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

The diagnostic trouble code B1820 indicates an electrical issue within the rear wiper motor up relay circuit, specifically a short to the battery. This means the vehicle’s electronic control unit (ECU) detects that the relay’s coil circuit is unexpectedly grounded or connected directly across the battery voltage, which can cause electrical problems or component damage.

Note that labels and terminology for this code can vary depending on the vehicle manufacturer. Different OEMs may assign alternate codes or descriptions, but the core issue remains similar. Below is a concise overview of Fast Facts related to this trouble code.

Fast Facts

System affected: Rear wiper motor circuit
Severity: Moderate — potential electrical damage if not addressed promptly
Main symptoms: Rear wiper malfunction, relay clicking, warning lights
Driveability: No — this code typically affects comfort features rather than core drivability

Manufacturer variations for trouble code B1820

The code B1820 might not be universally used across all vehicle brands. Instead, each manufacturer often assigns triangle-specific labels or code descriptions that align with their diagnostic standards. Here are some known variations:

Ford: B1820 — Wiper Motor Up Relay Coil Circuit Short to Battery
Volkswagen Group (VW, Audi, SEAT, Škoda): 5DF — Wiper Rear Motor Relay Short to Battery
Honda: P2611 — Wiper Motor Circuit Malfunction (though specific code may vary)
Mercedes-Benz: 2083 — Rear Wiper Control Circuit Fault

It is important to consult the specific vehicle’s service manual or official OEM diagnostic codes for the exact label, as variations are common depending on the brand and model.

What does trouble code B1820 mean?

B1820 indicates that the vehicle’s ECUrelay coil circuit responsible for controlling the rear wiper motor’s up function. Specifically, the problem is a short to the battery, meaning that the relay coil’s circuit is incorrectly connected directly to the battery voltage, bypassing normal control signals.

The ECU constantly monitors the electrical circuit for anomalies. If it detects a short circuit—a direct connection causing excessive current flow—it triggers this specific diagnostic trouble code (DTC). It is often a safety feature to prevent damage to electrical components and wiring.

This code most frequently appears in situations where an electrical issue develops, perhaps after recent repairs, modifications, or due to wiring deterioration.

Severity and risks of trouble code B1820

The severity of B1820 should not be underestimated. A short circuit to the battery in the relay coil circuit can lead to several risks, including:

Electrical damage to wiring or the relay itself if not resolved promptly
Blown fuse in the circuit, leading to loss of function for related systems
Potential damage to the vehicle’s electrical system over time if the short persists
Malfunction of rear wiper, affecting visibility and vehicle aesthetics in adverse weather conditions

In most cases, safe to drive temporarily with this code, but repeated electrical issues or non-resolving faults can threaten the overall electrical stability of the vehicle. It is recommended to address the issue as soon as possible.

Symptoms of trouble code B1820

The appearance of B1820 often coincides with specific symptoms, although some vehicles may show no apparent signs. Common symptoms include:

Rear wiper malfunction: it may not operate at all or behave intermittently
Relays clicking: audible clicking from the rear wiper relay when the vehicle is turned on
Warning lights: an electrical warning or warning light related to the wiper system or general body control
Electrical fuse blowout: replacing a fuse related to the rear wiper circuit may be necessary
Unusual electrical behaviour: such as flickering or irregular operation of related components

Most likely causes of trouble code B1820

Understanding the root causes of this code helps narrow down inspection and repairs. The causes are typically related to wiring or relay issues. Here are the most common causes, ranked from most to least probable:

Shorted relay coil wiring: a direct short circuit within the relay’s wiring harness due to wear, damage, or improper modification.
Faulty relay: a relay that has internally shorted or become defective, causing a persistent short to voltage.

Note: This is usually replaceable and often the most straightforward cause to confirm.

Damaged wiring or connectors: corrosion, abrasion, or damaged insulation in the wiring connected to the relay coil circuit.
Misconfigured or malfunctioning control module: rare, but possible if the ECU is sending incorrect signals or has internal faults.
Power supply issues: such as a wiring short elsewhere in the circuit affecting the relay circuit indirectly.

How to diagnose trouble code B1820

Diagnosing this fault involves a systematic approach to verify electrical integrity and ensure communication between components. Here are generic diagnostic steps:

Visual inspection: Examine wiring harnesses, connectors, and relays related to the rear wiper circuit for signs of damage, corrosion, or loose connections.
Check fuse integrity: Inspect all relevant fuses—replace if blown—and confirm the fuse rating matches OEM specifications.
Test relay operation: Using a relay tester or multimeter, verify the relay functions correctly and is not internally shorted.
Conduct continuity tests: Check wiring continuity from the relay coil circuit to the ECU and battery to identify short circuits or open circuits.
Live data reading: Connect a diagnostic scan tool to monitor the circuit voltages and relay activation signals.
Check for short to battery: Carefully inspect wiring for accidental grounding or wiring damage that might cause a short.
ECU reference check: Confirm the control module is functioning properly and not providing false signals or commands.

Possible repairs for trouble code B1820

Addressing B1820 typically involves pinpointed repairs depending on the identified cause. Here are common solutions, each suited to specific issues:

Replace faulty relay: if the relay itself is defective, replace it. This is a straightforward, often basic repair requiring minimal tools.
Repair or replace damaged wiring or connectors: repair involves soldering, splicing, or replacing wiring harness segments—a task generally best handled by professionals.
Remove wiring shorts: identify the short circuit causing the coil to ground or connect directly to the battery and correct the wiring routing or insulation.
ECU reprogramming or replacement: in rare cases, if the control module is at fault, a professional diagnosis and possible reprogramming or replacement may be necessary.
Fuse replacement: if a blown fuse is identified, replace with correct rating and investigate underlying cause to prevent recurrence.

Vehicles commonly associated with trouble code B1820 in Europe

This code is seen in various passenger vehicles. While data is limited to general trends, the following brands frequently report rear wiper circuit issues in Europe:

Volkswagen Group: VW Golf, Skoda Octavia, Audi A3, Seat Leon
Ford: Focus, Fiesta, Mondeo
BMW: 1 Series, 3 Series
Peugeot: 308, 3008

The specific engine types or family are less pertinent here, as this issue generally relates to wiring and relay circuits rather than engine design.

Frequent mistakes with trouble code B1820

Diagnosing and repairing B1820 requires caution to avoid additional issues. Common errors include:

Ignoring visible wiring damage: failing to thoroughly inspect wiring or connectors often leads to unresolved faults.
Replacing relay without testing: replacing components blindly may not address the root cause if wiring shorts or ECUs are at fault.
Overlooking fuse issues: often, a blown fuse is an easy fix, but the underlying cause must be determined to prevent future failures.
Using incompatible replacement parts: always verify that new relays and wiring replacements match OEM specifications.
Skipping diagnostic data verification: relying solely on the code without live measurement can lead to incomplete repairs.

FAQ — trouble code B1820

Can this code disappear on its own?

Typically, no. Since B1820 indicates a hardware fault such as a short circuit, it generally persists until repairs are made. Clearing the code may temporarily reset the warning, but the root cause must be addressed to prevent reappearance.

Can I keep driving?

While it is usually safe to drive temporarily, especially if the rear wiper is not needed, persistent electrical faults can cause damage over time. It’s best to diagnose and repair the issue promptly to avoid further electrical complications.

Why does the code return after clearing it?

The underlying cause—such as a shorted relay wire or damaged wiring—remains unaddressed. Clearing the code only resets the ECU’s warning; it will re-detect the fault once the vehicle’s electrical system is active again.