What Does P0578 Mean?
The ECM has detected that the cruise control multi-function input 'A' circuit is stuck, meaning the voltage on the input is not changing when buttons are pressed or is fixed at a single button-press voltage level. This indicates a mechanically stuck button, a short circuit that mimics a constant button press, or a frozen signal that does not respond to driver input.
Common Causes
40%
Physically stuck cruise control button in the stalk or steering wheel module due to debris, spill residue, or mechanical failure
25%
Shorted wiring in the cruise control circuit holding the signal at a specific voltage level that corresponds to a button press
20%
Failed resistor in the cruise control resistive-ladder switch network creating a permanent resistance value on the circuit
15%
Corroded connector causing a fixed resistance path that the ECM interprets as a constant button press
Diagnostic Steps
1
Step 1: Monitor the cruise control input 'A' voltage on live data with the engine running. Note the resting voltage. Press and release each cruise button and verify the voltage changes and returns to the rest state. A fixed voltage confirms a stuck condition.
2
Step 2: Physically inspect each cruise control button for free movement. Press and release each button, feeling for a proper click and return spring action. Check for sticky residue or debris around button edges.
3
Step 3: Disconnect the cruise control switch connector. If the ECM input voltage returns to the rest state, the fault is in the switch assembly. If it remains stuck, the wiring has a short.
4
Step 4: With the switch disconnected, measure resistance across the switch terminals. Each button position should produce a distinct resistance, and the rest position should show either open circuit or a specific high resistance. A constant reading regardless of button position confirms a failed switch.
5
Step 5: If the wiring is shorted, trace the harness from the switch connector to the ECM, looking for pinched wires, chafing, or shorts. Repair the wiring and verify all button positions produce correct voltage levels.
Estimated Repair Cost
$40 - $350
Parts + labor, varies by vehicle and location
The ECM has detected that the cruise control multi-function input 'A' circuit is stuck, meaning the voltage on the input is not changing when buttons are pressed or is fixed at a single button-press voltage level. This indicates a mechanically stuck button, a short circuit that mimics a constant but...
The most common cause of P0578 (Cruise Control Multi-Function Input "A" Circuit Stuck) is: Physically stuck cruise control button in the stalk or steering wheel module due to debris, spill residue, or mechanical failure
Typical repair costs for P0578 range from $40 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
A stuck cruise control input may cause cruise to engage unexpectedly, continuously accelerate, or not respond to driver input. The brake pedal always serves as a failsafe to cancel cruise control. The ECM typically disables cruise when a stuck input is detected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0578 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cruise Control System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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