BMW 740iL Speedometer is not working Inspection at your home or office.

How it's done:

A mechanic will first examine the vehicle using a code reader/scanner to review any error codes or Check Engine light the vehicle may have produced. By connecting to the vehicle’s ECU, the mechanic can get a better idea of what components may have failed.

If the mechanic believes that the speed sensor has failed, he or she will get underneath the vehicle to find the exact location of the sensor. While under the vehicle, the mechanic will examine both the sensor itself and the corresponding wires for any superficial damage to the unit. The mechanic will then remove the old speed sensor and install the new one.

If the mechanic believes that a fuse or bad wire has caused the speedometer to stop working, he or she will begin by examining the fuse to check if it has been blown. If so, the mechanic will replace the fuse. The mechanic will also examine the wires running from the speedometer to the speed sensor to see if they have been damaged in any way.

In the case of a problem with the ECU, the mechanic will typically replace the entire ECU. Because resetting the unit may just be a temporary fix, replacing the ECU is the only way to ensure that it works properly. When the mechanic installs the new ECU, he or she will turn the ignition key to the “Auxiliary” position. This will allow the new ECU to turn on and begin the process of managing vehicle systems. When the vehicle is turned on, it should be begin adjusting systems to run optimally.

In all repairs, a mechanic will clear any trouble codes that may have been produced by the vehicle’s ECU using a code reader/scanner. Before leaving, the mechanic will test drive the vehicle to ensure that all systems are working properly and the speedometer has resumed functionality.