P2594: A turbo-speed plausibility mismatch with a bank-label caveat

The cited P2594 monitor compares a gradient-limited turbo-speed estimate against the current speed reading. An absolute difference greater than 250,000 rpm is listed as the failure criterion. Engine speed must be above 1,000 rpm, and the row gives a 50 ms interval.

Distinguish plausibility from a speed limit

The threshold belongs to a difference between two signals. It must not be presented as the turbocharger’s permitted maximum speed. A sharp signal change can create disagreement with a rate-limited reference even when an isolated displayed value looks plausible.

For useful verification, keep both the current and reference values with the event timing. Clearing the code and seeing a stable rpm display does not show whether the same comparison has run under its enable conditions.

Which sensor is meant?

The dictionary calls this sensor B, but GM’s row calls the signal bank 1. The adjacent P2579 row uses bank 2, leaving the relationship between generic letters and source-specific bank labels unverified. Different naming conventions do not by themselves prove either source is wrong. Confirm the specific module calibration and service naming before identifying a sensor location. The supported conclusion is a plausibility disagreement, not proof of actual overspeed or a particular failed component.

Document scope and source

2025 GM 25OBDG07A Part 2 documented monitor only; its application-matrix filename join is unresolved. No model, engine or universal calibration applicability is inferred. These figures explain the cited controller logic, not a vehicle-specific repair instruction. Match the vehicle’s service information before applying them.

GM physical PDF page 884.