P0585 — Cruise Control Multi-Function Input "A"/"B" Correlation

What exactly does P0585 mean?

P0585 means the powertrain control module detected an incorrect relationship between cruise-control multi-function input A and input B, such as contradictory switch states.

Can I safely drive with P0585 stored?

P0585 usually affects cruise operation rather than basic propulsion, but cruise control may be unavailable or unreliable. Avoid relying on it until the circuit has been diagnosed and repaired.

Does P0585 always require a new cruise-control switch?

No. P0585 can also result from damaged wiring, a poor connector, an incorrect pedal-switch signal, or a module input fault, so testing should precede parts replacement.

Why does P0585 appear only when cruise control is used?

The fault may remain hidden until the switch inputs are exercised or the vehicle reaches a condition where cruise engagement is permitted and the A/B mismatch becomes detectable.

P0585 indicates a mismatch between two cruise control input signals inside your vehicle's cruise control circuit. The powertrain control module continuously compares the signal coming through input "A" against the signal from input "B" — when those two readings don't correlate within the expected parameters, the module logs P0585 and illuminates the check engine light. This code lives in the powertrain group because cruise control directly affects engine management, especially on vehicles where throttle input is electronically controlled.

The cruise control system depends on multiple sensors and switches feeding data to the ECU while you drive. The module monitors this data stream constantly, watching for voltage values that fall outside the factory-defined range. When readings stay out of bounds across a set number of drive cycles — the exact number varies by manufacturer — the control unit confirms the fault and stores P0585. The freeze frame data captured alongside the code is gold for diagnosis: it records engine RPM, calculated load, coolant temperature, and vehicle speed at the exact moment the problem was detected, giving you a snapshot of what the vehicle was doing when things went sideways.

Common Symptoms of P0585

The cruise control system may stop responding entirely or work only sporadically, leaving you unable to maintain set speed on the highway. A limp-home mode can engage on some vehicles, reducing power output to protect other systems until the fault is addressed. Fuel economy sometimes climbs unexpectedly because the engine runs slightly richer or because you're compensating manually for lost cruise functionality. The check engine light stays on once the code is stored, though the vehicle typically remains driveable. In rare cases involving integrated throttle control, you might notice a slight hesitation or stumble when accelerating normally.

What Triggers P0585

Corrosion, looseness, or physical damage at the cruise control connector ranks as the most frequent culprit — moisture and road salt work their way into these plugs over time. A blown fuse feeding the cruise control circuit will obviously prevent proper operation and trigger the code. The control module driver itself can fail internally, though this is less common than wiring issues. Open circuits or shorted wiring anywhere between the sensors and the ECU will throw the signal correlation off. A weak or interrupted ground connection at the cruise control assembly creates the same problem, making the module read phantom voltages that don't match expected values.

How to Diagnose P0585

Start by connecting an OBD2 scanner, confirm P0585 is present, and record all freeze frame data — that snapshot tells you exactly what conditions triggered the code and guides your next moves. Scan for any other stored trouble codes as well; other active codes often point toward the root cause, and related DTCs frequently appear together when wiring is the problem. Check manufacturer technical service bulletins for your specific make and model, as many cruise control issues have documented factory fixes or software updates that solve the problem without any parts replacement. Next, perform a hands-on inspection of all wiring and connectors tied to the cruise control multi-function inputs, looking for chafed insulation, broken strands, corrosion buildup, or any connector that isn't fully seated. With the wiring harness unplugged at the cruise control assembly, use a multimeter to check for proper reference voltage from the ECU, verify clean ground continuity, and confirm signal wire integrity from end to end. Finally, clear the code, take the vehicle through a complete drive cycle that reproduces the freeze frame conditions — same speed, same load, same temperature — and see whether P0585 returns.

Repair Options for P0585

Addressing the cheapest and most common possibilities first makes sense before spending on major components. If the cruise control switch assembly or speed sensor is defective, replacement typically runs $150–$500 depending on your vehicle and what exactly needs swapping. Wiring and connector repairs — cleaning corroded pins, soldering broken wires, replacing damaged connectors — usually fall between $80 and $250. When the control module itself is at fault, repair or replacement can cost $300–$1,000, making accurate diagnosis especially important in this scenario.

Total Cost to Fix P0585

Depending on what component is actually faulty, your total bill varies considerably. Replacing a failed sensor or actuator runs $150–$500 parts and labor. Repairing wiring or connectors costs $80–$250. Control module diagnosis and repair or replacement runs $300–$1,000. In most cases, fixing P0585 lands somewhere between $80 and $1,000 total. Spending time on accurate diagnosis before buying parts always saves money — the most expensive repair is rarely where you should start.

Can You Drive with P0585?

For most drivers, the vehicle stays operational even with P0585 stored, though the cruise control won't function and you may notice slightly reduced performance or higher fuel consumption. Treat the situation as urgent if the car develops stalling, fails to start, or triggers brake or steering-related warnings — those symptoms suggest the problem has spread beyond the cruise circuit.

Related OBD2 Codes

• P0500: Vehicle Speed Sensor "A" Malfunction
• P0501: Vehicle Speed Sensor "A" Range/Performance
• P0502: Vehicle Speed Sensor "A" Low Input
• P0503: Vehicle Speed Sensor "A" Intermittent/Erratic/High
• P0504: Brake Switch "A"/"B" Correlation
• P0505: Idle Control System Malfunction