What Does P0579 Mean?
The ECM has detected a range/performance issue with the cruise control multi-function input 'A' circuit. The signal voltage changes when buttons are pressed but does not match any expected valid voltage level in the ECM's lookup table. This typically means the resistive-ladder switch is producing intermediate values that fall between defined button positions, often due to component drift or contact resistance issues.
Common Causes
35%
Degraded resistors in the cruise control switch resistive-ladder network producing drift in button-position voltage levels
30%
Corroded connector adding series resistance that shifts all button-position voltages outside their acceptance windows
25%
Partially worn cruise control switch contacts creating variable contact resistance during button presses
10%
Clock spring with increased trace resistance due to wear, adding enough resistance to shift the voltage reading out of range
Diagnostic Steps
1
Step 1: Monitor the cruise control input 'A' voltage while pressing each button. Record the voltage for each position and compare to the manufacturer's voltage specification chart. Note which positions fall outside their defined ranges.
2
Step 2: Measure resistance at the cruise control switch connector for each button position. Compare to manufacturer specifications. A deviation of more than 10-15% will cause the ECM to reject the input.
3
Step 3: Clean all cruise control circuit connectors with electrical contact cleaner. Corrosion adds resistance that shifts the entire voltage ladder. Retest after cleaning.
4
Step 4: Measure the clock spring trace resistance on the cruise control circuit (disconnect both ends and measure through). Normal is less than 2-3 ohms. Higher resistance indicates a worn clock spring adding enough series resistance to shift voltage readings.
5
Step 5: If cleaning connectors does not resolve the drift, replace the cruise control switch assembly. If the clock spring resistance is high, it should also be replaced. Verify all button positions produce voltages within the ECM's acceptance window.
Estimated Repair Cost
$40 - $400
Parts + labor, varies by vehicle and location
The ECM has detected a range/performance issue with the cruise control multi-function input 'A' circuit. The signal voltage changes when buttons are pressed but does not match any expected valid voltage level in the ECM's lookup table. This typically means the resistive-ladder switch is producing in...
The most common cause of P0579 (Cruise Control Multi-Function Input "A" Circuit Range/Performance) is: Degraded resistors in the cruise control switch resistive-ladder network producing drift in button-position voltage levels
Typical repair costs for P0579 range from $40 to $400, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Cruise control buttons may be unresponsive or interpreted incorrectly by the ECM. In most cases the ECM will simply disable cruise control when it detects out-of-range inputs, making this a convenience issue rather than a safety concern.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0579 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cruise Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
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