Diagnostic article Generic OBD-II
P0579: Jeep diesel cruise-switch plausibility versus voltage faults
The 2002 WG 2.7L diesel manual gives P0579 three diagnostic descriptions: cruise-switch signal plausibility, voltage too high and voltage too low.
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Documented application
DaimlerChrysler 2002 WG body with 2.7L diesel engine, ECM diagnostic procedures; subtypes retained rather than generalized to other vehicles.
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.
The 2002 WG 2.7L diesel manual gives P0579 three diagnostic descriptions: cruise-switch signal plausibility, voltage too high and voltage too low. Reading only the generic multifunction-input range/performance title loses this useful distinction. The complaint must be matched to the subtype reported by the ECM.
Plausibility is not the same as a short circuit
The plausibility procedure examines excessive resistance in the switch-signal and switch-ground paths before reaching the switches or ECM. A signal can be electrically present yet fail to represent a valid switch request. That calls for a different investigation from a line held continuously at an electrical extreme.
The high-voltage branch considers an open signal, an open ground and a short to voltage, including the ON/OFF/SET switch path. The low-voltage branch distinguishes the ON/OFF/SET switch from the RESUME/ACCEL switch and checks shorts to chassis ground and sensor ground. Isolating one switch and observing recovery identifies a different fault section from an input that remains wrong with both switches excluded.
A complete verification checks every command
The original procedure assesses all cruise-switch buttons, which matters because one functioning button does not validate the whole assembly. Any required operational verification belongs to a qualified workshop under appropriate conditions; this overview provides no road-test instructions.
Preserve the subtype, note whether the failure affects one command or several, and verify the repaired signal path after correction. The circuit arrangement and diagnostic divisions here are specific to the cited 2002 WG diesel system.
Source: DaimlerChrysler factory diagnostic procedure, physical PDF pages 131–136. Original archive member: WG/02wged.pdf in the factory-manual download.
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
Cruise Control Multi-Function Input A Circuit Range/Performance
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