Introduction:
The B1720 fault code indicates a problem within the mirror up and down control switch circuit in a vehicle. This circuit is responsible for allowing the driver to adjust the vertical position of the side mirrors for optimal visibility. Diagnosing and resolving this issue is crucial for safe driving, as it ensures the driver has a clear view of their surroundings.
Table: B1720 - Mirror Up and Down Control Switch Circuit
| Component/Aspect | Description | Potential Cause of B1720 |
|---|---|---|
| Mirror Control Switch | The physical switch in the driver's door or dashboard that allows the driver to control the mirror positions. It typically has multiple positions for selecting which mirror to control (left or right) and then up, down, left, and right movement. | Faulty Switch: Internal short, open circuit, or physical damage to the switch. Corrosion: Corrosion on the switch contacts preventing proper electrical flow. Loose Connection: Loose or disconnected wiring harness plugged into the switch. |
| Wiring Harness | The bundle of wires connecting the mirror control switch to the mirror motor and the vehicle's electrical system (usually through a body control module). | Open Circuit: A broken or cut wire in the harness. Short to Ground: A wire rubbing against the vehicle chassis causing a short circuit. Short to Voltage: A wire rubbing against another wire carrying voltage. Corrosion: Corrosion within the wiring harness connectors or along the wire itself. Damage: Physical damage to the harness (e.g., rodent damage, pinched wires). |
| Mirror Motor | The electric motor inside the side mirror assembly that physically moves the mirror glass up and down. | Motor Failure: Internal motor winding failure, worn brushes, or physical damage to the motor. Seized Motor: The motor is physically stuck and cannot move the mirror. Corrosion: Corrosion within the motor assembly, preventing proper operation. |
| Body Control Module (BCM) | A computer module that controls various electrical functions in the vehicle, including the mirror control system. Not all vehicles utilize the BCM for mirror control. | BCM Fault: The BCM is malfunctioning and not sending the correct signals to the mirror motor. Programming Issue: The BCM has lost its programming or has incorrect programming related to the mirror control function. BCM Input/Output Failure: Internal failure of the BCM preventing proper signal transmission to/from the mirror switch. |
| Power Supply/Ground | The power and ground circuits that provide electricity to the mirror control switch and motor. | Loss of Power: A blown fuse, a broken wire in the power supply circuit, or a faulty relay. Loss of Ground: A corroded or loose ground connection. |
| Diagnostic Trouble Code (DTC) Reader | A device used to read and clear DTCs, including B1720, from the vehicle's computer. | Misinterpretation of DTC: Incorrectly diagnosing the cause of the B1720 code due to relying solely on the code without further investigation. |
| Multimeter | A tool used to measure voltage, resistance, and continuity in electrical circuits. | Incorrect Usage: Using the multimeter incorrectly or misinterpreting the readings, leading to incorrect diagnosis. |
| Wiring Diagrams | Detailed schematics showing the wiring connections for the mirror control circuit. | Using Incorrect Diagram: Using a wiring diagram that does not match the specific make, model, and year of the vehicle. |
Detailed Explanations:
Mirror Control Switch: This is the primary interface for the driver to control the mirrors. It allows selecting which mirror (left or right) to adjust and then moving it up, down, left, or right. A faulty switch is a common cause of the B1720 code. Internal failures like short circuits or open circuits within the switch can prevent proper signal transmission. Corrosion on the contacts can also interrupt the electrical flow. Check for physical damage to the switch itself.
Wiring Harness: The wiring harness is the network of wires connecting the mirror control switch to the mirror motor and the vehicle's electrical system. Damage to the wiring harness, such as cuts, breaks, shorts, or corrosion, can disrupt the circuit and trigger the B1720 code. Carefully inspect the harness for any signs of damage, especially in areas where it may be exposed to the elements or physical stress. A common problem is rodent damage. Use a multimeter to check for continuity and shorts in the wires.
Mirror Motor: The mirror motor is responsible for physically moving the mirror glass. If the motor fails, either due to internal winding failure, worn brushes, or physical damage, the mirror will not move, and the B1720 code may be triggered. A seized motor, where the motor is physically stuck, can also cause this issue. Check the motor's power and ground connections before assuming the motor itself is faulty.
Body Control Module (BCM): In some vehicles, the BCM controls the mirror adjustment functions. A malfunctioning BCM, a programming issue within the BCM, or a failure of the BCM's input/output circuits can lead to the B1720 code. BCM issues are generally more complex to diagnose and may require specialized diagnostic equipment and expertise. Before suspecting the BCM, rule out simpler issues like switch, wiring, and motor problems.
Power Supply/Ground: The mirror control circuit needs a reliable power supply and ground connection to function correctly. A loss of power due to a blown fuse, a broken wire, or a faulty relay, or a loss of ground due to a corroded or loose connection can cause the B1720 code. Check the fuses related to the mirror control circuit first. Then, inspect the ground connections for corrosion or looseness.
Diagnostic Trouble Code (DTC) Reader: A DTC reader is essential for retrieving the B1720 code from the vehicle's computer. However, simply reading the code is not enough. A thorough diagnosis is required to pinpoint the root cause of the problem. Misinterpreting the DTC or relying solely on the code without further investigation can lead to incorrect repairs.
Multimeter: A multimeter is a crucial tool for diagnosing electrical problems in the mirror control circuit. It can be used to measure voltage, resistance, and continuity to identify open circuits, short circuits, and faulty components. However, it's important to use the multimeter correctly and interpret the readings accurately. Consult a wiring diagram and the vehicle's service manual for proper testing procedures.
Wiring Diagrams: Wiring diagrams provide detailed schematics of the mirror control circuit, showing the wiring connections between the switch, motor, BCM (if applicable), and power/ground sources. Using the correct wiring diagram for the specific make, model, and year of the vehicle is essential for accurate diagnosis. Incorrect wiring diagrams can lead to misdiagnosis and wasted time.
Frequently Asked Questions:
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What does the B1720 code mean? The B1720 code indicates a problem within the mirror up and down control switch circuit, meaning the mirror's vertical adjustment is malfunctioning.
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What are the common causes of the B1720 code? Common causes include a faulty mirror control switch, damaged wiring harness, failing mirror motor, or issues with the body control module (BCM).
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Can I fix the B1720 code myself? Depending on your mechanical skills, you may be able to diagnose and repair simpler issues like a faulty switch or damaged wiring. However, more complex problems may require professional assistance.
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How do I test the mirror control switch? Use a multimeter to check the switch for continuity and proper operation in each position, comparing your findings to the wiring diagram.
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Where can I find wiring diagrams for my vehicle? Wiring diagrams can be found in the vehicle's service manual, online databases, or through subscription services for automotive technicians.
Conclusion:
The B1720 code signifies a fault in the mirror up and down control switch circuit, potentially impacting driver visibility. A methodical approach to diagnosis, using a multimeter and wiring diagrams, is crucial for identifying and resolving the root cause. Consider seeking professional assistance if the problem is complex or beyond your skill level.