B2559 — Aux A/C Blower Motor Relay Circuit Short to Battery #

Note: The wording of this Diagnostic Trouble Code (DTC) may differ depending on the vehicle manufacturer. Always refer to OEM (Original Equipment Manufacturer) documentation for precise terminology.

• “Auxiliary A/C Blower Motor Relay Circuit Short to Battery” (General/GM)
• “A/C Secondary Blower Relay Circuit High” (Ford)
• “Aux HVAC Blower Relay Circuit Shorted High” (Chrysler)

Summary of DTC B2559 #

The B2559 code signals that the vehicle’s onboard diagnostics have detected a short circuit to battery voltage within the auxiliary air conditioning (A/C) blower motor relay circuit. In plain terms, the system has found an unexpected direct battery connection where only controlled voltage should exist. This circuit controls the relay that powers the secondary or rear A/C blower motor, typically found in vehicles with multi-zone climate systems. When this code sets, it usually means the relay, its wiring, or a related component is inadvertently receiving constant 12V power, possibly due to a wiring fault or stuck relay. This condition can lead to continuous or failed operation of the auxiliary blower motor, affecting cabin comfort and potentially draining the battery.

Common Symptoms for Code B2559 #

If your vehicle is showing code B2559, you might notice changes in the performance of your auxiliary (rear) A/C blower. The system may behave unpredictably, or you may see warning lights or messages on your dashboard. Typical symptoms include:

• Auxiliary or rear A/C blower motor runs continuously, even with ignition off
• Blower motor does not operate when expected
• Battery drain or weak battery after the vehicle sits unused
• HVAC system warning lights or messages
• Loss of climate control in rear or secondary zones

Probable Causes for Code B2559 #

Several issues can trigger the B2559 code, most commonly relating to the relay or its circuit. Prioritizing the most frequent root causes:

1. Shorted auxiliary A/C blower relay (relay stuck closed or internally shorted)
2. Damaged or shorted wiring between relay and battery or control module
3. Corroded or contaminated relay socket causing unintended connection
4. Faulty auxiliary blower motor drawing excessive current or shorted to power
5. Control module malfunction (rare, but possible with repeated failures)

Step-by-Step Diagnostic for Code B2559 #

Diagnosing B2559 requires methodical checks of the relay circuit, wiring, and related components. Here are the recommended steps:

1. Scan for DTCs and note any related codes (especially HVAC or body control codes).
2. Visual inspection: Check the auxiliary A/C blower relay and its wiring harness for obvious damage, corrosion, or signs of overheating.
3. Test the relay: Remove the relay, inspect pins for discoloration, and bench-test it for proper open/close function.
4. Check for constant voltage: With the relay removed, use a multimeter to check for battery voltage at the control and load terminals. Unintended battery voltage here confirms a short.
5. Inspect wiring: Trace wiring between relay, blower motor, and control module for shorts to power, pinched wires, or melted insulation.
6. Check the blower motor: Disconnect the auxiliary blower motor and measure resistance for shorts internally.
7. Test control module output: If all else checks out, verify that the control module is not sending voltage when it shouldn’t.
8. Clear the code and retest: After each repair, clear DTCs and operate the system to confirm the fix.

Possible Repairs for Code B2559 #

The repair for B2559 depends directly on the root cause. Common fixes include:

• Replace a faulty or shorted auxiliary A/C blower relay
• Repair or replace damaged wiring or connectors in the relay circuit
• Clean or replace a corroded relay socket
• Replace an internally shorted auxiliary blower motor
• In rare cases, repair or replace the body control module (BCM) or HVAC control module

Is It Safe to Drive with Code B2559? #

Driving with code B2559 is generally safe for short periods, but caution is advised. While this fault won’t cause immediate drivability issues, it can lead to battery drain if the auxiliary blower runs continuously. If you notice persistent blower operation with the ignition off, disconnect the relay or blower fuse when parked to avoid a dead battery. Prolonged neglect may also result in loss of rear A/C, which could be uncomfortable for passengers in hot climates.

Vehicles Most Commonly Affected by Code B2559 #

Code B2559 appears most often in vehicles equipped with rear or auxiliary climate zones—typically larger SUVs, minivans, and some crossovers. Models from these manufacturers are frequently reported:

• GM (Chevrolet Suburban, Tahoe, GMC Yukon, Cadillac Escalade, etc.)
• Ford (Expedition, Explorer, Transit, etc.)
• Chrysler/Dodge (Town & Country, Grand Caravan, Pacifica, Durango, etc.)
• Toyota (Sienna, Sequoia, Land Cruiser with rear A/C)
• Honda (Odyssey, Pilot with rear climate systems)

Common Mistakes & Best Practices for Code B2559 #

Tackling B2559 can trip up even seasoned technicians if they rush or skip steps. Here are common pitfalls and tips for success:

• Replacing the blower motor or control module without first confirming the relay or wiring is at fault
• Ignoring signs of corroded relay sockets—which can cause repeat failures
• Testing circuits with the relay installed (always test with components removed to avoid false readings)
• Not checking TSBs (Technical Service Bulletins) for known wiring harness issues on your specific vehicle
• Always disconnect the battery before probing relay circuits to prevent accidental shorts

FAQ Express for Code B2559 #

Still have questions about B2559? Here are quick answers to common concerns:

• Q: Can I just pull the relay to stop the blower motor drain?
  A: Yes, removing the relay will interrupt power to the auxiliary blower, preventing battery drain as a temporary fix until repairs are made.
• Q: Will clearing the code fix the problem?
  A: No. The code will return unless the underlying short or relay fault is corrected. Always address the root cause before clearing DTCs.