Diagnostic article Generic OBD-II
P2C18: The exhaust B-channel low fault requires an on-state electrical check
Understand the supply and command qualifications behind P2C18 before using the code to choose a component.
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.
P2C18 concerns the exhaust profile-position sensor B circuit’s low electrical classification. GM describes a driver voltage result consistent with a short toward ground while the output is on. The code does not directly describe a low physical position or a profile pin that failed to extend.
Keep circuit type and channel identity together
The classification corresponds to impedance below 0.5 Ω toward controller ground through the module’s own voltage limits. P2C16 represents the open condition for this channel, while P2C19 evaluates the high condition under an off command. Those distinctions matter when a scan report contains several profile-related faults.
The generic description’s camshaft B designation identifies the exhaust system in this table. Sensor B is a separate channel label; neither is a verified physical-cylinder assignment.
Confirm an eligible repeated observation
Supply must exceed 11 V, ignition be in crank or run and the diagnostic and on command be active. Four failed samples out of five establish the result. The one-trip reporting class does not mean that any single low reading proves a completed fault.
Preserve command, supply and electrical status before interpreting a lack of movement mechanically. The published impedance is not a connector test instruction. The source cannot identify where the ground path is located or select a sensor, harness or controller for replacement; the correct circuit procedure must establish that.
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 913. 25OBDG03B, PDF page 915. 25OBDG03B, PDF page 916.
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 Position Sensor B Circuit Low 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