The P1555 diagnostic trouble code (DTC) indicates a malfunction within the Electronic Variable Orifice (EVO) system. This system, primarily found in power steering systems, adjusts the steering assist based on vehicle speed, providing lighter steering at low speeds for easier maneuvering and firmer steering at higher speeds for improved stability. A P1555 code suggests a problem with the output signal from the EVO system, potentially affecting steering performance and driver safety.
P1555 Code: Comprehensive Information Table
| Aspect | Description | Possible Causes |
|---|---|---|
| Definition | Electronic Variable Orifice (EVO) Output Malfunction. Signifies an issue with the signal being sent from the EVO system, typically related to the solenoid valve controlling power steering fluid flow or the wiring associated with it. | Open or short circuit in the EVO solenoid valve wiring. Defective EVO solenoid valve. Faulty Power Steering Control Module (PSCM). Low power steering fluid level. Air in the power steering system. Mechanical failure within the power steering pump. Corroded or damaged connectors. |
| Symptoms | Erratic or inconsistent power steering assist. Stiff steering at low speeds. Overly sensitive steering at high speeds. Power steering warning light illumination. Unusual noises from the power steering pump. Vehicle pulling to one side. Complete loss of power steering assist. | N/A |
| Common Causes | Wiring issues (shorts, opens, corrosion). Defective EVO solenoid valve. Faulty Power Steering Control Module (PSCM). Low power steering fluid. Air in the system. Mechanical pump failure. | N/A |
| Diagnostic Steps | Visual inspection of wiring and connectors. Checking power steering fluid level and condition. Testing the EVO solenoid valve for proper resistance and operation. Scanning the PSCM for other related DTCs. Performing a power steering system pressure test. Using a multimeter to check voltage and ground signals at the EVO solenoid valve connector. Inspecting the power steering pump for leaks or damage. | N/A |
| Possible Solutions | Repair or replacement of damaged wiring and connectors. Replacement of the EVO solenoid valve. Replacement of the Power Steering Control Module (PSCM) (requires programming). Adding power steering fluid to the correct level. Bleeding the power steering system to remove air. Replacement of the power steering pump. Flushing the power steering system. | N/A |
| Affected Systems | Power Steering System, specifically the Electronic Variable Orifice (EVO) control mechanism. Power Steering Control Module (PSCM). Engine Control Unit (ECU) if integrated. | N/A |
| Related DTCs | P0551 (Power Steering Pressure Sensor Circuit Range/Performance), P0552 (Power Steering Pressure Sensor Circuit Low Input), P0553 (Power Steering Pressure Sensor Circuit High Input), specific manufacturer codes related to power steering system malfunctions. | N/A |
| Severity | Moderate to High. A P1555 code can significantly impact steering control and driver safety, especially at higher speeds. Address the issue promptly. | N/A |
| Tools Required | OBD-II scanner, Multimeter, Power steering fluid, Wrenches, Sockets, Wire strippers, Wire crimpers, Test light, Pressure gauge (for power steering system). | N/A |
| Average Repair Cost | Varies significantly depending on the cause. Wiring repair can be relatively inexpensive. EVO solenoid valve replacement can range from $100-$300. PSCM replacement can be more costly, potentially exceeding $500, including programming. Power Steering Pump replacement can also vary $200-$600. | N/A |
| Vehicle Applications | General Motors (GM) vehicles (Chevrolet, GMC, Buick, Cadillac) are commonly associated with this code, but it can appear in other manufacturers using similar electronically controlled power steering systems. | N/A |
| System Operation | The EVO system utilizes a solenoid valve to regulate the flow of power steering fluid. The PSCM controls the solenoid valve based on inputs like vehicle speed. At low speeds, the solenoid restricts fluid flow, increasing steering assist. At high speeds, the solenoid opens, reducing assist for a firmer feel. | N/A |
| Solenoid Valve Testing | Disconnect the solenoid valve connector. Use a multimeter to measure the resistance across the solenoid valve terminals. Compare the reading to the manufacturer's specifications. An open circuit (infinite resistance) or a short circuit (close to zero resistance) indicates a faulty solenoid valve. You can also apply power and ground to the solenoid to see if it clicks, indicating it's functioning. | N/A |
| Wiring Diagram Importance | Obtain a vehicle-specific wiring diagram for the EVO system. This diagram will show the location of the EVO solenoid valve, the PSCM, and all associated wiring. It will also help you identify the correct wires to test for voltage, ground, and continuity. | N/A |
| PSCM Programming | If the Power Steering Control Module (PSCM) is replaced, it will likely require programming to match the vehicle's specific configuration. This programming is typically performed by a qualified technician using specialized diagnostic equipment. Failing to program the PSCM can result in continued power steering issues and potentially other DTCs. | N/A |
Detailed Explanations
Definition: The P1555 code indicates a problem with the Electronic Variable Orifice (EVO) system's output signal. This means the system isn't communicating correctly, often pointing to issues with the solenoid valve or its wiring. The EVO system is critical for adjusting power steering assist based on vehicle speed.
Symptoms: The most common symptom is erratic or inconsistent power steering assist. You might experience stiff steering at low speeds or overly sensitive steering at high speeds. The power steering warning light may also illuminate. Other symptoms include unusual noises from the power steering pump or the vehicle pulling to one side. In severe cases, you might experience a complete loss of power steering.
Common Causes: The most frequent causes include wiring issues such as shorts, opens, or corrosion in the EVO solenoid valve circuit. A defective EVO solenoid valve itself is also a common culprit. Other potential causes include a faulty Power Steering Control Module (PSCM), low power steering fluid, air in the system, or mechanical failure within the power steering pump.
Diagnostic Steps: Start with a visual inspection of the wiring and connectors associated with the EVO solenoid valve. Check the power steering fluid level and condition. Use an OBD-II scanner to check for any other related DTCs. Test the EVO solenoid valve for proper resistance and operation using a multimeter. Perform a power steering system pressure test to check for mechanical issues. A wiring diagram can be very helpful in tracing the circuits.
Possible Solutions: Depending on the diagnosis, solutions may include repairing or replacing damaged wiring and connectors. Replacing the EVO solenoid valve is a common fix. In some cases, the Power Steering Control Module (PSCM) may need to be replaced, which requires programming. Adding power steering fluid or bleeding the system to remove air can also resolve the issue. In cases of pump failure, replacement is necessary. Consider flushing the power steering system to remove contaminants.
Affected Systems: The primary system affected is the Power Steering System, specifically the Electronic Variable Orifice (EVO) control mechanism. The Power Steering Control Module (PSCM) and, in some cases, the Engine Control Unit (ECU), which may be integrated with the PSCM, are also involved.
Related DTCs: Other DTCs that might accompany a P1555 code include P0551 (Power Steering Pressure Sensor Circuit Range/Performance), P0552 (Power Steering Pressure Sensor Circuit Low Input), P0553 (Power Steering Pressure Sensor Circuit High Input), as well as manufacturer-specific codes related to power steering malfunctions.
Severity: A P1555 code is considered moderately to highly severe. Because it affects steering control, it can compromise driver safety, especially at higher speeds. It is important to address this issue promptly.
Tools Required: To diagnose and repair a P1555 code, you will need an OBD-II scanner to read the code, a multimeter to test electrical components, power steering fluid, wrenches, sockets, wire strippers, wire crimpers, a test light, and a pressure gauge for the power steering system.
Average Repair Cost: The repair cost can vary significantly. Simple wiring repairs are relatively inexpensive. EVO solenoid valve replacement typically ranges from $100 to $300. PSCM replacement, including programming, can be more costly, potentially exceeding $500. A Power Steering Pump replacement can also vary depending on the vehicle and parts supplier $200-$600.
Vehicle Applications: This code is commonly found in General Motors (GM) vehicles such as Chevrolet, GMC, Buick, and Cadillac. However, it can appear in other manufacturers using similar electronically controlled power steering systems.
System Operation: The EVO system uses a solenoid valve to regulate the flow of power steering fluid. The PSCM controls this valve based on inputs like vehicle speed. At low speeds, the solenoid restricts fluid flow, increasing steering assist for easier maneuvering. At high speeds, the solenoid opens, reducing assist for a firmer feel and improved stability.
Solenoid Valve Testing: To test the solenoid valve, disconnect the connector and use a multimeter to measure the resistance across the terminals. Compare this reading to the manufacturer's specifications. An open or short circuit indicates a faulty valve. You can also apply power and ground to the solenoid to see if it clicks, indicating it's functioning mechanically.
Wiring Diagram Importance: A vehicle-specific wiring diagram is crucial for diagnosing a P1555 code. It shows the location of the EVO solenoid valve, the PSCM, and all associated wiring, helping you identify the correct wires to test for voltage, ground, and continuity.
PSCM Programming: When replacing the Power Steering Control Module (PSCM), it will likely require programming to match the vehicle's specific configuration. This is typically done by a qualified technician using specialized diagnostic equipment. Failing to program the PSCM can lead to continued power steering issues and potentially other DTCs.
Frequently Asked Questions
What does the P1555 code mean? The P1555 code indicates a problem with the Electronic Variable Orifice (EVO) system output, typically related to the solenoid valve or its wiring.
Can I drive with a P1555 code? Driving with a P1555 code is not recommended, as it can affect steering control and safety, especially at higher speeds.
What is the most common cause of a P1555 code? The most common cause is wiring issues, such as shorts, opens, or corrosion in the EVO solenoid valve circuit.
How do I fix a P1555 code? Fixing a P1555 code involves diagnosing the root cause, which may require repairing wiring, replacing the EVO solenoid valve, or replacing the PSCM.
Do I need a special tool to diagnose a P1555 code? Yes, you will need an OBD-II scanner to read the code and a multimeter to test electrical components. A wiring diagram will also be very helpful.
Conclusion
The P1555 code signifies a malfunction within the Electronic Variable Orifice (EVO) system, impacting steering performance and potentially driver safety. Proper diagnosis, using a methodical approach and the right tools, is crucial for identifying the root cause and implementing the appropriate repair, whether it involves wiring repairs, component replacement, or system adjustments. Resolving this issue promptly ensures optimal steering control and a safer driving experience.