Diagnostic article Generic OBD-II
P06A4: transmission speed-sensor supply 1 undervoltage
P06A4 monitors speed-sensor supply VSS1 in the transmission-controller table.
Read before applying this article
Documented application
2025 GM 25OBDG07A Part2 diagnostic monitor documentation; the application-matrix filename mismatch is unresolved, so no model or engine applicability is inferred.
The code alone does not identify a failed part or establish that a vehicle is safe to drive. Confirm the vehicle, reporting module and applicable service procedure.
P06A4 monitors speed-sensor supply VSS1 in the transmission-controller table. This implementation is especially important because the catalog’s reference-voltage D wording does not mean the monitored rail is necessarily a five-volt sensor supply.
The documented threshold is eight volts
The table fails VSS1 below 8,000 millivolts, with 250 millivolts of hysteresis and at least 75 milliseconds of confirmation. Battery voltage must be above 8.75 and below 18 volts. Cranking and Stop key status are excluded, and P0882 or P0883 disables the check.
These conditions distinguish an inadequate regulated sensor supply from an observation made during an excluded vehicle-power state. They also show why applying a generic five-volt-reference test would be inappropriate here.
What to confirm
Establish which speed-sensor supply the vehicle’s controller identifies as VSS1 and retain its voltage together with battery and power-state information. The code does not directly state that the shaft speed itself is low; it concerns the electrical supply used by the sensor network.
Verification should show the VSS1 low-supply diagnostic completing after its battery and state prerequisites are met. A normal speed value seen later is narrower evidence than a demonstrated stable supply and monitor pass. The table does not name a particular sensor as the cause of the rail undervoltage.
Documentation and applicability
These details describe the monitor in GM’s 2025 25OBDG07A Part2 file. Its application-matrix filename does not match the download index, so model and engine applicability remain unresolved. Use the vehicle’s correct service information before applying these calibration details.
Article source documents
Source checks describe how the text was prepared; they do not certify a diagnosis or confirm compatibility with every vehicle using this code.
Original code reference
Dictionary definition
Sensor Reference Voltage D Circuit Low
This definition retains its original catalog scope. The article above is limited to its explicitly documented application.
Reference scope
Generic OBD-II definition.
A manufacturer label does not establish the model, year, engine or module to which a diagnosis applies. Read the safety and diagnostic limits.
Definition source
- DTC Database: pinned community code definitions
Source checked · MIT