BMW - A4S Diagnostic Trouble Code 40 Technical Service Information

BMW’s A4S transmission is otherwise known as the 4L30-E. This transmission is found in BMW’s 3 and 5 series models. In 3 series vehicles the transmission is referred to as the A4S/270R and the 5 series as the A4S/310R indicating torque capacity. Some model vehicles have been producing intermittent pressure control solenoid code 40. If the vehicle is equipped with an AGS version controller E34 the “Trans Program” may be displayed in the matrix (Driver Information Center). If it is equipped with the E36 version controller the transmission fault indicator may be illuminated. Cycling of the ignition switch many times restores the operation back to normal condition.

Possible Causes:
1. A bad ground or power supply to the TCM.
2. A faulty electrical circuit for the pressure control solenoid to the TCM.
3. The parameters engineered into the PROM for the TCM are too sensitive.
Step 1. Locate the TCM:
a. 1992 to 1995 318i & 325i vehicles, the unit can be found in the passenger side engine compartment behind a cover plate.
b. 1991 to 1993 525i vehicles, the unit is behind the passenger side kick panel.
c. 1994 to 1995 525i vehicles, it is the middle unit located in an electrical box in the engine compartment front of passenger side firewall.
Ground Check: Once the TCM is located, unplug the 55 pin connector and identify pin locations using Figure
2. With the ignition OFF and a DVOM set to ohms, check the ground circuit for continuity from terminal 19 in the vehicle harness connector to ground. If continuity is not observed, provide a permanent ground for wire 19. To ensure that a good ground exists, plug the harness back into the TCM. Start up the vehicle and turn on as many electrical loads as possible. Switching your DVOM to DC volts, place the negative lead to ground and probe wire 19 with the positive lead. Less than 0.3 volts should be observed. Repair ground wire as necessary. Once the ground wire check is acceptable and code 40 persists, perform the following excessive voltage check procedure.

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