Toyota and Lexus vehicles equipped with either the 4 speed front wheel drive U140/240 transmission or the 5 speed front wheel drive U150/250 transmission may exhibit a loss of high gear (4th or 5th). In both cases the S4 solenoid needs to be energized by the computer for this shift into high gear to take place.
There is a variety of transmission and temperature related codes or, malfunctions with no codes yet set that can cause this condition. To verify a shift or a no shift command by the computer is done simply by monitoring the single wire going to the S4 solenoid with a volt meter. If system voltage is observed at the time a shift into high gear should take place yet the shift didn’t occur, there is a problem inside the transmission.
If system voltage is never seen, the computer did not command the shift. If there are no codes present, inspect the Transmission Range sensor and all temperature sensor readings for proper operation.
If there are codes set, resolve them. This includes any engine performance diagnostic trouble codes, especially the Knock Sensor. This is the number one cause for this complaint and is often times overlooked as being insignificant to the transmission’s operation.
U140-240 S4 Solenoid Test Procedure:
Locate the solenoid 10 pin case connector which faces towards the front of the vehicle. Identify the S4 solenoid wire. Probe a volt meter lead into the wire located in terminal 8 at the case connector with the positive lead. Connect the negative lead to a good engine ground. Bring the vehicle up to 50-55 mph and look for battery voltage on the volt meter. If there is "No" voltage, and the vehicle has engine performance related codes, they will need to be fixed first. If there is battery voltage at 50-55mph, this would indicate that the problem is inside of the transmission, as the PCM is commanding 4th gear, repair as necessary.
U150-250 S4 Solenoid Test Procedure:
Locate the solenoid 13 pin case connector which faces towards the front of the vehicle. Identify the S4 solenoid wire. Probe a volt meter lead into the wire located in terminal 3 at the case connector with the positive lead. Connect the negative lead to a good engine ground. Bring the vehicle up to 50-55 mph and look for battery voltage on the volt meter. If there is "No" voltage, and the vehicle has engine performance related codes, they will need to be fixed first. If there is battery voltage at 50-55mph, this would indicate that the problem is inside of the transmission, as the PCM is commanding 5th gear, repair as necessary.
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