Introduction
The B1820 diagnostic trouble code (DTC) signifies a "Wiper Rear Motor Up Relay Coil Circuit Short to Battery." This means the vehicle's computer, often the Body Control Module (BCM), has detected an unintended voltage level in the circuit controlling the relay coil that activates the rear wiper motor in the "up" or high-speed position. This electrical fault can prevent the rear wiper from functioning correctly, potentially impairing visibility in adverse weather conditions. Understanding the causes, symptoms, and diagnostic procedures for a B1820 code is crucial for effective troubleshooting and repair.
Table: B1820 Wiper Rear Motor Up Relay Coil Circuit Short to Battery
| Topic | Description | | Code Definition | Explanation of the B1820 code and what it signifies. within the automotive industry, specifically when dealing with diagnostic trouble codes (DTCs). It highlights a specific electrical fault related to the rear wiper motor system, which is essential for maintaining visibility and safety while driving. Correct diagnosis and repair of this issue can improve driving safety.
Detailed Explanations
Code Definition
The B1820 code, as mentioned, refers to a "Wiper Rear Motor Up Relay Coil Circuit Short to Battery." This means the vehicle's computer (typically the BCM) has detected a higher than expected voltage level on the control circuit for the "up" or high-speed relay coil that powers the rear wiper motor. The relay coil is designed to activate the relay contacts when energized, completing the circuit to the rear wiper motor. A "short to battery" indicates that the wiring or components in this circuit are making unintended contact with a power source (typically the vehicle's battery voltage), causing excessive current flow and triggering the DTC.
Possible Causes
- Damaged Wiring: This is one of the most common causes. Inspect the wiring harness that runs to the rear wiper motor and relay. Look for chafed, cracked, or otherwise damaged insulation that could allow the wire to short to a positive voltage source. Pay close attention to areas where the harness passes through the vehicle's body or is routed near sharp edges.
- Faulty Relay: The rear wiper motor up relay itself could be internally shorted. This can occur due to age, corrosion, or physical damage.
- Short in the Wiper Motor: Although less common, a short within the rear wiper motor itself could backfeed voltage into the relay control circuit.
- BCM Malfunction: In rare cases, a faulty BCM could be incorrectly diagnosing the circuit or even causing the short itself. This is usually a diagnosis of last resort after other potential causes have been ruled out.
- Corroded Connectors: Corrosion within the connectors of the relay, wiper motor, or wiring harness can create a conductive path, leading to a short to battery.
Symptoms
- Rear Wiper Not Working: This is the most obvious symptom. The rear wiper might not operate at all, or it may only work intermittently.
- Rear Wiper Stuck On: The rear wiper might be constantly running, even when the switch is off, due to the constant voltage being applied to the motor.
- Blown Fuses: The short circuit may cause the fuse protecting the rear wiper circuit to blow repeatedly. Replacing the fuse without addressing the underlying short will only result in the fuse blowing again.
- BCM Issues: In some cases, the BCM may exhibit other issues if the short is severe or prolonged. This is less common but should be considered if other electrical problems are present.
- DTC Present: The B1820 code will be stored in the vehicle's computer and can be retrieved using a scan tool.
Diagnostic Steps
- Retrieve DTCs: Use a scan tool to confirm the presence of the B1820 code and check for any other related codes.
- Inspect Wiring and Connectors: Visually inspect the wiring harness and connectors associated with the rear wiper motor and relay. Look for any signs of damage, corrosion, or chafing. Pay particular attention to areas where the harness is routed near moving parts or sharp edges.
- Check Fuses: Verify that the fuse protecting the rear wiper circuit is intact. If the fuse is blown, replace it with a fuse of the correct amperage. If the fuse blows again immediately, this confirms the presence of a short circuit.
- Test the Relay:
- Relay Swap: If possible, swap the rear wiper motor up relay with a known good relay from another circuit (e.g., a similar relay used for the horn or headlights). If the B1820 code disappears and the swapped circuit now has problems, the original relay is likely faulty.
- Relay Testing: Use a multimeter to test the relay's coil resistance and contact continuity. A shorted coil or faulty contacts can indicate a bad relay. Refer to the vehicle's wiring diagram for the correct pinout and expected resistance values.
- Isolate the Circuit:
- Disconnect the Wiper Motor: Disconnect the rear wiper motor connector. If the B1820 code disappears after disconnecting the motor, the short is likely within the motor itself.
- Disconnect the Relay: Disconnect the rear wiper motor up relay. If the B1820 code remains, the short is likely in the wiring between the relay and the BCM.
- Perform Voltage and Continuity Tests:
- Voltage Test: With the relay disconnected and the ignition on, use a multimeter to check for voltage on the relay coil control circuit. If voltage is present when it shouldn't be, this confirms a short to battery.
- Continuity Test: With the battery disconnected, use a multimeter to check for continuity between the relay coil control circuit and ground. If continuity is present, this indicates a short to ground.
- Component Replacement: Based on the diagnostic findings, replace the faulty component (wiring, relay, wiper motor, or BCM).
Repair Procedures
- Wiring Repair: If damaged wiring is found, repair or replace the affected section of the harness. Use proper splicing techniques and ensure the repair is well-insulated to prevent future shorts.
- Relay Replacement: If the relay is faulty, replace it with a new relay of the correct type and specification.
- Wiper Motor Replacement: If the wiper motor is shorted, replace it with a new or remanufactured motor.
- BCM Replacement/Reprogramming: If the BCM is faulty, it may need to be replaced and reprogrammed. This is a complex procedure that should be performed by a qualified technician.
Tools Required
- Scan Tool: To retrieve and clear DTCs.
- Multimeter: To perform voltage, continuity, and resistance tests.
- Wiring Diagram: To understand the circuit layout and identify components.
- Wire Strippers and Crimpers: For wiring repairs.
- Electrical Tape or Heat Shrink Tubing: For insulating wiring repairs.
- Basic Hand Tools: Screwdrivers, pliers, sockets, etc.
Frequently Asked Questions
What does the B1820 code mean? The B1820 code indicates a "Wiper Rear Motor Up Relay Coil Circuit Short to Battery," meaning the vehicle's computer has detected an unintended voltage level in the rear wiper motor relay control circuit.
Can I fix this problem myself? Depending on your mechanical and electrical skills, you may be able to diagnose and repair the problem yourself. However, it is recommended to consult a qualified technician if you are not comfortable working with electrical systems.
What are the common causes of the B1820 code? Common causes include damaged wiring, a faulty relay, a short in the wiper motor, or a BCM malfunction.
How do I test the rear wiper motor relay? You can test the relay by swapping it with a known good relay or using a multimeter to check its coil resistance and contact continuity.
Will this affect the safety of my vehicle? A malfunctioning rear wiper can impair visibility in adverse weather conditions, potentially affecting safety.
Conclusion
The B1820 DTC indicates a short to battery in the rear wiper motor up relay coil circuit, requiring careful diagnosis and repair. Addressing this issue promptly is essential for maintaining optimal visibility and safe driving conditions. Remember to always consult the vehicle's service manual and wiring diagrams for specific troubleshooting procedures and component locations.