Electronic Transmissions and Scan Tools

Here is some abbreviations used for workshop manuals.

PCM = powertrain control module
TCC = torque converter clutch
TPS = throttle position sensor
ECT = engine coolant temperature sensor
VSS = vehicle speed sensor
(TR)PSA = transmission range fluid pressure switch assembly
TTS = transmission temperature sensor

This are used in many manuals and around technicians.

Here is a photo of automatic transmission life data. We can see various sensors and shift solenoid A, B and over run solenoid.







Wiring diagram for a PCM.















Using Holden shift chart identify which solenoids are on when:

1. When car shifts onto drive solenoid 1-2 and 2-3 are on.
2. When it shifts onto second gear automatically, solenoid 2-3 is on.
3. When shifts automatically onto third gear, none solenoids are on.
4. When shifts onto fourth gear, solenoid 1-2 is on.

So in the case of none solenoids are on the car remain in third gear constantly and can be only driven to the appropriate service center to get repaired.


Then we pick up two trouble codes out of repair manual.

First is Engine coolant temperature (ECT) signal too high. In this case car can drive on all gears except over drive i would say as my one does that until its cold for a few minutes. As transmission control module will always think that engine cold and not at the appropriate working temperature. ECT sensor can be checked on resistance matching certain engine temperature and volt dropped at the signal and ground wire and also supply voltage must be checked.

Next Vehicle Speed Sensor signal low, in this case i would say vehicle will go into fail safe mode and transmission wouldn't work properly only on that gear when both shift solenoids are off. As vehicle can see what speed is it driving it doesnt now which gear to change when. VSS can be checked with oscilloscope or a scan tool using a life data feature also wires must be checked for broken circuit.

Then we used a Hannatech scan tool on Nissan Cefire 1997 with automatic transmission.

Here is a Nissan Cefiro shift shart.

So when both solenoids are off car remain in third gear and if they are not working it still can move but only to a service station to get repaired.