B1805 — Lamp Turn Signal Rear Output Circuit Short To Ground #

Note: The description of this Diagnostic Trouble Code (DTC) may vary depending on the vehicle manufacturer. Always consult your vehicle’s repair manual or OEM (Original Equipment Manufacturer) documentation for the exact definition.

• B1805: Rear Turn Signal Lamp Output Circuit Short to Ground (Ford, Toyota)
• B1805: Rear Turn Signal Lamp Circuit Low (Mazda)
• B1805: Rear Turn Signal Lamp Shorted to Ground (Hyundai, Kia)

Summary of Code B1805 #

The B1805 code indicates that the vehicle’s onboard diagnostics (OBD-II/EOBD) system has detected a short-to-ground condition in the rear turn signal lamp output circuit. In simple terms, this means that the wire or component responsible for powering the rear turn signal (the blinker at the back of your vehicle) is unintentionally making contact with the vehicle’s ground (chassis), causing abnormal operation. This issue can result in rear turn signals that do not function correctly or at all, which is a safety concern. The code is set by the Body Control Module (BCM) or a similar controller when it senses voltage below the expected range in the circuit. Addressing this issue promptly helps maintain safe signaling and prevents possible electrical damage.

Frequent Symptoms for Code B1805 #

When the B1805 code is active, you may notice several warning signs. These symptoms often appear suddenly and can affect your ability to communicate your driving intentions to other road users. Common indicators include:

• Rear turn signal not working (one or both sides)
• Turn signal indicator blinking faster or not at all on the dashboard
• Other exterior lights behaving erratically (if circuits are shared)
• Warning light or message on the instrument panel (such as “Check Turn Signal” or a generic warning symbol)
• Possible blown fuse related to lighting circuits

Probable Causes for Code B1805 #

The most frequent causes of a B1805 DTC relate to wiring or component faults. The following list is ordered from most to least common based on technician experience and OEM data:

1. Damaged or frayed wiring in the rear turn signal circuit (most commonly where the harness flexes or is exposed to moisture)
2. Corroded or shorted rear turn signal bulb socket due to water ingress or debris
3. Faulty rear turn signal bulb causing internal short
4. Incorrectly installed or aftermarket bulbs that do not match OEM specifications
5. Defective Body Control Module (BCM) or related relay (rare, but possible)

Step-by-Step Diagnostic for Code B1805 #

Diagnosing a B1805 trouble code involves methodically checking the circuit for shorts and component failures. Here is a clear step-by-step process:

• Verify the code using a reliable OBD-II scan tool, and check for any related codes that might indicate systemic issues.
• Inspect the rear turn signal bulb(s) for proper type, condition, and signs of internal failure (burn marks, broken filament).
• Examine the bulb socket for corrosion, water intrusion, or bent pins that could cause a short to ground.
• Check the wiring harness from the BCM to the rear lamp for any visible damage, rubbing, or pinched sections, especially around trunk hinges or tailgate areas.
• Test circuit continuity using a multimeter, ensuring there is no continuity between the signal wire and ground when the bulb is removed.
• Test BCM output if all physical components are intact, as a failed output driver could also trigger this code.

Possible Repairs for Code B1805 #

The necessary repairs for a B1805 code depend on the root cause identified during diagnostics. Common solutions include:

• Repair or replace damaged wiring—Insulate or replace any frayed wires in the turn signal circuit.
• Clean or replace bulb sockets—Remove corrosion, dry out any moisture, or fit a new socket if contacts are damaged.
• Install the correct bulb—Ensure the installed bulb matches OEM specifications in type and wattage.
• Replace faulty bulbs—Install new bulbs if shorts are found inside the old ones.
• Replace the BCM or relay—If BCM output is not functioning and all other components check out, a replacement may be required (rare).

Is It Safe to Drive With Code B1805? #

Limited — Caution Advised. While the vehicle can often be driven with a B1805 code, your rear turn signal may not function, which is a safety hazard and could result in a traffic citation. Turn signals are essential for communicating lane changes and turns to other drivers. It is best to repair the issue as soon as possible and avoid driving at night or in heavy traffic until fixed.

Vehicles Most Commonly Affected by Code B1805 #

While B1805 can appear on many modern vehicles equipped with OBD-II and advanced lighting control, it is most often reported on the following makes and models:

• Ford Focus, Escape, and F-150 (2010–2020)
• Toyota Corolla, Camry, and RAV4 (2012–2018)
• Hyundai Elantra and Sonata (2011–2019)
• Kia Forte and Optima (2011–2019)
• Mazda 3 and 6 (2013–2018)

Common Mistakes & Best Practices for Code B1805 #

Diagnosing and fixing a B1805 code requires attention to detail. Many DIYers and even some professionals make avoidable errors. Here’s what to watch out for:

• Ignoring possible water intrusion in the rear lamp housing or trunk area
• Replacing the bulb without checking socket or wiring condition
• Using incorrect bulb types or wattage
• Overlooking harness damage at trunk/tailgate hinges
• Clearing the code without addressing the underlying issue—code will typically return

Quick FAQ for Code B1805 #

Have more questions about B1805? Here are some rapid answers:

• Q: Will B1805 make my car fail inspection?
  A: In most states, a non-functioning turn signal will cause your vehicle to fail a safety inspection.
• Q: Can a blown fuse alone cause B1805?
  A: Yes, but a blown fuse is usually a symptom of an underlying short—simply replacing the fuse may not resolve the root problem.