B1790 – Autolamp Sensor Input Circuit Failure

The ODBII code B1790 indicates a malfunction in the autolamp sensor input circuit, which may affect the automatic headlight control system.

The severity of ODBII code B1790 is generally considered moderate.

Common Causes For: B1789 Mirror Passenger Down Circuit Short To Ground

• Faulty autolamp sensor
• Damaged wiring or connectors
• Short circuit in the sensor circuit
• Open circuit in the sensor circuit
• Corroded connectors
• Faulty body control module (BCM)
• Poor ground connection

Common misdiagnosis for B1790 Autolamp Sensor Input Circuit Failure

• Faulty headlight switch
• Malfunctioning body control module (BCM)
• Defective autolamp sensor
• Wiring issues or shorts in the circuit
• Incorrectly diagnosed battery or charging system problems
• Faulty relay or fuse related to lighting
• Misinterpretation of other related codes or symptoms

Common Troubleshooting Steps

The OBD-II code B1790 refers to an “Autolamp Sensor Input Circuit Failure.” This code typically indicates a problem with the autolamp sensor circuit, which is responsible for detecting ambient light levels and controlling the vehicle’s automatic headlights. Here are some common troubleshooting steps to diagnose and resolve this issue:

• Check for Additional Codes: Use an OBD-II scanner to check for any other related trouble codes. This can provide more context and help identify if there are multiple issues.
• Inspect the Autolamp Sensor: Locate the autolamp sensor, which is usually mounted on the dashboard or windshield.
• Check for physical damage, dirt, or obstructions that may affect its operation.
• Examine Wiring and Connectors: Inspect the wiring harness and connectors associated with the autolamp sensor for signs of damage, corrosion, or loose connections.
• Repair or replace any damaged wiring or connectors.
• Test the Autolamp Sensor: If possible, test the autolamp sensor using a multimeter to check for proper voltage and resistance readings according to the manufacturer’s specifications.
• If the sensor is faulty, replace it.
• Check the Power and Ground Circuits: Verify that the autolamp sensor is receiving the correct voltage and that the ground circuit is functioning properly.
• Use a multimeter to check for power at the sensor connector when the vehicle is in the appropriate mode (e.g., ignition on).
• Inspect the Body Control Module (BCM): The BCM may be responsible for processing the signals from the autolamp sensor. Check for any faults or issues with the BCM.
• If necessary, reprogram or replace the BCM according to manufacturer guidelines.
• Clear the Codes and Test Drive: After performing repairs, clear the trouble codes using the OBD-II scanner.
• Take the vehicle for a test drive to see if the code reappears.
• Consult Service Manual: Refer to the vehicle’s service manual for specific diagnostic procedures and specifications related to the autolamp sensor and its circuit.
• Seek Professional Help: If the issue persists after performing the above steps, consider seeking assistance from a qualified mechanic or automotive technician who has experience with electrical systems and OBD-II diagnostics. By following these troubleshooting steps, you should be able to identify and resolve the issue related to the B1790 code.