Diagnostic article Generic OBD-II
P0652: Reference B low identifies the second TCM reference rail
P0652 in this GM table monitors VREF2 below 4.5 volts and is inhibited by the TCM’s main supply-voltage faults.
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Documented application
2025 GM 25OBDG07A Part 2, specific documented monitor only. Vehicle, engine and calibration applicability require confirmation; application-matrix filename join is unresolved.
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.
P0652 concerns sensor reference voltage B. The cited transmission controller calls the affected supply VREF2, distinguishing it from the first reference rail used by P0642. That channel identity matters when several sensors or references are present.
The second rail has its own monitored value
The documented low boundary is 4.5 volts, with 50 millivolts of hysteresis and a confirmation period of at least 40 milliseconds. The check runs continuously when the main battery supply is above 8.75 and below 18 volts, outside cranking and the STOP key state.
P0882 and P0883 disable the monitor. Their presence can therefore explain why clearing P0652 and observing no recurrence does not establish that VREF2 has passed its assessment.
Do not substitute a healthy first rail
A normal VREF1 reading does not verify VREF2. Preserve the actual B-rail measurement, its affected input context and the main supply status. The shared numerical threshold does not make the two circuits interchangeable.
The source gives rail-level evidence and a type-A classification, but no list of connected sensors or connector pins. The vehicle’s wiring information is needed to locate the low condition. It could not be assigned to a particular component from this code alone. Follow the approved diagnostic procedure and confirm the correct rail under eligible monitor conditions before treating a clear fault memory as proof of repair.
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 910.
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 B 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