B1820 — Wiper Rear Motor Up Relay Coil Circuit Short To Battery #

Note: The description of DTC B1820 may vary depending on the vehicle manufacturer. Always consult OEM service information for your specific application.

• B1820: Rear Wiper Motor Relay Circuit Short to Battery (Ford)
• B1820: Rear Wiper Motor Up Relay Coil Circuit Short to Battery (General Motors)
• B1820: Rear Wiper Relay Short Circuit (Toyota)
• B1820: Rear Wiper Relay Circuit High (Nissan)

Summary of DTC B1820 #

The B1820 diagnostic trouble code (DTC) indicates that the vehicle’s onboard diagnostic system has detected a short circuit to battery voltage in the rear wiper motor up relay coil circuit. In simpler terms, this means that the electrical path that controls the rear wiper’s upward movement relay is receiving full battery voltage when it shouldn’t, suggesting a wiring fault or component malfunction. This code is specific to the body control module (BCM) and typically does not affect core drivability, but it can lead to non-functionality or erratic behavior of the rear wiper system. Addressing this issue promptly ensures safe visibility and prevents further electrical complications.

Common Symptoms for Code B1820 #

When B1820 is active, you may notice some distinct symptoms related to the rear wiper operation. While the vehicle will remain drivable, a malfunctioning rear wiper can compromise rear visibility, especially during adverse weather. Here’s what drivers and technicians often report:

• Rear wiper does not operate in the “up” or “park” position
• Rear wiper cycles erratically or does not stop at the correct position
• Intermittent or complete loss of rear wiper function
• Illuminated warning light (such as a body or electrical fault indicator) on the dashboard
• Possible BCM-related warning messages

Probable Causes of B1820 (Ranked by Likelihood) #

Diagnosing B1820 means considering several possible causes, but some are more common than others. Typically, issues originate from wiring faults, relay failures, or even water intrusion. Here are the most likely causes, ranked in order of frequency:

1. Damaged, shorted, or chafed wiring harness to the rear wiper relay or motor
2. Failed rear wiper up relay (relay coil shorted internally)
3. Corroded or water-damaged connectors at the rear wiper assembly or relay block
4. Faulty rear wiper motor drawing excessive current or shorted internally
5. Defective body control module (BCM) (rare, but possible)

Step-by-Step Diagnostic for Code B1820 #

A methodical approach is essential for diagnosing B1820. Rushing can lead to misdiagnosis or unnecessary part replacement. Here’s a proven, step-by-step process:

• Confirm the code using a professional-grade scan tool. Clear all codes and see if B1820 returns.
• Inspect the rear wiper relay and wiring harness visually for signs of damage, chafing, or corrosion—pay close attention to areas where the harness flexes or is exposed to moisture.
• Check the relay socket and connectors for signs of water intrusion, corrosion, or loose pins. Clean and repair as needed.
• Test the relay using a multimeter. Measure coil resistance and check for a short to battery voltage on the control circuit.
• Check the rear wiper motor for internal shorts by unplugging it and testing circuit continuity as per OEM specifications.
• Test for battery voltage where it shouldn’t be present (e.g., at the relay control side when the switch is off).
• If all else fails, consider a BCM fault. Check for BCM-related TSBs (Technical Service Bulletins) from the OEM before replacement.

Possible Repairs for B1820 (Linked to Causes) #

Once the root cause is found, repair should be both targeted and thorough. Here are the most common repair actions for each likely cause:

• Repair or replace damaged wiring harnesses (fix chafed or shorted wires, reseal with proper insulation, and secure the harness to prevent future damage)
• Replace the rear wiper up relay if testing confirms an internal short or coil failure
• Clean or replace corroded connectors and apply dielectric grease to prevent moisture ingress
• Replace the rear wiper motor if it’s internally shorted or draws excessive current
• Replace the BCM only after all other possibilities are ruled out and as per OEM diagnostic procedures

Is It Safe to Drive With Code B1820? #

Yes, but with limitations: Code B1820 does not directly affect vehicle drivability or safety systems like braking or steering. However, if you rely on your rear wiper for visibility—especially in rain, snow, or dusty conditions—address the problem as soon as possible. Reduced rearward visibility can be a safety hazard. If you’re in dry weather and don’t require the rear wiper, it’s generally safe to continue driving until repairs are scheduled.

Vehicles Most Commonly Affected by B1820 #

B1820 is most frequently observed in vehicles with advanced rear wiper circuitry and relay-controlled wiper motors. The following makes and models have documented occurrences:

• Ford Explorer, Escape, and Edge (2012–2022)
• Chevrolet Traverse, Equinox, and Tahoe (2010–2021)
• Toyota RAV4, Highlander, and Sienna (2010–2023)
• Nissan Rogue, Pathfinder, and Murano (2011–2022)
• Other SUVs and hatchbacks with powered rear wipers

Common Mistakes & Best Practices for B1820 #

Diagnosing electrical codes like B1820 can trip up even seasoned techs. Here are some pitfalls to avoid, and smart steps to ensure a lasting repair:

• Assuming the relay is always to blame—always test before replacing
• Overlooking corroded or water-damaged connectors, especially after leaks or car washes
• Skipping a thorough wiring inspection in favor of “easy” parts replacement
• Forgetting to clear the code after repair and verify system operation
• Not checking for related TSBs or OEM wiring diagram updates

Quick FAQ for Code B1820 #

Q: Will disconnecting the battery clear code B1820?
A: Disconnecting the battery may clear the code temporarily, but unless the root cause is repaired, the code will return as soon as the fault is detected again.

Q: Can a faulty rear wiper switch cause B1820?
A: While rare, a failed switch could cause improper voltage routing, but the majority of B1820 cases are due to wiring, relay, or motor issues.

Q: Do I need a scan tool to diagnose B1820?
A: A scan tool is essential for code confirmation and BCM data access, but electrical testing (with a multimeter) is also required to pinpoint the exact fault.