What Does P0620 Mean?
The PCM/ECM has detected a malfunction in the Vehicle Speed Sensor (VSS) output 'B' circuit. This is the speed signal output from the control module to other modules or systems that need vehicle speed data (such as the ABS module, transmission, or instrument cluster). The driver may notice an inoperative speedometer, erratic transmission shifting, or disabled cruise control.
Common Causes
30%
Damaged wiring or connector in the VSS output B circuit
25%
Faulty vehicle speed sensor providing no or incorrect signal
20%
PCM/ECM internal failure on VSS output driver
15%
Receiving module (instrument cluster, TCM) not properly receiving the signal
10%
Ground circuit issue affecting the VSS output signal quality
Diagnostic Steps
1
Monitor the vehicle speed PID on the scan tool while driving. Compare the displayed speed to actual GPS speed or a known-accurate speedometer. Look for dropouts, erratic readings, or zero readings.
2
Inspect the VSS output B circuit wiring from the PCM to the receiving module. Check for chafed wires, corrosion, or damaged connectors at both ends.
3
Using an oscilloscope, capture the VSS output signal at the PCM connector while driving. The signal should be a clean square wave that increases in frequency proportional to vehicle speed.
4
Check for proper ground connections at the PCM and receiving module. Measure ground circuit resistance — should be less than 0.5 ohms.
5
If wiring is intact and the VSS input to the PCM is correct but the output is faulty, the PCM output driver may be damaged and the PCM may need replacement.
Estimated Repair Cost
$80 - $600
Parts + labor, varies by vehicle and location
The PCM/ECM has detected a malfunction in the Vehicle Speed Sensor (VSS) output 'B' circuit. This is the speed signal output from the control module to other modules or systems that need vehicle speed data (such as the ABS module, transmission, or instrument cluster). The driver may notice an inoper...
The most common cause of P0620 (Control Module VSS Output "B" Malfunction) is: Damaged wiring or connector in the VSS output B circuit
Typical repair costs for P0620 range from $80 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If the speedometer is inoperative, the driver cannot accurately judge speed, which is a safety and legal concern. Transmission shift quality may be affected. Cruise control will likely be disabled. Drive carefully using GPS for speed reference and have the issue diagnosed promptly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0620 to identify the root cause.
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Quick Info
Category
Powertrain
System
Vehicle Speed / Instrument System
Difficulty
Type
Generic (SAE)
Recommended Tools
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