If you are not aware, Honda and Acura transmissions do not shift properly while on a lift with the wheels off the ground. In fact many shops have lost time and money thinking there is a transmission problem when there is not. The transmission exhibits erratic shifts conditions that otherwise would not occur if driven on the road. The transmission would be needlessly removed numerous times and computers would be changed to no avail. All this time, had they driven it on the road, the transmission would have operated flawlessly.
Recently, a 2003 Honda CRV with an MCVA transmission was rebuilt and installed into the vehicle. The tech knew not to drive the transmission on the lift. So he filled the unit with all 4 wheels on the ground. When he placed the selector lever into reverse to back off the lift he had no movement. So he placed the selector lever back into Park and checked the level. It was full. He tried it again and still no reverse. This time the MIL illuminated. After placing the transmission back into Park he checked for codes and pulled P0780, a mechanical problem in the hydraulic control system.
Honda suggests to record all freeze data as well as to review general troubleshooting information before troubleshooting. In other words, get your head around the basics before overshooting the troubleshooting process. It then says to obtain seven replacement solenoids, the three pressure control solenoids A, B and C and 4 shift solenoids, A, B, C and E.
The first set of solenoids to replace is all 3 of the pressure control solenoids. It then says to erase the code by pulling the number 6 ECU 15 amp fuse from the under-hood fuse/relay box for more than 10 seconds. Afterwards, drive the vehicle forward for several minutes. Do this 6 times and if code P0780 returns change all the shift solenoids.
Well, these 3 pressure control solenoids were replaced yet they still had no reverse and P0780 returned. So, all 4 shift solenoids were replaced. Can you suppose what happened? Of course, no reverse. This time however, the selector lever was placed into drive and it engaged. They then placed the selector lever into reverse and it moved.
When the vehicle was driven it shifted badly. Code P0780 remained yet codes P0715 and P0720 also emerged. These are codes for problems with the mainshaft and countershaft speed sensor signals. What a mess!!! But here is where the problem lays, the speed sensors were accidently cross connected. The harness with the black connector is plugging into the mainshaft speed sensor while harness with the blue connector is plugging into the countershaft speed sensor.
A tip here is to view these signals in a scan tool while in park or neutral. The mainshaft sensor should have a reading while the countershaft should read 0. If the mainshaft reads 0 while the countershaft has a high rpm reading, the sensors are cross connected. The computer will prevent a reverse engagement deliberately as it thinks the vehicle is moving forward at the time of engagement.
If the selector lever is placed into Drive, with the foot on the brake, both sensors will no read 0 (providing the clutch can hold). With 0 readings on both sensors, a reverse engagement will occur from the drive position.
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