P2159 means the engine or transmission control module has detected an out-of-range, erratic, or implausible signal from the secondary vehicle speed sensor (VSS B). The module compares this input against expected values and other speed references, and sets the code when the comparison fails.
The sensor itself can fail internally, producing no signal, an intermittent signal, or a signal outside the expected range. This is the single most common cause of P2159.
Open, shorted, corroded, or poorly connected wiring between the sensor and the control module can distort or interrupt the signal.
A chipped, dirty, or incorrectly spaced tone ring changes the signal pattern and can cause range/performance faults even when the sensor is good.
If the sensor is loose, misaligned, or installed with the wrong gap, the signal amplitude or timing can fall outside calibrated limits.
On vehicles that derive VSS B data from an ABS wheel-speed sensor or another module, a failing source sensor or bus communication fault can set this code.
A rare internal PCM/ECM fault can misinterpret a valid speed-sensor signal. This should only be considered after the sensor, wiring, and tone ring have been ruled out.
No. PCM failure is an uncommon cause of P2159. Most cases are resolved by replacing the faulty speed sensor, repairing wiring, or correcting a tone-ring or mounting problem.
Many vehicles use two speed inputs for redundancy or different functions. Sensor A may feed the speedometer and transmission, while sensor B may serve cruise control, traction control, or a separate control module. The exact role varies by manufacturer.
Short trips are usually possible, but an inaccurate speed signal can affect transmission shifting, cruise control, and ABS/traction systems. It is best to diagnose it promptly, especially if shifting feels abnormal.
Not necessarily. On some vehicles VSS B is sourced from an ABS wheel-speed sensor, so an ABS fault can trigger P2159, but the code can also originate from a separate transmission or driveshaft speed sensor.