Code B124, Vehicle Speed Sensor (VSS) Circuit Problem: Notes

The vehicle speed sensor uses a Permanent Magnet (PM) generator to generate an electrical signal representative of vehicle speed. This signal is brought to the BCM by circuit No. 400 (VSS high) and circuit No. 401 (VSS low), where the BCM buffers and amplifies the signal for its prospective uses. Output of the generator can be seen by using a digital voltmeter on the AC scale while rotating the generator drive (rotate front wheels).

Code B124 will set under the following conditions:

Ignition on.
No Codes EO29, EO31 or B334.
Transaxle in 4th gear (EI82 "LOW"),
No input to the BCM from the VSS.
Engine speed greater than 800 RPM.

During the time the failure is present, the continuous compressor at idle will be disabled, however, vehicle speed reading BD60 will display actual sensor reading.

NOTE: Test numbers refer to numbers on diagnostic chart.

Since the BCM amplifies and buffers the speed signal before it is sent to the ECM, Code EO24 in the ECM will set along with Code B124 in the BCM if the PM generator or circuits No. 400 and 401 have a problem. If Code B124 ever sets without setting a Code EO24, there is an internal problem in the BCM.
BCM data value BD60 displays MPH.
With the wheels turning, a voltage reading indicates that the PM generator and wiring are okay.
Checks for open in VSS circuit wiring.
Checks for ground in VSS circuit wiring prior to replacing sensor.