P0581 – Cruise control system, multi -function switch input A circuit high

By Reinier (Contact Me)
Last Updated 2017-02-13
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0581 Mean?
2. What are the common causes of code P0581 ?
3. What are the symptoms of code P0581 ?
4. How do you troubleshoot code P0581 ?
5. Codes Related to P0581
6. Get Help with P0581

What Does Code P0581 Mean?

SPECIAL NOTES: Since code P0581 involves the cruise control system, non-professional mechanics are strongly urged to read the section in the manual for the application being worked on that describes the cruise control system very carefully, before attempting a diagnosis/repair of this code.

Failure to gain at least a basic understanding of the cruise control system on the affected application will almost certainly result in misdiagnoses, damage to the application’s electrical system, the deployment of the airbag(s) in the steering wheel, and the unnecessary replacement of parts and components.

Non-professional mechanics should also note that due to significant design differences between the cruise controls systems fitted to different applications, this guide cannot provide detailed diagnostic and repair information that will be valid for all applications under all conditions. However, the generic information provided here should enable most non-professional mechanics to diagnose and repair the most common causes of code P0581 on most applications.

Also, be aware that diagnosing some causes of this code may require the use of professional grade diagnostic equipment, or the use of special tools/equipment that may only be available to dealers. In these cases, non-professional mechanics are strongly urged to refer the vehicle to a dealer or other competent repair shop for professional diagnosis and repair.

Always bear in mind that cruise control is a safety critical system and half-baked or sloppy diagnostic/repair procedures can render the system dangerous. Cruise control systems essentially assume control of a vehicle’s speed, and many fatal crashes have occurred as the direct result of sloppy repairs to cruise control systems that prevented a driver from deactivating the system.

Therefore, non-professional mechanics that are not comfortable with working on a safety-critical system are strongly urged to refer the vehicle for professional diagnosis and repair. END OF SPECIAL NOTES.   

OBD II fault code P0581 is a generic code that is most commonly defined as  “Cruise control system, multi -function switch input “A” circuit high”, and is set when the PCM (Powertrain Control Module) detects an abnormally high input voltage from the cruise control multifunction switch. Take note that in the context of this definition, “input voltage” refers to high input voltages between the PCM and the cruise control multifunction switch, which voltages derive from several sensors and subsystems when the cruise control system is activated, such as the-

• Vehicle speed sensor
• Transmission range (gear position) sensor
• Throttle position sensor
• Cruise control activation switch
• Clutch pedal mounted cruise control deactivation switch on applications with manual transmissions
• Brake pedal -, or master cylinder mounted cruise control deactivation switch on applications with automatic transmissions. Note that on some applications, the cruise control deactivation switch is incorporated into the brake light switch.
• Brake light switch. Note that on some applications, the cruise control deactivation switch is hard-wired into the brake light switch/circuit, even though the two switches are not always integrated.

Typically, steering wheel mounted cruise control multifunction switches include controls for all the functions required to control the cruise control system. These controls include buttons/switches to-

• Activate the cruise control system
• Set and maintain the vehicles’ speed between the minimum allowable, and the maximum rated speed
• Increase the vehicles’ speed
• Decrease the vehicles’ speed
• Deactivate the cruise control system
• Cancel the cruise control system

From the above it should be obvious that the effective/correct operation of the cruise control system on any application requires that the correct signal and return voltages in ALL of the dozens of circuits that pass through the multifunction switch fall within the manufacturers’ specified values when they reach the PCM.

However, while the various input voltages may reach the multifunction switch OK, these same voltages need to passed along the PCM, which is accomplished by passing currents through a device known as a “clock spring”, which has largely replaced the sliding type of contact system used previously. Clock springs fit over the steering column behind the steering wheel, and typically consists of a compressible, or flexible conductor that either stretches, or compresses as the steering wheel is turned from side to side.

The advantage of this involves the fact that electrical connections between the cruise control multifunction switch (and other steering wheel mounted controls) remain fixed to the flexible conductor, and continuity therefore does not depend on the quality of the contact between sliding surfaces. Nevertheless, while the idea behind clock springs is sound, the execution of the idea is often less so, and many, if not most causes of code P0581 can be directly attributed to failures of, or malfunctions in the clock spring mechanism that can in turn, cause high input voltages to reach the PCM.

When such faults, failures, or malfunctions occur in the clock spring mechanism (or anywhere else in the cruise control system), the PCM will store code P0581, but depending on the application, it may or may not illuminate a warning light. Note also that on some applications as many as three fault cycles are required before a warning light is triggered.

The image below shows a typical cruise control multifunction switch removed from a steering wheel. Note that although it was not necessary to remove the steering wheel from the steering column in this case, and that the multifunction switch assembly could be removed by loosening only one screw, this is not always possible. In some cases, removing the steering wheel is the only way to remove and replace the cruise control multifunction switch.

What are the common causes of code P0581 ?

Common causes of P0581 could include the following-

• Damaged, burnt, shorted, or corroded wiring and/or connectors in any part of the cruise control system
• Defective clock spring mechanism
• Defective cruise control switches/controls that cause short circuits either to ground or battery voltage
• Defective cruise control deactivation switches that cause short circuits either to ground or battery voltage
• Bad electrical connections in any part of the cruise control system that cause a high resistance
• Failed or failing PCM. Note that this is a rare event, and the fault must be sought elsewhere before any controller is replaced

What are the symptoms of code P0581 ?

Common symptoms of code P0581 could include the following-

• Stored trouble code, and possibly an illuminated warning light
• Cruise control system may not engage
• Cruise control system may not deactivate
• Cruise control system may not activate (or deactivate) every time depending on the application, and the exact nature of the problem

How do you troubleshoot code P0581 ?

WARNING: Removing the steering wheel or performing diagnostic tests on steering wheel mounted controls can activate the airbag(s) in the steering wheel. To prevent this from happening, the procedure(s) provided in the manual for the application should be followed EXACTLY to deactivate the airbag(s) in the steering wheel before any work is performed on any control switch/button that is located on the steering wheel.   

NOTE: On many Ford applications, this code can be set by a failure of, or malfunction in the Shift Interlock mechanism because a failed mechanism may let the PCM “think” that the transmission is in “D” when it is not, or vice versa. Although this fault does not necessarily involve high input voltages reaching the PCM, this fault is not always indicated by a code, and often, the only indication that the shift interlock is defective is the fact that the vehicle can be started when the shift selector is in positions other than “D”, or “N”.

Step 1

Record all fault codes present, as well as all available freeze frame data. This information can be of use should an intermittent fault be diagnosed later on.

NOTE: Pay particular attention to any other codes (both pending and active) that may be present along with P0581, as well as the order in which additional codes were stored. In some cases, additional codes may have contributed to P0581 being set, meaning that resolving these codes may resolve P0581 as well. However, do not assume that additional codes are (or are not) related to P0581; the safety aspects of having a fully functional cruise control system demand that all additional codes be investigated properly, so ALWAYS refer to the manual for detailed information on the possible relationship between P0581 and any other codes that may be present along with P0581, or ANY other cruise control related code(s).

Step 2

Consult the manual to locate and identify all cruise control related parts, components, and switches. Also, use this opportunity to determine the location, routing, function, and color-coding of all associated wiring.

Step 3

Once all parts, components, and wiring are positively located and identified, perform a thorough visual inspection of all relevant wiring and connectors. Look for damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors. Make repairs as required if any visible damage to wiring and/or connectors is found.

Clear all codes after repairs are complete, and operate the vehicle for at least one drive cycle (be sure to include activating the cruise control system) to see if the code returns.

NOTE: Bear in mind that wiring issues is a common cause of this code, so take as much time and trouble as it takes to open harnesses, or to remove trim panels and/or carpets to gain full access to all relevant wiring. An extra hour or two spent on this step can save many hours, or even days, on looking for the fault elsewhere if this inspection is not carried out properly.  

Step 4

If no visible damage to wiring is found, resist the temptation to look for complex causes. Consult the manual on the possible causes that are the most likely to cause P0581 on the affected application, and work through these possibilities one by one.

For instance, on many applications, various parts of the cruise control system are protected by several fuses that may, or may not be located in the same fuse box. One blown fuse can prevent the system from working, so identify all implicated fuses, and use a dedicated circuit tester to test the circuits involved. However, bear in mind that fuses do not always need a reason to blow, so if the circuits that are protected by all implicated fuses check out but blown fuses are found, simply replace the fuse.

WARNING:  Replace blown fuses ONLY with fuses that are rated for that particular circuit by the manufacturer, and do NOT continue to replace fuses that blow immediately, or soon after being inserted, since this indicates a serious electrical issue that could be located almost anywhere in the affected circuit. If any fuse blows repeatedly, use the wiring diagram in the manual to isolate the affected circuit, and make repairs ONLY as directed in the manual to ensure that the short circuit is repaired reliably. Note that since short circuits can be either to ground, or to battery positive, following the testing procedures prescribed in the manual is highly recommended to prevent damage to the vehicles’ electrical system.

The image below shows a typical circuit tester that could save hours of diagnostic time, provided it is used as directed in the manual. Do NOT use a simple test light during this step, since test lights cannot measure resistance.

Step 5

If the code persists but all fuses and/or circuits check out, prepare to test the cruise control deactivation switch (es). However, be sure to follow the manufacturer’s recommended test methods EXACTLY to avoid obtaining misleading, or inaccurate results. Compare all obtained readings with the values stated in the manual, and replace all switches that do not conform to the manufacturer’s specifications, even if the deviation in resistance or continuity is only marginal.

Deactivation switch failures are perhaps the second-most common cause of code P0581, so if a defective deactivation switch is found, resist the temptation to replace it with a cheap, aftermarket part. Aftermarket parts seldom (if ever) offer the same performance, reliability, and durability as OEM parts do.

Clear all codes after repairs are complete, and operate the vehicle for at least one drive cycle (be sure to include activating the cruise control system) to see if the code returns.

Step 6

While the steps up to, and including Step 5 will resolve code P0581 in nine cases out of every ten, the tenth instance might require removing either the multifunction switch from the steering wheel, or removing the steering wheel to gain access to the terminals on the multifunction switch for the purposes of testing resistance, continuity, ground, and reference voltages in circuits between the switch and the PCM.

While it is possible for non-professional mechanics to perform these tasks successfully, it is NOT recommended, due to the distinct possibility that damage to the vehicles’ electrical system could occur, or worse, that personal injuries could occur if and when the steering wheel airbags are deployed inadvertently.

Therefore, the wiser option at this point would be to refer the vehicle for professional diagnosis and repair, but non-professional mechanics who opt to continue the diagnostic/repair procedure themselves should ONLY do so by strictly following the directions provided in the manual, and then only if they are FULLY confident in their ability to complete the process successfully.

Codes Related to P0581

• P0578 – Relates to “Cruise Control Multi-Function Input “A” Circuit Stuck”
• P0579 – Relates to “Cruise Control Multi-Function Input “A” Circuit Range/Performance”

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