Diagnostic article Generic OBD-II
P2B39: An exhaust profile-actuator open result concerns the energized drive path
Understand the output-circuit evidence behind P2B39 before attributing it to an exhaust cam-profile mechanism.
Read before applying this article
Documented application
2025 GM 25OBDG03B documented monitor only. Vehicle, engine and calibration applicability must be confirmed from the matching service information; no model fitment 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.
P2B39 concerns an open electrical result in the exhaust camshaft profile-actuator circuit. GM names the documented channel exhaust actuator 2, while the generic description uses actuator B. Neither label alone establishes a physical cylinder, pin or connector location.
The monitor asks whether the powered path is intact
The controller compares measured output voltage with its own open-load thresholds while the driver is on. The listed electrical classification represents impedance above 200 kΩ toward controller ground. This is a circuit-integrity assessment, not a measurement of whether the profile pin completed a commanded stroke.
That difference matters when an actuator appears inactive. Missing movement can follow an unavailable drive circuit; it cannot independently prove a mechanical profile failure while the electrical open result remains unexplained.
Observe the qualified sample sequence
The test requires diagnostic enablement, system supply above 11 V and the ignition in crank or run. Four failures out of five samples produce the fault classification, with one-trip reporting noted separately. A single reading outside those conditions does not reproduce the monitor.
A useful record ties the on command, supply and driver status to the exact exhaust channel. The summary does not distinguish a disconnected load from an interruption elsewhere in the circuit, nor does it justify replacing the complete camshaft assembly. Hardware localization needs the applicable electrical procedure.
Source and applicability
2025 GM 25OBDG03B documented monitor only. Vehicle, engine and calibration applicability must be confirmed from the matching service information; no model fitment is inferred. These criteria explain controller logic, not a complete repair procedure. 25OBDG03B, PDF page 873. 25OBDG03B, PDF page 874. 25OBDG03B, PDF page 875.
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
B Camshaft Profile Actuator B Control Circuit/Open Bank 1
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