Introduction:
The B1620 diagnostic trouble code (DTC) indicates a fault within the rear windshield wiper system of a vehicle. Specifically, it signals that the control module isn't receiving the expected signal from the rear wiper motor's low limit switch, suggesting an open circuit. This can lead to the rear wiper malfunctioning or failing to operate altogether, impacting rear visibility and potentially posing a safety concern.
Table: B1620 Wiper Rear Low Limit Input Circuit Open - Details and Troubleshooting
| Topic | Description | Possible Causes |
|---|---|---|
| Definition | The B1620 DTC signifies an open circuit in the rear wiper motor's low limit switch input circuit. The vehicle's control module (BCM/GEM) expects a specific voltage signal when the wiper arm is in its resting (low limit) position. When this signal is absent, the code is triggered. | Faulty rear wiper motor, wiring harness damage (open circuit, short to ground, short to voltage), corroded connectors, defective low limit switch, malfunctioning BCM/GEM. |
| Symptoms | Rear wiper not working, rear wiper working intermittently, rear wiper stuck in a position other than the park position, rear wiper operating continuously, B1620 DTC present. | |
| Low Limit Switch Function | The low limit switch is typically integrated into the rear wiper motor assembly. Its purpose is to signal the Body Control Module (BCM) or Generic Electronic Module (GEM) when the wiper arm is in its "parked" or resting position. This ensures the wiper stops in the correct location. | Switch failure, mechanical obstruction preventing the switch from closing, loose or corroded switch terminals. |
| Wiring Harness | The wiring harness connects the rear wiper motor, the low limit switch, and the BCM/GEM. It carries the electrical signals that control the wiper's operation and provide feedback to the module. | Broken or damaged wires, chafing against metal parts, poor connections at connectors, water intrusion causing corrosion. Specific wires to check include the signal wire from the low limit switch to the BCM/GEM. |
| Connectors | Connectors provide the physical connection points between the wiring harness and the various components of the rear wiper system. | Corrosion, loose pins, bent pins, damage due to improper handling. |
| BCM/GEM | The Body Control Module (BCM) or Generic Electronic Module (GEM) controls various body functions, including the rear wiper system. It receives input from the low limit switch and uses this information to control the wiper motor. | Internal module failure (rare), corrupted software, voltage supply issues to the module. |
| Testing Procedures | Visual inspection of wiring and connectors, multimeter testing for continuity and voltage, scan tool diagnostics to monitor sensor readings, wiring diagram analysis. | |
| Troubleshooting Steps | 1. Visual inspection. 2. Check for power and ground at the wiper motor. 3. Test the low limit switch for continuity. 4. Check continuity of the wiring between the switch and the BCM/GEM. 5. Test the BCM/GEM input signal. 6. Inspect and test the wiper motor itself. 7. Consider BCM/GEM replacement (last resort). | |
| Tools Required | Multimeter, scan tool, wiring diagrams, basic hand tools (screwdrivers, pliers, wire strippers), terminal test kit. | |
| Repair Procedures | Repair or replace damaged wiring, clean or replace corroded connectors, replace faulty low limit switch, replace faulty wiper motor, reprogram or replace BCM/GEM (if necessary). | |
| Related DTCs | Other wiper-related DTCs may be present, such as codes related to the rear wiper motor circuit, the front wiper system, or other BCM/GEM functions. These codes can provide additional clues to the underlying problem. | |
| Safety Precautions | Disconnect the battery before working on the electrical system. Use caution when working with electrical components. Consult the vehicle's repair manual for specific safety instructions. | |
| Location of Components | The rear wiper motor is typically located inside the rear hatch or liftgate. The BCM/GEM is usually located under the dashboard or in the center console. Consult the vehicle's repair manual for specific locations. | |
| Typical Voltage Readings | With the wiper in the park position, the low limit switch signal wire should read close to 0 volts (or ground). When the wiper is not in the park position, the voltage should be higher (typically battery voltage or a pull-up voltage). Refer to the vehicle's wiring diagram for specific values. | |
| Impact on Vehicle Operation | While not directly impacting engine performance, a malfunctioning rear wiper can significantly reduce rear visibility in inclement weather, increasing the risk of accidents. It can also be a nuisance. |
Detailed Explanations:
Definition: The B1620 code indicates an open circuit in the rear wiper motor's low limit switch input circuit. This means the Body Control Module (BCM) or Generic Electronic Module (GEM) isn't receiving the signal it expects when the wiper is in its parked, or "low limit," position. The absence of this signal tells the module that there's a problem with the circuit, prompting the code to be stored.
Symptoms: The most obvious symptom is a non-functional rear wiper. You might also observe the wiper operating intermittently, getting stuck in a position other than the park position, or even running continuously. The presence of the B1620 DTC confirmed by a scan tool is a key indicator.
Low Limit Switch Function: The low limit switch is a crucial component, typically integrated into the rear wiper motor assembly. It acts as a sensor that signals the BCM/GEM when the wiper arm has returned to its designated resting position. This is essential for ensuring the wiper stops correctly and doesn't obstruct the driver's view. Think of it as a "home" sensor for the wiper arm.
Wiring Harness: The wiring harness is the lifeline of the rear wiper system. It contains the wires that connect the wiper motor, the low limit switch, and the BCM/GEM, facilitating the flow of electrical signals that control the wiper's operation and provide feedback. Damage to this harness, such as broken wires or chafing, can disrupt the circuit and trigger the B1620 code.
Connectors: Connectors are the physical connection points where the wiring harness plugs into the various components of the rear wiper system. Corrosion, loose pins, or damage to these connectors can create an open circuit, preventing the signal from the low limit switch from reaching the BCM/GEM.
BCM/GEM: The Body Control Module (BCM) or Generic Electronic Module (GEM) is the brain of the operation. It controls various body functions, including the rear wiper system. It receives the signal from the low limit switch and uses this information to determine when to stop the wiper motor. While rare, a malfunctioning BCM/GEM can also be the cause of the B1620 code.
Testing Procedures: Diagnosing the B1620 code requires a systematic approach. This typically involves visual inspection of the wiring and connectors, multimeter testing for continuity and voltage, scan tool diagnostics to monitor sensor readings, and wiring diagram analysis to understand the circuit layout.
Troubleshooting Steps: A logical troubleshooting process is essential for efficiently resolving the issue. Start with a visual inspection for obvious damage. Then, check for power and ground at the wiper motor. Next, test the low limit switch for continuity to verify it's functioning. Check the continuity of the wiring between the switch and the BCM/GEM. Test the BCM/GEM input signal to see if it's receiving the signal from the switch. Inspect and test the wiper motor itself to rule out internal faults. Finally, consider BCM/GEM replacement as a last resort, as this is often the most expensive and complex repair.
Tools Required: A well-equipped toolbox is essential for tackling this repair. You'll need a multimeter to measure voltage and continuity, a scan tool to read DTCs and monitor sensor data, wiring diagrams to understand the circuit, basic hand tools (screwdrivers, pliers, wire strippers), and a terminal test kit to properly test connector pins.
Repair Procedures: The necessary repair will depend on the root cause of the problem. This might involve repairing or replacing damaged wiring, cleaning or replacing corroded connectors, replacing a faulty low limit switch, replacing a faulty wiper motor, or, in rare cases, reprogramming or replacing the BCM/GEM.
Related DTCs: Be aware that other wiper-related DTCs might be present, such as codes related to the rear wiper motor circuit, the front wiper system, or other BCM/GEM functions. These codes can provide valuable clues to help pinpoint the source of the problem and should be investigated alongside the B1620.
Safety Precautions: Always prioritize safety when working on vehicle electrical systems. Disconnect the battery before starting any repairs to prevent accidental shorts or electrical shock. Use caution when handling electrical components, and consult the vehicle's repair manual for specific safety instructions.
Location of Components: Knowing where the components are located is crucial for efficient troubleshooting. The rear wiper motor is typically located inside the rear hatch or liftgate. The BCM/GEM is usually located under the dashboard or in the center console. Refer to the vehicle's repair manual for precise locations specific to your vehicle model.
Typical Voltage Readings: Understanding expected voltage readings can help you diagnose the issue. With the wiper in the park position, the low limit switch signal wire should read close to 0 volts (or ground), indicating the switch is closed. When the wiper is not in the park position, the voltage should be higher (typically battery voltage or a pull-up voltage), indicating the switch is open. Always refer to the vehicle's wiring diagram for specific voltage values.
Impact on Vehicle Operation: While not directly affecting engine performance, a malfunctioning rear wiper can significantly reduce rear visibility in inclement weather, increasing the risk of accidents. It can also be a significant nuisance.
Frequently Asked Questions:
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What does the B1620 code mean? It indicates an open circuit in the rear wiper motor's low limit switch input circuit, meaning the control module isn't receiving the signal it expects when the wiper is in its parked position.
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Can I still drive my car with the B1620 code? Yes, you can usually still drive the car, but the rear wiper will likely not function correctly, which can impair rear visibility in bad weather.
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Is the B1620 code easy to fix? The difficulty varies depending on the cause. A simple wiring or connector issue is relatively easy to fix, while a faulty BCM/GEM is more complex.
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How much does it cost to fix the B1620 code? The cost depends on the repair needed. A simple wiring repair might cost under $100, while replacing the wiper motor or BCM/GEM can cost several hundred dollars.
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Can I fix the B1620 code myself? If you have basic automotive repair knowledge and tools, you can attempt to diagnose and repair the issue yourself. However, if you are not comfortable working with electrical systems, it's best to seek professional help.
Conclusion:
The B1620 DTC signals a problem with the rear wiper system's low limit switch circuit, typically indicating an open circuit. Thorough troubleshooting, starting with visual inspection and electrical testing, is crucial to identify and resolve the underlying issue, ensuring safe and effective rear visibility.