P0587 Cruise Control Vent Control Circuit Low

P0587 is an OBD-II diagnostic trouble code that indicates a low electrical signal in the Cruise Control Vent Control circuit.

In simple terms, the vehicle's control module has detected that the electrical signal in the circuit controlling the cruise-control vent actuator is lower than the expected value.

This code is generally related to the vacuum-operated portion of the cruise-control system on vehicles that use a vacuum vent valve or vent solenoid. The vent circuit is important because it allows the system to release or reduce vacuum when cruise control needs to disengage.

A low signal does not necessarily mean that the vent valve itself is defective. The problem could also be caused by wiring, a connector, a fuse, a short to ground, insufficient power supply, or a control-module issue.

What Does P0587 Mean?

The code can be broken down as follows:

• P – Powertrain-related diagnostic trouble code

• 05 – Cruise-control and related speed-control system

• 87 – Specific fault identifier

• Cruise Control Vent Control – The electrical circuit controlling the cruise-control vent function

• Circuit Low – The control module detects an electrical signal lower than the expected range

The key word is "Low."

This generally refers to the electrical signal or voltage in the control circuit, not necessarily low vacuum pressure.

This distinction is important because P0587 is an electrical diagnostic code even though the component being controlled may be part of a vacuum-operated cruise-control system.

What Is the Cruise Control Vent Circuit?

Older and some mechanically designed cruise-control systems use vacuum to control the throttle.

The system can contain several vacuum-related components, including:

• Vacuum actuator

• Vacuum reservoir

• Vacuum hose

• Cruise-control servo

• Vent valve or vent solenoid

• Vacuum control valves

• Brake-related vacuum release mechanism

The cruise-control system must be able to maintain vacuum when cruise control is active and release that vacuum when cruise control is cancelled or disengaged.

The vent circuit plays an important role in this process.

When the system needs to disengage cruise control, the vent valve can open and allow the vacuum-controlled actuator to release.

This provides a rapid way to remove cruise-control throttle control.

What Does "Circuit Low" Mean?

"Circuit Low" describes an electrical condition detected by the control module.

It does not simply mean that the vent valve is mechanically stuck open.

Depending on the circuit design, a low condition can occur because of:

• Short to ground

• Damaged wiring

• Incorrect voltage supply

• Faulty solenoid

• Internal coil problem

• Poor electrical connection

• Control-module driver problem

The exact expected voltage depends on the vehicle's electrical architecture.

Symptoms of P0587

The symptoms can vary considerably depending on the vehicle.

Possible symptoms include:

• Cruise control does not operate

• Cruise control disengages unexpectedly

• Cruise control cannot be activated

• Cruise-control warning light

• Check Engine Light

• Cruise control works intermittently

• Difficulty maintaining the selected speed

• Cruise control cancels when activated

• Cruise-control system becomes unavailable

In many vehicles, the engine itself may continue to run normally.

The main problem is usually associated with the cruise-control system rather than basic engine operation.

Can P0587 Cause Cruise Control to Stop Working?

Yes.

The cruise-control system may be disabled if the control module detects an electrical fault in the vent control circuit.

This is understandable from a safety perspective.

Cruise control must be capable of disengaging reliably.

If the control module cannot confirm that the vent circuit is functioning correctly, it may prevent cruise control from operating.

Common Causes of P0587

Several different faults can produce a low circuit condition.

1. Short to ground

A shorted control wire can pull the circuit voltage down.

This is one of the important causes to consider when diagnosing a "Circuit Low" DTC.

The damaged wire may be touching:

• Chassis ground

• Engine ground

• Another grounded component

2. Faulty cruise-control vent solenoid

The vent solenoid may have an internal electrical fault.

Its coil could be damaged or have resistance outside the manufacturer's specification.

3. Damaged wiring

The control wire may be:

• Cut

• Chafed

• Pinched

• Corroded

• Partially broken

A damaged wire can cause abnormal voltage at the control module.

4. Corroded connector

Corrosion can increase resistance or interfere with the electrical connection.

Water intrusion around the engine compartment is particularly important on older vehicles.

5. Loose connector terminal

A terminal may not make proper contact with the solenoid or control module.

This can produce intermittent cruise-control problems.

6. Faulty power supply

The vent control circuit may depend on a fuse, relay or switched power source.

If the power supply is incorrect, the module may detect a low circuit condition.

7. Failed fuse or relay

A blown fuse can interrupt power to the circuit.

A faulty relay can produce an unstable or missing supply voltage.

However, a blown fuse should be investigated rather than simply replaced repeatedly.

8. Internal solenoid coil problem

The solenoid coil can develop:

• Excessive resistance

• Very low resistance

• Internal shorting

• Open circuit

A coil with an internal short can draw more current than expected and contribute to a low-circuit condition.

9. Vacuum system problem

A vacuum leak itself is not necessarily the direct electrical cause of P0587.

However, if the vehicle uses an electrically controlled vacuum vent system, a mechanical problem may exist alongside the electrical fault.

The electrical circuit and vacuum system should therefore be diagnosed separately.

10. Control-module driver failure

The control module may contain an internal transistor or driver responsible for controlling the vent solenoid.

A failed driver can produce an abnormal circuit condition.

This should generally be considered only after the external circuit has been thoroughly tested.

Can a Vacuum Leak Cause P0587?

This requires an important distinction.

A purely mechanical vacuum leak normally does not directly produce a "Circuit Low" electrical fault.

For example, a cracked vacuum hose can cause the cruise control to lose vacuum, but that does not necessarily explain why the control module sees low electrical voltage.

If P0587 is stored, the electrical control circuit should be tested first.

A vehicle can potentially have both:

• An electrical vent-control problem

• A separate vacuum leak

Therefore, the two systems should not automatically be treated as the same fault.

Is P0587 Serious?

P0587 is generally not an immediate engine-damage code.

In many vehicles, the primary consequence is the loss of cruise-control functionality.

However, the cruise-control system should be considered a safety-related system because it must be capable of disengaging when requested.

If the vehicle has an electrical problem affecting the vent circuit, it is better to repair the fault rather than continue relying on the cruise-control system.

Can You Drive With P0587?

Usually, the vehicle can still be driven if:

• The engine runs normally

• The transmission operates normally

• The brakes work normally

• There are no additional serious warning lights

The main inconvenience may be that cruise control is unavailable.

Until the fault is repaired, it is advisable not to rely on cruise control.

If other systems are also malfunctioning, especially braking or throttle-control systems, the vehicle should be inspected promptly.

How to Diagnose P0587

A proper diagnosis should begin with the electrical circuit and then move toward the mechanical vacuum system if necessary.

1. Scan for all stored codes

Use a diagnostic scanner to check:

• Stored DTCs

• Pending DTCs

• History codes

• Cruise-control-related codes

• Voltage-related codes

• Communication codes

Other codes can provide valuable information.

For example, if P0587 appears together with several voltage or control-circuit codes, the problem may involve a common power supply rather than the vent solenoid itself.

2. Check whether cruise control operates

Determine whether the system:

• Does not activate at all

• Activates and immediately cancels

• Works intermittently

• Works but cannot maintain speed

• Disengages unexpectedly

The exact behavior can help narrow down the fault.

3. Inspect the vent-control solenoid

Locate the cruise-control vent valve or solenoid according to the vehicle's service information.

Check for:

• Damaged housing

• Corrosion

• Water contamination

• Loose connector

• Damaged terminals

• Broken wires

4. Check the fuse and power supply

Verify the relevant fuse.

Do not simply replace a blown fuse and consider the diagnosis complete.

If it blows again, there is likely an underlying electrical problem.

5. Check the wiring

Inspect the wiring between the control module and vent-control component.

Pay particular attention to areas where the harness can rub against:

• Engine components

• Brackets

• Body panels

• Exhaust components

• Other wiring

6. Test for a short to ground

Because P0587 identifies a low circuit condition, testing the control wire for an unintended connection to ground can be particularly useful.

The exact test procedure depends on whether the circuit is controlled on the high side or low side.

7. Test the solenoid resistance

Measure the resistance of the vent solenoid and compare it with the manufacturer's specification.

An abnormally low resistance can indicate an internal short.

An abnormally high resistance can indicate an open or damaged coil.

However, resistance testing should be performed according to the manufacturer's procedure.

8. Test the control signal

With the appropriate diagnostic equipment, verify whether the control module is commanding the vent solenoid correctly.

A technician may need to check:

• Supply voltage

• Control voltage

• Ground

• Voltage drop

• Continuity

• Current draw

9. Test the vacuum system

If the electrical circuit is functioning correctly, inspect the mechanical vacuum system.

Check:

• Vacuum hoses

• Vacuum reservoir

• Vacuum actuator

• Check valves

• Vent valve operation

A hand-held vacuum pump can be useful for testing vacuum-related components.

Testing the Cruise Control Vent Solenoid

The vent solenoid is an electrically controlled device.

Depending on the vehicle design, it may have two or more terminals.

A typical diagnostic procedure involves checking:

• Power supply

• Ground/control side

• Coil resistance

• Connector condition

• Command signal

• Current draw

The exact electrical architecture varies.

Some systems provide power to the solenoid and control the ground through the module. Other designs may use different arrangements.

Therefore, it is important not to assume that one terminal should always have battery voltage without consulting the wiring diagram.

Why Testing the Solenoid Alone Is Not Enough

Suppose the vent solenoid has the correct resistance.

That does not prove that the entire circuit is healthy.

The vehicle could still have:

• Broken control wire

• Short to ground

• Missing power supply

• Bad connector

• Poor terminal tension

• Control-module driver problem

Likewise, if the solenoid resistance is abnormal, that does not necessarily mean the wiring is good.

A complete diagnosis requires testing the component and the circuit feeding it.

P0587 and Vacuum Cruise Control

P0587 is particularly relevant to vehicles using older-style vacuum cruise-control systems.

In these systems, cruise-control operation depends on carefully controlling vacuum.

The basic process can be thought of as:

Cruise control activated → vacuum applied/maintained → actuator controls throttle → driver cancels or brake is applied → vacuum is released

The vent circuit is involved in that final release process.

If the electrical control of the vent valve is faulty, the system may disable cruise control to ensure that it can safely disengage.

P0587 and Electronic Throttle Vehicles

Many newer vehicles no longer rely on a traditional vacuum-operated cruise-control servo to control the throttle.

Instead, the engine control module can control the electronic throttle directly.

On such vehicles, a generic P0587 description may correspond to a different implementation of the cruise-control vent control circuit, or the vehicle may not use the same physical arrangement found on older systems.

Therefore, the exact vehicle-specific service information is extremely important.

P0587 vs P0586

These codes are closely related.

P0586 – Cruise Control Vent Control Circuit/Open

This indicates an open-circuit condition in the designated vent-control circuit.

P0587 – Cruise Control Vent Control Circuit Low

This indicates that the control module detects a low electrical condition.

In simplified terms:

• P0586 → circuit open

• P0587 → circuit voltage/signal low

• P0588 → circuit high

The exact diagnostic strategy depends on the vehicle's circuit design.

P0587 vs P0588

P0587 – Cruise Control Vent Control Circuit Low

The module detects an abnormally low electrical signal.

P0588 – Cruise Control Vent Control Circuit High

The module detects an abnormally high electrical signal.

This distinction can be useful when troubleshooting the wiring.

A P0587 condition may make a short-to-ground or low-voltage supply more suspicious, while P0588 may direct attention toward a short to voltage or another high-signal condition.

Related Cruise-Control Codes

Other cruise-control DTCs that may be relevant include:

• P0564 – Cruise Control Multi-Function Input "A" Circuit

• P0565 – Cruise Control On Signal

• P0566 – Cruise Control Off Signal

• P0567 – Cruise Control Resume Signal

• P0568 – Cruise Control Set Signal

• P0569 – Cruise Control Coast Signal

• P0570 – Cruise Control Accel Signal

• P0571 – Brake Switch "A" Circuit

• P0586 – Cruise Control Vent Control Circuit/Open

• P0587 – Cruise Control Vent Control Circuit Low

• P0588 – Cruise Control Vent Control Circuit High

• P0589 – Cruise Control Multi-Function Input "B" Circuit

• P0590 – Cruise Control Multi-Function Input "B" Circuit

When several cruise-control codes appear together, diagnosing the shared power supply, ground and wiring can be more productive than replacing individual components.

Common Diagnostic Mistakes

One common mistake is replacing the vent solenoid immediately after seeing P0587.

The solenoid may be faulty, but the code does not prove that it is.

Another mistake is confusing an electrical low-circuit fault with a vacuum-pressure problem.

A low electrical signal and low vacuum are two different diagnostic conditions.

Other common mistakes include:

• Ignoring the fuse

• Not checking the power supply

• Not checking for a short to ground

• Failing to inspect connectors

• Ignoring damaged wiring

• Assuming the system uses the same circuit as another vehicle

• Testing the solenoid without checking its control circuit

• Replacing the control module without testing the wiring

• Clearing the code without verifying the repair

How Do You Fix P0587?

The correct repair depends on what testing reveals.

Possible repairs include:

• Replacing a defective cruise-control vent solenoid

• Repairing a shorted wire

• Repairing broken wiring

• Replacing damaged connectors or terminals

• Restoring the correct power supply

• Replacing a blown fuse after identifying its cause

• Repairing a poor ground

• Repairing a vacuum hose or related mechanical component

• Correcting a control-module driver problem

• Replacing or programming a control module when properly diagnosed

The important principle is to repair the cause of the low circuit condition rather than simply replacing the component named in the code description.

Can You Clear P0587 With a Scanner?

Yes.

A suitable diagnostic scanner can normally clear P0587 from the control module's memory.

However, clearing the code does not repair the electrical fault.

If the circuit remains below the expected electrical range, the code will return after the control module performs its diagnostic checks.

After the repair:

1. Clear the stored DTC.

2. Activate the cruise-control system if the vehicle permits it.

3. Check the vent-control command and electrical signal.

4. Test cruise-control operation.

5. Road-test the vehicle safely.

6. Scan the vehicle again.

7. Confirm that P0587 does not return.

Final Thoughts on P0587

P0587 – Cruise Control Vent Control Circuit Low indicates that the control module has detected an abnormally low electrical condition in the circuit controlling the cruise-control vent function.

The most likely areas to investigate include the vent-control solenoid, wiring, connectors, fuse, power supply and possible short to ground.

On vehicles with vacuum-operated cruise control, the vent valve has an important safety function because it helps release cruise-control vacuum when the system needs to disengage. A vacuum leak can also affect cruise control, but it should not automatically be blamed for an electrical Circuit Low code.

The best approach is to diagnose the circuit systematically: check the codes, inspect the wiring and connectors, verify power and ground, test the solenoid, check the control signal, and only then investigate the control module. This prevents unnecessary parts replacement and provides a much more reliable repair.