Introduction
The B2559 diagnostic trouble code (DTC) indicates a "Aux A/C Blower Motor Relay Circuit Short to Battery." This means the vehicle's computer (ECU or PCM) has detected an unintended voltage on the circuit controlling the auxiliary air conditioning blower motor relay. This condition can prevent the auxiliary A/C blower from operating correctly, leading to discomfort for passengers, especially in larger vehicles with rear A/C systems. Diagnosing and resolving this issue promptly is crucial for maintaining a comfortable cabin environment and preventing potential damage to electrical components.
B2559 Aux A/C Blower Motor Relay Circuit: Key Information
| Topic | Description | Potential Causes |
|---|---|---|
| Definition | DTC B2559 indicates the auxiliary A/C blower motor relay circuit is experiencing a short to battery voltage. | Damaged wiring harness: Frayed, cracked, or rodent-chewed wires. |
| The control circuit is receiving voltage when it shouldn't, typically due to compromised insulation or internal component failure. | Shorted relay: Internal failure within the auxiliary A/C blower motor relay causing it to constantly receive power. | |
| This fault prevents the vehicle's computer from properly controlling the auxiliary A/C blower motor. | Faulty ECU/PCM: (Rare) Internal failure within the Engine Control Unit/Powertrain Control Module causing it to send incorrect voltage signals. | |
| Damaged connector: Corroded or loose connections at the relay, wiring harness, or ECU/PCM. | ||
| Pinched or chaffed wiring: Areas where the wiring harness rubs against metal parts of the vehicle, causing insulation damage. | ||
| Symptoms | Auxiliary A/C blower motor may run constantly, even when the system is turned off. | Auxiliary A/C blower motor may not operate at all. |
| Battery drain due to the constantly running blower motor. | Check Engine Light (MIL) illuminated. | |
| Auxiliary A/C system malfunction. | Possible burning smell if the short is severe and causing overheating of the wiring. | |
| Diagnostic Procedure | Visual inspection of wiring harness and connectors for damage. | Use a multimeter to test the voltage at the auxiliary A/C blower motor relay circuit. Verify voltage at the relay pin meant to be switched by the ECU/PCM. |
| Check the auxiliary A/C blower motor relay itself for proper operation. | Use a scan tool to monitor the status of the auxiliary A/C blower motor control signal from the ECU/PCM. | |
| Perform a wiggle test on the wiring harness while monitoring the relay circuit voltage to identify intermittent shorts. | Consult vehicle-specific wiring diagrams to trace the circuit. | |
| Repair Strategies | Repair or replace damaged wiring harness sections. | Replace the auxiliary A/C blower motor relay. |
| Clean and secure corroded or loose connectors. | Secure wiring harnesses to prevent future chafing. | |
| In rare cases, replace the ECU/PCM. (This should be a last resort after all other possibilities have been ruled out). | ||
| Related DTCs | Other A/C system related codes, such as those related to the A/C compressor or refrigerant pressure. | Codes related to other electrical components sharing the same power supply or ground. |
| Tools Required | Multimeter, Scan Tool, Wiring Diagrams, Wire Strippers, Crimpers, Electrical Tape, Connector Cleaner. | |
| Safety Precautions | Disconnect the negative battery terminal before working on electrical components. | Be careful when working around sharp edges or hot surfaces. |
| Wear appropriate safety glasses and gloves. | ||
| Circuit Description | The auxiliary A/C blower motor relay is typically controlled by the ECU/PCM, which grounds the relay coil to activate the blower motor. | A short to battery in the control circuit provides voltage to the relay coil, bypassing the ECU/PCM control. |
| Component Location | The auxiliary A/C blower motor relay location varies depending on the vehicle make and model. Consult the vehicle's service manual. | Common locations include the engine compartment fuse box, under the dashboard, or near the auxiliary A/C unit. |
| Voltage Readings | Normal voltage readings on the control circuit should be close to battery voltage when the ECU/PCM is not commanding the blower motor on, and near 0 volts when the ECU/PCM is commanding the blower motor on. | A short to battery will show battery voltage on the control circuit even when the ECU/PCM is not commanding the blower motor on. |
| Common Wire Colors | Wire colors vary by manufacturer and model. Refer to the vehicle's wiring diagram for specific wire colors. | |
| Potential for Damage | Constant operation of the auxiliary A/C blower motor can overheat and damage the motor. | Battery drain can lead to a dead battery. |
| A severe short can cause damage to the ECU/PCM. | ||
| Level of Difficulty | Intermediate. Requires basic electrical troubleshooting skills and knowledge of automotive wiring. |
Detailed Explanations
Definition: DTC B2559 signals that the circuit controlling the auxiliary A/C blower motor relay has an unintended connection to the vehicle's battery voltage. This means the circuit is receiving voltage when it shouldn't be, likely due to damaged wiring or a faulty component. The ECU/PCM is unable to control the blower motor correctly, leading to operational issues.
Symptoms: The most common symptom is the auxiliary A/C blower motor running constantly, even when the system is switched off. Conversely, the blower may not operate at all. This can lead to a noticeable battery drain and the illumination of the Check Engine Light. A burning smell might be present if the short is severe and causing overheating.
Diagnostic Procedure: Start with a visual inspection of the wiring harness and connectors associated with the auxiliary A/C blower motor relay. Use a multimeter to test the voltage at the relay control circuit. Check the relay itself for proper function. A scan tool can be used to monitor the ECU/PCM's control signal. A "wiggle test" can help identify intermittent shorts. Consulting vehicle-specific wiring diagrams is crucial for tracing the circuit.
Repair Strategies: The most common repair is to repair or replace damaged sections of the wiring harness. Replacing the auxiliary A/C blower motor relay is another common solution. Clean and secure any corroded or loose connectors. Secure the wiring harness to prevent future chafing. In rare cases, the ECU/PCM may need replacement, but this should be a last resort.
Related DTCs: This code might be accompanied by other A/C system-related codes, such as those pertaining to the A/C compressor or refrigerant pressure. Also, look for codes related to other electrical components that share the same power supply or ground, as this could indicate a broader electrical issue.
Tools Required: Essential tools include a multimeter for voltage and resistance testing, a scan tool for reading DTCs and monitoring sensor data, wiring diagrams for circuit tracing, wire strippers and crimpers for wiring repairs, electrical tape for insulation, and connector cleaner for cleaning corroded connections.
Safety Precautions: Always disconnect the negative battery terminal before working on electrical components to prevent electrical shock and potential damage to the vehicle's electrical system. Be mindful of sharp edges and hot surfaces in the engine compartment. Wear safety glasses and gloves for added protection.
Circuit Description: The auxiliary A/C blower motor relay is typically controlled by the ECU/PCM. The ECU/PCM provides a ground to the relay coil to activate the blower motor. A short to battery in the control circuit provides voltage to the relay coil, bypassing the ECU/PCM's control. This causes the blower motor to run even when it's not supposed to.
Component Location: The exact location of the auxiliary A/C blower motor relay varies depending on the vehicle make and model. Common locations include the engine compartment fuse box, under the dashboard, or near the auxiliary A/C unit itself. Consult the vehicle's service manual for the precise location.
Voltage Readings: Under normal operation, the control circuit should show close to battery voltage when the ECU/PCM is not commanding the blower motor on, and near 0 volts when the ECU/PCM is commanding the blower motor on. With a short to battery, the control circuit will show battery voltage even when the ECU/PCM is not commanding the blower motor on.
Common Wire Colors: Wire colors vary significantly between manufacturers and even different models within the same manufacturer. Always refer to the vehicle's wiring diagram for accurate wire color identification.
Potential for Damage: Continuous operation of the auxiliary A/C blower motor can lead to overheating and premature failure of the motor. Battery drain can result in a dead battery. In severe cases, a short can cause damage to the ECU/PCM itself.
Level of Difficulty: Diagnosing and repairing a B2559 code is generally considered an intermediate-level task. It requires basic electrical troubleshooting skills, familiarity with automotive wiring, and the ability to read and interpret wiring diagrams.
Frequently Asked Questions
What does the B2559 code mean? It means there's a short to battery in the auxiliary A/C blower motor relay circuit, causing unintended voltage on the control circuit.
Can I drive with a B2559 code? Driving is possible, but the auxiliary A/C may not function correctly, and the battery could drain if the blower runs constantly. It's best to address the issue promptly.
What's the most common cause of a B2559 code? Damaged wiring or a faulty relay are the most frequent culprits.
How do I fix a B2559 code? Repairing damaged wiring, replacing the relay, or cleaning corroded connections are common solutions.
Do I need a special tool to diagnose a B2559 code? A multimeter and wiring diagrams are essential. A scan tool can also be helpful.
Conclusion
The B2559 DTC points to a short to battery in the auxiliary A/C blower motor relay circuit, which can cause operational problems and potential damage. Thorough diagnosis and repair, starting with a visual inspection and progressing to electrical testing, are crucial for resolving this issue and restoring proper A/C function.