P1585 - Cruise Control Inhibit Output Circuit

Introduction:

The P1585 diagnostic trouble code (DTC) indicates a problem with the Cruise Control Inhibit Output Circuit. This circuit is crucial for disengaging or preventing the cruise control system from engaging under specific conditions, such as when a brake is applied or a traction control event is detected. A malfunction in this circuit can lead to safety concerns and prevent the cruise control from functioning correctly, making diagnosis and repair essential.

Topic	Description	Potential Causes
Definition	Malfunction in the circuit that prevents/disengages cruise control.	Short to voltage or ground in the inhibit output circuit; open circuit in the inhibit output circuit; faulty cruise control module; faulty PCM (Powertrain Control Module); wiring harness damage; corroded connectors.
Symptoms	Cruise control does not engage; cruise control disengages unexpectedly; cruise control malfunction indicator lamp illuminated; other related DTCs present.	The most obvious symptom is the failure of the cruise control system to activate or maintain speed. The cruise control might engage briefly and then disengage. The check engine light or cruise control warning light may be illuminated on the dashboard. In some cases, other related DTCs concerning the brake system, throttle position, or vehicle speed may also be present. Erratic cruise control behavior (e.g., sudden acceleration or deceleration) is another potential symptom, although less common.
Diagnostic Procedure	Visual inspection; scan tool diagnostics; circuit testing; component testing.	Begin with a visual inspection of the wiring harness and connectors associated with the cruise control system, particularly the inhibit output circuit. Use a scan tool to retrieve all stored DTCs and freeze frame data. Perform a thorough circuit test using a multimeter to check for voltage, continuity, and resistance in the inhibit output circuit. Component testing may involve checking the functionality of the cruise control module and the PCM. Consult the vehicle's service manual for specific testing procedures and acceptable values.
Possible Solutions	Repair/replace wiring; repair/replace connectors; replace cruise control module; replace PCM; software update.	Repair any damaged or corroded wiring or connectors. Replace the cruise control module if it is found to be faulty. In rare cases, the PCM may be the cause of the problem and require replacement or reprogramming. A software update for the PCM or cruise control module might resolve the issue in some instances. Thoroughly test the system after each repair to ensure that the P1585 code does not return.
Affected Components	Cruise control module; PCM (Powertrain Control Module); Wiring harness; Connectors.	The cruise control module is the primary component responsible for controlling the cruise control system. The PCM plays a crucial role in managing various engine and transmission functions, including the cruise control system. The wiring harness and connectors provide the electrical pathways for communication between these components. Any damage or malfunction in these components can contribute to the P1585 code.
Related DTCs	P1580-P1589; P0500; P0501; other brake or throttle related codes.	The P1585 code is often accompanied by other related DTCs, such as P1580 through P1589 (cruise control system codes), P0500 (vehicle speed sensor malfunction), P0501 (vehicle speed sensor range/performance), and other brake or throttle-related codes. These codes can provide additional clues to the root cause of the problem. It is important to diagnose and address all related DTCs to ensure a complete and effective repair.
Severity	Moderate to High.	The severity of the P1585 code can range from moderate to high, depending on the specific circumstances. While the cruise control system may not be essential for vehicle operation, its malfunction can be inconvenient and potentially dangerous, especially on long drives. In some cases, a faulty cruise control system can lead to unexpected acceleration or deceleration, which can increase the risk of accidents. Therefore, it is recommended to address the P1585 code promptly to ensure safe and reliable vehicle operation.
Troubleshooting Tools	Multimeter; Scan tool; Wiring diagrams; Vehicle service manual.	A multimeter is essential for testing the voltage, continuity, and resistance of the circuits. A scan tool is used to retrieve DTCs and monitor live data. Wiring diagrams provide valuable information about the circuit layout and component locations. A vehicle service manual contains detailed diagnostic procedures and repair instructions.
Common Mistakes	Failing to inspect wiring; overlooking related DTCs; misdiagnosing PCM.	One of the most common mistakes is failing to thoroughly inspect the wiring harness and connectors for damage or corrosion. Overlooking related DTCs can lead to an incomplete diagnosis and ineffective repairs. Misdiagnosing the PCM as the source of the problem is another common mistake, as the PCM is often the last component to be considered. It is important to follow a systematic diagnostic approach and test all relevant components before replacing the PCM.
Component Location	Cruise control module (typically in the steering column or dashboard); PCM (typically under the hood).	The cruise control module is typically located in the steering column or dashboard. The PCM is usually located under the hood, often near the engine or firewall. Refer to the vehicle's service manual for the exact location of these components.

Detailed Explanations:

Definition: The P1585 code signifies a fault within the circuit responsible for preventing or disengaging the cruise control system. This circuit ensures that the cruise control is deactivated under specific conditions, like braking or traction loss, for safety reasons.

Symptoms: The most prominent symptom is the cruise control's inability to engage or maintain speed. This might be accompanied by the cruise control indicator light illuminating on the dashboard, or the system disengaging unexpectedly. Other related DTCs pertaining to the brake system or throttle position could also be present.

Diagnostic Procedure: The diagnostic process begins with a visual inspection of the wiring and connectors associated with the cruise control system. A scan tool is then used to retrieve DTCs and freeze frame data. Circuit testing with a multimeter is performed to check for voltage, continuity, and resistance. Component testing may involve assessing the cruise control module and PCM. Consult the vehicle’s service manual for specific procedures and acceptable values.

Possible Solutions: Addressing the P1585 code may involve repairing or replacing damaged wiring or connectors. If the cruise control module is faulty, it will need to be replaced. In rare cases, the PCM might be the culprit and require replacement or reprogramming. A software update for the PCM or cruise control module could also resolve the issue. Thorough testing after each repair is crucial to ensure the code does not return.

Affected Components: Key components involved include the cruise control module, the PCM (Powertrain Control Module), the wiring harness connecting these components, and the connectors that provide electrical connections. A fault in any of these components can trigger the P1585 code.

Related DTCs: The P1585 code may be accompanied by other related DTCs, such as P1580-P1589 (cruise control system codes), P0500 (vehicle speed sensor malfunction), P0501 (vehicle speed sensor range/performance), and other brake or throttle-related codes. These codes can provide valuable clues to the underlying cause of the problem.

Severity: The severity of the P1585 code can range from moderate to high. While cruise control is not essential for basic vehicle operation, its malfunction can be inconvenient and potentially dangerous. A faulty system could lead to unexpected acceleration or deceleration, increasing the risk of accidents.

Troubleshooting Tools: Essential tools for troubleshooting include a multimeter for electrical testing, a scan tool for retrieving DTCs and monitoring live data, wiring diagrams for understanding the circuit layout, and a vehicle service manual for detailed procedures and specifications.

Common Mistakes: Common mistakes include neglecting to inspect the wiring thoroughly, overlooking related DTCs, and prematurely diagnosing the PCM as the problem source. A systematic approach and thorough testing of all relevant components are crucial before replacing the PCM.

Component Location: The cruise control module is typically located in the steering column or dashboard area. The PCM is usually found under the hood, near the engine or firewall. Refer to the vehicle's service manual for the exact location of these components.

Frequently Asked Questions:

What does the P1585 code mean? It indicates a fault in the circuit that prevents or disengages the cruise control system.
Can I still drive my car with a P1585 code? Yes, but the cruise control won't function and there's a slight risk of unexpected behavior.
What are the most common causes of the P1585 code? Damaged wiring, faulty connectors, or a malfunctioning cruise control module are common culprits.
Is it expensive to fix a P1585 code? The cost varies depending on the cause; simple wiring repairs are inexpensive, but module replacement can be costly.
Can I fix the P1585 code myself? If you have experience with automotive electrical systems and diagnostic tools, you might be able to, but professional diagnosis is recommended.

Conclusion:

The P1585 diagnostic trouble code signifies a problem within the Cruise Control Inhibit Output Circuit, which is crucial for safe and reliable cruise control operation. Thorough diagnosis using appropriate tools and a systematic approach is essential for identifying and addressing the root cause of the problem, ensuring the cruise control system functions as intended.