OBD-II Diagnostic Trouble Code
P0579 — Cruise Control Multi-Function Input A Range/Performance
P0579 means the cruise control multi-function input A is out of the expected range or not plausible. Many systems use a resistor ladder so each button produces a specific voltage; the ECM saw a voltage that does not match any valid button state.
Severity 2/5
Truck-relevant
Service soon
Severity
Service soon
Cruise Control Multi-Function Input A Range/Performance
Code
P0579
Category
Powertrain
Subsystem
Speed
Truck-relevant
Yes
What this means for truckers
Service this week on a Cummins X15, Detroit DD15, PACCAR MX-13. Not an immediate stop, but ignoring it usually leads to a more expensive fix downstream.
Before you replace parts — try this first
P0579 on the Speed system is most often worn cruise switch with internal resistance changes — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Cruise control may not engage, may cancel unexpectedly or respond to the wrong button. Engine speed control or PTO functions using the same switches may be affected.
Common causes
- CommonWorn cruise switch with internal resistance changes ($100–$350)
- OccasionalCorroded connector or high-resistance wiring ($100–$300)
- OccasionalFaulty clock spring ($200–$600)
How to fix
Measure switch output voltage for each button and compare to spec
When to use: First step
Clean connectors and check wiring resistance
When to use: When voltages are slightly off
Replace the switch or clock spring
When to use: When values are out of spec
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0500 — Vehicle Speed Sensor Malfunction
- → P0501 — Vehicle Speed Sensor Range/Performance
- → P0502 — Vehicle Speed Sensor Low Input
- → P0503 — Vehicle Speed Sensor Intermittent/Erratic/High
- → P0506 — Idle Control System RPM Lower Than Expected
Frequently Asked Questions
Can I drive with code P0579?
P0579 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P0579 on a commercial truck?
Total repair cost ranges $100–$600 depending on the root cause. The cheapest fix is usually the first one listed below — Worn cruise switch with internal resistance changes — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0579 fail a DOT inspection?
P0579 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0579 and related codes?
P0579 is closely related to: P0500 (Vehicle Speed Sensor Malfunction), P0501 (Vehicle Speed Sensor Range/Performance), P0502 (Vehicle Speed Sensor Low Input), P0503 (Vehicle Speed Sensor Intermittent/Erratic/High). These codes share the same subsystem (speed) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0579 is set without the companions, the issue is more isolated.
How do I prevent P0579 from coming back after a repair?
For P0579 (Cruise Control Multi-Function Input A Range/Performance), prevention centers on the speed system. Inspect wheel speed sensor wiring at PM (rodents love it). Keep ABS tone rings clean.