P0591 — Cruise Control Multi-Function Input "B" Circuit Range/Performance

P0591 — Cruise Control Multi-Function Input "B" Circuit Range/Performance. A fault in the sensor and actuator circuits. The car is usually drivable while you plan the repair. Typical causes: open or shorted wiring in the circuit, control module driver fault, faulty sensor or actuator of the affected circuit.

powertrain (engine/transmission)

Is it safe to drive?

Cruise-control function impaired P0591 usually affects speed-control operation rather than basic engine drivability. The vehicle can generally be driven without cruise, but the driver should not rely on the system. If cruise does not cancel when the brake is applied or the cancel command is selected, avoid highway use until the fault is repaired.

Typical symptoms

The check-engine light or a manufacturer warning message displays with P0591 stored in the controller.
The cruise-control set, cancel, or resume buttons do not operate reliably.
The cruise-control indicator may flash, remain on, or fail to illuminate when cruise is selected.
Cruise may engage intermittently, release immediately, or fail to resume after braking.
Other steering-wheel multifunctions may behave erratically when the switch, connector, or clock spring is at fault.
The vehicle may otherwise accelerate and stop normally because P0591 primarily affects the cruise-control function.

Common causes

Worn or contaminated cruise-control buttons within the steering-wheel multifunction switch can produce an out-of-range Input B signal.
Corroded, loose, or damaged switch connectors can create excessive resistance in the cruise-control Input B circuit.
An open, shorted, or pinched wire in the Input B path can cause P0591 to be recorded.
A poor module ground, low supply voltage, or unstable reference voltage can shift the Input B reading outside its expected range.
An incorrectly wired, incompatible, or damaged aftermarket steering wheel and cruise switch can corrupt the Input B signal.
On vehicles using a steering-wheel clock spring, intermittent contact in the clock spring or wiring harness may affect the cruise-control input.
A failed cruise-control module or ECU input stage may set P0591 after the switch, connectors, and wiring have been verified.

How to diagnose with an OBD scanner

Confirm P0591 with an OBD scanner Connect an OBD scanner, ELM327, or AIScanAuto and read stored, pending, and freeze-frame data. Confirm that P0591 is present and note whether it appeared during switch operation or a wiring disturbance. If supported, monitor the cruise-switch or Input B live-data value while pressing the set, cancel, and resume commands.
Identify the actual Input B circuit Use the vehicle wiring diagram to locate the cruise-control multifunction switch, Input B wire, connector pins, controller input, ground, and reference circuits. Do not assume a universal wire color or voltage because the pin assignment and signal range are model-specific.
Test the switch and connectors Inspect the cruise-control buttons for sticking, contamination, damaged contacts, or inconsistent clicks. Disconnect the switch and connector, then check for corrosion, bent pins, heat damage, and water intrusion. Clean or replace defective contacts before condemning the module.
Measure the Input B signal With the circuit fully connected, use a multimeter or oscilloscope to measure Input B while operating each cruise-control command. Back-probe the specified connector or controller pin and compare the voltage, waveform, and resistance with the service-manual limits. Also check for an open circuit, short to battery voltage, short to ground, and excessive harness resistance.
Check shared steering-wheel circuits If wiring and switch tests are normal but P0591 remains intermittent, inspect the clock spring, contact carrier, and related connectors on designs that use them. Correlation with other steering-wheel, speed-control, or airbag trouble codes can indicate a shared harness or clock-spring fault.
Repair and validate the cruise function Replace the failed switch, repair the wiring or grounds, or service the control module as testing indicates. Clear P0591 with the scanner, confirm the cruise input changes as commanded, and perform a final road test in a safe area before returning the vehicle to normal use.

Approximate repair cost

Independent-shop estimates for diagnosing and repairing P0591 are commonly around USD $125 to $650, depending on whether the fault is a switch, connector, harness, clock spring, or control-module input. These figures are estimates only and vary by region, labor rates, vehicle access, and parts availability.

Common questions

What does P0591 specifically identify?

P0591 identifies a range or performance problem with the cruise-control multifunction Input B circuit, usually involving the steering-wheel cruise switch, its wiring, or the controller receiving that signal.

Can the vehicle be driven with P0591 stored?

Usually yes, because the code primarily affects cruise operation. Do not use cruise until repaired, and stop using the vehicle promptly if braking, throttle override, or the cancel control fails to release cruise.

Does P0591 indicate an engine or transmission failure?

No direct engine or transmission failure is implied by P0591. The stored code points to the cruise-control input circuit, although a poor power or ground supply can affect related vehicle systems.

How can an OBD scanner help diagnose P0591?

An OBD scanner can confirm P0591, preserve freeze-frame conditions, and sometimes show live cruise-switch or Input B data. Comparing that data with the manufacturer's specifications helps distinguish a failed switch from wiring or controller problems.

When your check engine light comes on and a scan tool reveals code P0591, it points to a specific problem with the cruise control system's multi-function input "B" circuit. This isn't a vague sensor failure — the powertrain control module has detected that the electrical signal from this input falls outside its expected operating range while remaining technically valid. In plain terms, the wiring and connectors typically check out fine; what the module is flagging is a component whose output has drifted, degraded, or no longer reflects what the engine control system believes should be happening under current driving conditions.

The cruise control multi-function input "B" is a circuit that feeds data to the vehicle's computer — usually from a combination switch assembly or dedicated speed sensor input. When you set cruise control or adjust its target speed, the module compares live readings from this circuit against factory-calibrated thresholds. If those readings don't match what the module expects given your current RPM, load, and vehicle speed, it flags the discrepancy as a range or performance fault. To rule out temporary glitches, the control module runs this check multiple times across several drive cycles before actually setting P0591. When it does set the code, the module also saves a freeze frame — a snapshot of engine temperature, RPM, load, and vehicle speed at the exact moment the fault was detected. That snapshot is your most valuable diagnostic clue.

Typical Symptoms

Cruise control fails to engage, disengages unexpectedly, or operates inconsistently
Illuminated check engine light
Possible activation of reduced-power or limp-home mode depending on which module flags the fault
Slightly elevated fuel consumption if the cruise system stays partially disabled
In rare cases, related systems like traction control or stability management may show degraded performance

Common Causes

Degraded, contaminated, or drifting multi-function input "B" sensor or switch assembly
Corroded, loose, or physically damaged electrical connector at the cruise control circuit
Wiring issue — an open circuit, short to ground, or short to voltage in the signal or reference wires
Incorrect module calibration following a software update, battery disconnect, or aftermarket installation
Mechanical fault upstream — such as a binding throttle or actuator that the sensor correctly reports but the module cannot reconcile
Faulty control module output driver for the affected circuit
Blown fuse feeding the cruise control system or its associated sensors

Diagnostic Steps

Connect an OBD2 scan tool, confirm P0591 is present, and record the freeze frame data before clearing anything — that snapshot tells you exactly what engine conditions coincided with the failure.
Pull all stored codes, not just P0591. Related or surrounding codes often point to the root cause, such as a failing vehicle speed sensor that feeds the same circuit.
Check for any manufacturer technical service bulletins or software updates tied to P0591 for your specific make, model, and model year — some vehicles have known calibration flaws that a reflash can resolve.
Perform a thorough visual inspection of the wiring harness and connectors related to the cruise control multi-function input "B." Look for chafed insulation, broken strands inside wire looms, green corrosion on terminals, or pins that are pushed back instead of fully seated.
With the connector unplugged, measure reference voltage, ground integrity, and signal line continuity at the component harness using a multimeter. Compare results against published specifications for your vehicle.
If the wiring checks out, compare the live data stream for the multi-function input "B" against a known-good correlated signal — such as the vehicle speed sensor output — under the same conditions recorded in the freeze frame.
Reconnect everything, clear P0591, and complete a drive cycle that reproduces the freeze frame conditions (same speed range, engine load, and temperature). Verify the code does not return.

Repair Options and Costs

Wiring repair or connector replacement: $80–$250
Control module diagnosis and repair or replacement: $300–$1,000
Replacement of faulty cruise control sensor, switch assembly, or actuator: $150–$500

Total repair costs for P0591 typically fall between $80 and $1,000 depending on which component is ultimately at fault. The majority of cases are resolved by addressing wiring or connector issues — the least expensive route. Control module replacement, while possible, is relatively rare and should only be pursued after wiring and sensor faults are definitively ruled out.

Can You Drive With P0591?

For most drivers, the vehicle remains operational with P0591 stored. The cruise control function may be disabled or behave erratically, but core drivability is usually unaffected. That said, if the fault is tied to a module that also controls throttle response or safety systems, you may notice reduced power orlimp mode activation. Treat any accompanying stalling, hesitation, brake warning lights, or steering anomalies as urgent — stop driving and have the vehicle diagnosed promptly in those cases.