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

body electrical

Is it safe to drive?

Drive with caution Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1820 is stored, and save the freeze frame data — it shows engine conditions when the fault was detected.
Check for companion codes and TSBs Related codes often reveal the real root cause. Also check manufacturer technical service bulletins (TSB) for your make and model — many B0xxx issues have factory fixes or software updates. Search by VIN on the manufacturer site or nhtsa.gov.
Inspect wiring and connectors Visually inspect the wiring harness and connectors related to the ignition system for damage, corrosion, chafing or poor contact.
Subsystem check Swap the coil to another cylinder and see if the fault code follows it.
Subsystem check Inspect spark plugs for wear, oil or carbon tracks and check plug gaps.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1820 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1820 (parts and labor, USD, independent shop rates): Replace spark plugs: $90–$250; Repair coil wiring or connector: $80–$250; Replace an ignition coil: $150–$380. Overall, fixing B1820 usually costs between $80 and $380. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

How do I diagnose B1820 myself?

Start with a scan: confirm B1820, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition system, and verify the suspect component against live data before buying parts.

How much does it cost to fix B1820?

Replace spark plugs — $90–$250; Repair coil wiring or connector — $80–$250; Replace an ignition coil — $150–$380. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Is it safe to drive with B1820?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What are the symptoms of B1820?

Drivers most often notice: misfires under load or at idle, increased fuel consumption, Check Engine Light on, hard starting, especially in damp weather.

What does OBD2 code B1820 mean?

Wiper Rear Motor Up Relay Coil Circuit Short To Battery (B1820): a body electrical fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by failed ignition coil or coil pack, worn spark plugs or wrong plug gap, faulty ignition control circuit in the ECM.

When your vehicle's onboard computer detects a continuous short-to-battery condition in the rear wiper motor's up relay coil circuit, it stores trouble code B1820. This fault falls squarely in the body electrical category, meaning the problem lives in the secondary electrical systems that handle comfort and convenience features rather than the engine's core operation. Unlike codes that trigger on a single bad reading, the module requires the abnormal condition to persist across multiple drive cycles before illuminating the check engine light and recording the failure. When B1820 is set, the freeze frame data captured alongside it provides a snapshot of engine load, RPM, coolant temperature, and vehicle speed at the exact moment the fault occurred—information that proves invaluable when you need to reproduce the failure condition during diagnosis.

The rear wiper motor assembly relies on a relay to engage the motor when you activate the switch. That relay contains an electromagnetic coil, and B1820 specifically indicates the control circuit feeding that coil is experiencing an unwanted direct connection to battery voltage. When this short exists, the relay may energize at inappropriate times, fail to disengage properly, or not receive the signal to activate at all. The powertrain control module monitors voltage conditions in this circuit and flags B1820 when readings deviate from factory specifications by a margin significant enough to indicate a genuine fault rather than normal electrical noise.

Drivers typically notice the rear wiper behaving erratically or not operating at all when B1820 is active. The most obvious symptom involves the rear wiper failing to respond when activated, or conversely, continuing to run after the driver has turned it off. Some vehicles may also display related warning indicators on the instrument cluster, depending on how the manufacturer programmed the body control module's fault response. In intermittent cases, the wiper might function normally most of the time but stutter, hesitate, or exhibit delayed response when conditions trigger the fault.

Common Symptoms of B1820

Rear wiper fails to activate when the switch is engaged
Wiper motor runs continuously without responding to the off command
Intermittent operation where the wiper works sometimes but not others
Wiper moves sluggishly or stalls during the wiping cycle
Check engine or body control warning light illuminated on the dashboard
Unusual clicking sounds from the rear wiper motor area when the system is powered

Moisture intrusion ranks as the leading cause of B1820. Water finds its way into the rear wiper motor housing, the wiring connector, or the harness routing through the hatch or tailgate. Corrosion develops on terminals and pins, creating resist ance or partial short circuits that the module interprets as the battery short condition. Beyond moisture, damaged wiring insulation in the wiper circuit commonly triggers this code. The harness flexes every time the hatch opens and closes, and over time the insulation cracks, exposing bare wire to the metal body and shorting the circuit. A faulty relay coil itself can also produce these symptoms if the internal windings short internally. Finally, a defective body control module that misinterprets valid signals as faults remains a possibility, though this accounts for a small percentage of cases.

Common Causes of B1820

Water or moisture infiltration into the rear wiper motor or connector housing
Corrosion on electrical terminals within the wiper circuit harness
Chafed, melted, or cut wiring insulation in the rear wiper motor circuit
Failed wiper motor relay with an internally shorted coil winding
Poor electrical connections at the wiper motor connector due to loose pins or damaged seals
Defective body control module processing incorrect voltage readings

How to Diagnose B1820

Begin by connecting an OBD2 scanner to confirm B1820 is stored and record all available freeze frame data. This snapshot tells you the exact circumstances present when the module first detected the fault, allowing you to simulate those conditions during testing. Next, perform a thorough visual inspection of the rear wiper motor, its relay if externally mounted, and the complete wiring harness between the motor and body control module. Look specifically for cracked insulation, corroded terminals, and any signs of water entry into connectors. Check that the connector seals are intact and that no moisture residue exists in the motor housing.

Using a multimeter, test for unwanted continuity between the relay coil control circuit and battery power at various points in the harness. A reading of near-zero ohms between these circuits confirms the short that sets B1820. If the wiring checks out, swap the suspected relay with a known-good unit from the same vehicle or a compatible part from the parts shelf—many relays are universal and can be tested in other circuits. Finally, clear the code and operate the wiper system through multiple complete cycles, paying special attention to any condition that previously triggered the fault. If B1820 does not return after thorough testing, the issue was likely a connection problem that improved when you disturbed the harness during inspection.

Repair Options with Pricing

Depending on what your diagnosis reveals, repair costs for B1820 vary significantly. If moisture is the culprit, cleaning corrosion from terminals and applying dielectric grease typically runs between $80 and $250 when performed at a shop. Wiring repairs for damaged harness sections average $80 to $250 depending on whether the affected section can be spliced or requires full harness replacement. Replacing a faulty wiper motor relay costs approximately $80 to $200 for parts alone, with labor adding $50 to $100 at independent shop rates. In the worst-case scenario involving replacement of the rear wiper motor assembly and associated wiring, total costs can reach $150 to $380.

Can You Drive with B1820?

Proceed with caution. While B1820 does not directly affect engine operation or safe handling characteristics, the underlying electrical fault could worsen over time. A persistent short can drain the battery, cause unexpected fuse failures, or in rare cases create a fire hazard if left unaddressed. If the rear wiper system shares fuses or circuits with other critical safety features on your vehicle, the malfunction could potentially interfere with those systems. Address this code within a reasonable timeframe to avoid being stranded by a dead battery or facing more expensive repairs down the road.