What Does P0591 Mean?
The cruise control multi-function input 'B' circuit is exhibiting range/performance issues, meaning the signal values from the cruise switches are outside the expected range or are not changing as expected during operation. The switches may be partially working but with degraded signal quality. The driver may experience intermittent cruise control operation or certain buttons not responding as expected.
Common Causes
35%
Worn cruise control switch contacts producing inconsistent resistance values
25%
High resistance in the clockspring circuit from wear or corrosion
20%
Intermittent wiring connection with variable resistance
12%
Failed resistor in the switch resistor ladder (shifted value)
8%
Electromagnetic interference affecting the signal circuit
Diagnostic Steps
1
Monitor the cruise control input PID while pressing each button repeatedly — look for inconsistent voltage readings, slow response, or values that don't match the expected resistor ladder voltages.
2
Measure the resistance of each switch position with a DVOM and compare to manufacturer's specifications — values that are close but out of tolerance indicate worn contacts or shifted resistors.
3
Check the clockspring circuit for added resistance by measuring end-to-end continuity while slowly rotating the steering wheel — resistance should remain constant; any fluctuation indicates a worn clockspring.
4
Inspect the cruise control switch connector and the clockspring connectors for corrosion or spread pins that could add resistance to the circuit.
5
If available, use an oscilloscope on the input signal to look for noise or signal instability that might push the signal outside the PCM's expected voltage windows.
Estimated Repair Cost
$100 - $550
Parts + labor, varies by vehicle and location
The cruise control multi-function input 'B' circuit is exhibiting range/performance issues, meaning the signal values from the cruise switches are outside the expected range or are not changing as expected during operation. The switches may be partially working but with degraded signal quality. The ...
The most common cause of P0591 (Cruise Control Multi-Function Input "B" Circuit Range/Performance) is: Worn cruise control switch contacts producing inconsistent resistance values
Typical repair costs for P0591 range from $100 to $550, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Safe to drive. Cruise control may function intermittently or erratically. If the cruise system engages unpredictably, the driver should keep a foot near the brake pedal. Normal vehicle control is not affected.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0591 to identify the root cause.
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Quick Info
Category
Powertrain
System
Cruise Control / Speed Control
Difficulty
Type
Generic (SAE)
Recommended Tools
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