What Does P0593 Mean?
The cruise control multi-function input 'B' circuit is reporting a high voltage condition. The signal voltage is above the maximum expected threshold, indicating an open circuit, disconnected switch, or a short to the voltage reference. The PCM cannot determine which cruise function the driver is requesting and will disable the cruise control system entirely.
Common Causes
35%
Open circuit in the cruise control switch or its connector (disconnected)
25%
Broken wire in the clockspring or steering column harness
20%
Short to voltage (5V reference or B+) in the signal circuit
12%
Corroded or backed-out pin in the switch or clockspring connector
8%
Worn clockspring ribbon cable with broken trace on the cruise circuit
Diagnostic Steps
1
Monitor the cruise control input 'B' PID — a reading at or near the reference voltage (5V) with no buttons pressed suggests an open circuit condition.
2
Verify the cruise control switch connector at the clockspring is fully seated — remove the steering column covers and check for a loose or disconnected plug.
3
With the switch connector accessible, use a jumper wire to short the signal pin to ground through a known-good resistor matching one of the switch values — verify the PID changes on the scan tool to confirm the wiring from the clockspring to the PCM is intact.
4
Check the clockspring by measuring continuity on the cruise circuit pins while turning the steering wheel lock to lock — an intermittent or permanent open indicates a worn clockspring ribbon.
5
Inspect all connectors in the circuit path for backed-out pins, spread female terminals, or corrosion — pay special attention to the connector under the steering column where the clockspring plugs in.
Estimated Repair Cost
$100 - $600
Parts + labor, varies by vehicle and location
The cruise control multi-function input 'B' circuit is reporting a high voltage condition. The signal voltage is above the maximum expected threshold, indicating an open circuit, disconnected switch, or a short to the voltage reference. The PCM cannot determine which cruise function the driver is re...
The most common cause of P0593 (Cruise Control Multi-Function Input "B" Circuit High) is: Open circuit in the cruise control switch or its connector (disconnected)
Typical repair costs for P0593 range from $100 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. Cruise control will not function. There is no impact on vehicle control, braking, or engine operation. If the clockspring is the root cause, the airbag warning light may also be illuminated, which would be a separate safety concern requiring prompt attention.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0593 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cruise Control / Speed Control
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
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