P06B4: Sensor supply B low may originate from a protective switch report

P06B4 is generically described as sensor power supply B low. The GM TCM row uses a different kind of evidence: the VSS2 supply switch reports excessive current or excessive switch temperature. Reading the actual monitor prevents treating the label as a complete voltage test.

Two protection conditions share the code

The current branch evaluates VSS2 supply current above 220 milliamperes. The alternative branch is a true overtemperature status from the VSS2 switch. The confirmation interval is at least 60 milliseconds, with continuous evaluation when eligible.

Main battery voltage must be above 8.75 and below 18 volts, outside cranking and the STOP key state. P0882 and P0883 disable the check. The summary does not publish a numeric temperature limit for the overtemperature flag.

Identify the protection reason

Preserve whether the fault detail indicates current or switch-temperature protection. A measured low rail voltage alone cannot identify which of these branches reported the problem. Likewise, the code does not prove that a particular speed sensor caused the excessive load.

The supply distribution and switch diagnostics need the installed transmission’s service information. Do not infer a connector or bypass the protective switch from this row. Its useful distinction is that P06B4 can carry protection-state evidence, so diagnosis should retain that status instead of reducing the entire fault to a generic low-voltage reading.

Source and applicability

This explanation covers the cited GM monitor, not every vehicle carrying this code. The application-matrix filename does not resolve cleanly to this file, so no model or engine fitment is assigned. GM diagnostic table, PDF page 935.