Diagnostic article Generic OBD-II
P2078: A high tuning-position code has an impossible printed voltage condition
Understand the supported scope of GM P2078 and why its contradictory voltage inequalities must not become a guessed test procedure.
Read before applying this article
Documented application
2025 GM 07A-1 documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file.
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.
P2078 is the high-circuit entry for intake manifold tuning-valve position on bank 1. The GM strategy names a maximum-range assessment of the raw position voltage. However, its printed malfunction condition cannot be used literally as a valid numerical test.
The source does not provide a consistent high threshold
The original row requires the same raw voltage to be below 4.8 V and above 6.55 V at once. Visual inspection confirms both inequalities and the joining word. This article does not reverse a sign, substitute an OR relationship or borrow a threshold from a different sensor to hide that contradiction.
The surrounding conditions remain useful: battery voltage is above 9 V and below 17.5 V, the evaluation interval is 0.05 second and reporting is two-trip. The feedback configuration must also match the controller's listed enable conditions.
Retain evidence without asserting the wrong failure boundary
Record raw position data, signal format, supply and the exact diagnostic status. A decoded valve angle is not interchangeable with the raw electrical quantity. The code's high-range name also does not demonstrate that the mechanism is stuck open or that the manifold needs replacement.
The matching controller calibration or service procedure must establish the intended high boundary before a reproduction test is interpreted. Until that issue is resolved, the source supports identifying the monitored signal and its operating context, but not a complete numerical diagnosis or a specific repair.
Source and applicability
2025 GM 07A-1 documented monitor only. Vehicle, engine and controller calibration applicability must be established separately; no model fitment is inferred from the file. GM PDF, physical page 931.
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
Intake Manifold Tuning (IMT) Valve Position Sensor/Switch Circuit High 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