B0037: Dtc Auxiliary Switch Circuit Short to Ground
Diagnostic Trouble Code (DTC) B0037 indicates that the vehicle's control module has detected a short-to-ground condition in the Auxiliary (AUX) switch circuit. When this fault occurs, the voltage in the circuit drops below the expected range, causing the module to recognize an electrical problem and store the code.
Depending on the manufacturer, the AUX switch may control auxiliary lights, power outlets, off-road accessories, cooling fans, or other optional electrical equipment. A short-to-ground condition can prevent normal switch operation and may cause the accessory to remain permanently ON or OFF.
The exact description, circuit design, wire colors, connector locations, and diagnostic procedures may vary by vehicle make and model. Always consult the factory service information when available.
What Does B0037 Mean?
B0037 is generally defined as Auxiliary Switch Circuit Short to Ground. The control module monitors the AUX switch input and expects a specific voltage range. If the signal wire becomes directly connected to chassis ground or develops excessive resistance causing a low-voltage condition, the module interprets this as a circuit fault and stores DTC B0037.
In many vehicles, the AUX switch does not directly power the accessory. Instead, it sends an input signal to the Body Control Module (BCM) or another controller, which then commands a relay or output driver to operate the accessory.
How the AUX Switch Circuit Works
A typical AUX switch circuit receives power from the battery through a fuse. The switch input is monitored by a control module such as the BCM. When the driver presses the switch, the module detects a voltage change and performs the requested function. If the signal wire becomes shorted to ground, the voltage remains lower than expected and the module detects a fault condition.
Typical AUX Switch Circuit Block Diagram
Figure: Simplified AUX switch circuit. Actual circuit configuration may differ between manufacturers.
Common Symptoms of B0037
AUX Switch Does Not Respond
The switch may fail to activate the intended accessory because the control module cannot correctly interpret the switch signal.
Accessory Remains ON or OFF
Depending on circuit design, the accessory may remain permanently active or completely inoperative.
Stored Diagnostic Trouble Code
The BCM or related module stores B0037 and may illuminate a warning indicator if supported by the vehicle.
Intermittent Electrical Problems
Damaged wiring or loose connectors may cause the fault to appear only under certain driving conditions.
Common Causes of DTC B0037
Short to Ground in the Signal Wire
The most common cause of DTC B0037 is a signal wire that has rubbed against the vehicle body or another grounded metal component. This causes the circuit voltage to remain lower than expected.
Damaged AUX Switch
An internally failed AUX switch may create a permanent path to ground, causing the Body Control Module (BCM) to detect an abnormal input signal.
Damaged Wiring Harness
Broken insulation, pinched wires, rodent damage, or previous repair work can short the circuit to ground.
Loose or Corroded Connectors
Moisture, corrosion, or loose terminals may affect circuit voltage and create intermittent electrical faults.
Faulty Body Control Module (BCM)
Although uncommon, an internal BCM failure can incorrectly detect a short-to-ground condition after all other components have been verified.
How to Diagnose B0037 Using Live Data
A professional scan tool with Live Data capability can significantly reduce diagnostic time by allowing you to monitor the AUX switch input in real time.
Step 1 – Read All Diagnostic Trouble Codes
Perform a complete system scan and record all stored, pending, and history DTCs before clearing any codes. Related body control codes may help identify the root cause.
Step 2 – Monitor Live Data
Access the Body Control Module (BCM) and monitor parameters similar to:
- AUX Switch Status
- Auxiliary Switch Input
- Switch Request
- Input Voltage
- Battery Voltage
Operate the AUX switch while observing Live Data. Under normal conditions, the switch status should change between ON and OFF. If the value remains fixed, inspect the switch circuit and wiring.
Parameter names differ between scan tools and manufacturers. Some vehicles display AUX Switch Status, while others may use different names inside the BCM.
Step 3 – Perform an Active Test
If your scan tool supports Active Tests, command the AUX output ON and OFF. If the accessory responds correctly during the test but not when using the physical switch, the fault is likely located in the switch or its input circuit rather than the output circuit.
Electrical Testing
After completing the scan tool checks, perform electrical testing using a digital multimeter. Never replace the AUX switch or the Body Control Module (BCM) until the power supply, ground, and wiring have been verified.
Step 1 – Check the Fuse
Locate the fuse protecting the AUX switch circuit and verify continuity. Replace any blown fuse only after identifying and repairing the cause of the short circuit.
Step 2 – Verify Battery Voltage
With the ignition ON, measure the supply voltage at the AUX switch connector. A healthy circuit should normally have battery voltage on the power supply side. If voltage is missing, inspect the fuse, relay, and wiring harness.
Step 3 – Check for a Short to Ground
Disconnect the AUX switch and the BCM connector if required by the service manual. Measure continuity between the signal wire and chassis ground. If continuity exists when it should not, inspect the harness for damaged insulation or crushed wiring.
Step 4 – Inspect Connectors
Check all connectors for corrosion, bent terminals, moisture intrusion, loose locking tabs, or damaged pins. Connector problems are a common cause of intermittent body electrical faults.
Step 5 – Test the AUX Switch
Measure switch continuity while pressing and releasing the button. Compare the readings with the manufacturer's specifications. Replace the switch if it does not operate correctly.
Common Repairs for B0037
- Repair damaged wiring.
- Repair a short-to-ground condition.
- Replace a blown fuse after correcting the root cause.
- Clean or repair corroded connectors.
- Replace a faulty AUX switch.
- Repair or replace the relay if equipped.
- Reprogram or replace the BCM only after all other tests have been completed.
Common Diagnostic Mistakes
- Replacing the BCM before testing the wiring.
- Ignoring a damaged fuse or relay.
- Skipping Live Data analysis.
- Not inspecting connectors for corrosion.
- Clearing DTCs before recording Freeze Frame data.
- Assuming all manufacturers use the same AUX switch circuit design.
Most B0037 faults are caused by damaged wiring, poor connectors, or a faulty AUX switch—not by a failed BCM. Always complete the basic electrical tests before replacing expensive control modules.
Related Diagnostic Trouble Codes
- B0038 – Auxiliary Switch Circuit Short to Battery
- B0039 – Auxiliary Switch Circuit Open
- B0040 – Auxiliary Switch Circuit Performance
These DTCs are closely related to the AUX switch circuit and often share similar diagnostic procedures. However, always follow the manufacturer's service information because circuit design and fault detection logic vary between vehicle makes and models.
Frequently Asked Questions (FAQ)
Can I continue driving with DTC B0037?
In most cases, B0037 does not prevent the vehicle from being driven. However, the affected auxiliary accessory may not function correctly. The fault should be repaired as soon as possible to prevent further electrical issues.
Can a blown fuse cause B0037?
Yes. A blown fuse may interrupt the AUX switch circuit. However, a fuse usually blows because of an underlying electrical problem, such as a short to ground, which should be repaired before replacing the fuse.
Can a bad AUX switch trigger B0037?
Yes. An internally shorted or damaged AUX switch can pull the signal circuit to ground, causing the BCM to detect an abnormal voltage and store DTC B0037.
Is replacing the BCM the first repair step?
No. The BCM is rarely the root cause. Always inspect the fuse, wiring, connectors, relay, and AUX switch before considering BCM replacement or reprogramming.
Conclusion
DTC B0037 indicates that the control module has detected a short-to-ground condition in the AUX switch circuit. The most common causes include damaged wiring, a faulty AUX switch, poor electrical connections, or a blown fuse. Using a professional scan tool to analyze Live Data, combined with systematic electrical testing, helps identify the root cause quickly and prevents unnecessary replacement of expensive components.
Always repair the root cause of the short circuit before clearing diagnostic trouble codes. After completing the repair, clear the DTC and verify proper AUX switch operation with a road test and a final system scan.