago, omega_rugal said: theres no connection... or the TCU is dead... Well it does shift while rolling when power is put to the solenoids Link to comment Share on other sites More sharing options...
omega_rugal Posted July 16, 2020 Share Posted July 16, 2020 9 minutes ago, fixerupper88 said: Well it does shift while rolling when power is put to the solenoids then the TCU is dead... Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 16, 2020 Author Share Posted July 16, 2020 Noooooo! well I guess the search for a good working one begins Link to comment Share on other sites More sharing options...
omega_rugal Posted July 16, 2020 Share Posted July 16, 2020 try before buy, it may be a bad harness too Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 16, 2020 Author Share Posted July 16, 2020 Now that you say that I did already try my buddy’s TCU and had the same result. Unless there was some kind of procedure needed other then just plugging it in. How do you check the harness? just find a diagram and check for continuity on each end? Link to comment Share on other sites More sharing options...
Ωhm Posted July 16, 2020 Share Posted July 16, 2020 14 hours ago, fixerupper88 said: Now that you say that I did already try my buddy’s TCU and had the same result. Try and get that Red Brick Tester (RBT) online. Both TCU B+'s & GND seem good. Check continuity between C234_C4 and D2_15 (serial data line). Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 16, 2020 Share Posted July 16, 2020 Considering what you have done so far, including swapping TCUs, I'm thinking its a bad wire somewhere. Follow Ohms recommendations. He is the genius around here for tracking down wiring problems. Link to comment Share on other sites More sharing options...
fixerupper88 Posted July 16, 2020 Author Share Posted July 16, 2020 Yes I am getting it between those two. Correct me if I’m wrong but isn’t the D1 connection for all the transmission connectivity to the RBT? Link to comment Share on other sites More sharing options...
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