B1805 — Lamp Turn Signal Rear Output Circuit Short To Ground

B1805 — Lamp Turn Signal Rear Output Circuit Short To Ground. A fault in the body electrical system. The car is usually drivable while you plan the repair. Typical causes: faulty switch, motor or actuator of the affected system, damaged wiring in door jambs or wet areas, body control module (BCM) fault.

body electrical

Is it safe to drive?

Short-term driving is OK Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

How to diagnose with an OBD scanner

Read the code and freeze frame Connect an OBD2 scanner, confirm B1805 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 body electrical system for damage, corrosion, chafing or poor contact.
Subsystem check Operate the affected function while watching its switch and motor PIDs in live data.
Subsystem check Inspect connectors and wiring at flex points (door jambs, tailgate hinges) — wires break there first.
Verify the repair Clear the code, complete a full drive cycle including the conditions from the freeze frame, and confirm B1805 does not return.

Approximate repair cost

Repair cost depends on which component actually failed. Typical scenarios for B1805 (parts and labor, USD, independent shop rates): Replace the switch or actuator: $120–$450; BCM repair or replacement: $300–$900; Repair wiring or connectors: $80–$250. Overall, fixing B1805 usually costs between $80 and $900. An accurate diagnosis before buying parts saves money — the most expensive scenario is rarely the first one to check.

Common questions

Is it safe to drive with B1805?

Usually safe to drive — body codes rarely affect drivability. Exceptions: exterior lighting and wipers in bad weather, and central locking faults that can leave the car unsecured.

What is the most common cause of B1805?

The most common causes are: faulty switch, motor or actuator of the affected system, damaged wiring in door jambs or wet areas, body control module (BCM) fault.

How much does it cost to fix B1805?

Replace the switch or actuator — $120–$450; BCM repair or replacement — $300–$900; Repair wiring or connectors — $80–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

Will B1805 clear itself?

Sometimes B1805 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

How do I diagnose B1805 myself?

Start with a scan: confirm B1805, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the body electrical system, and verify the suspect component against live data before buying parts.

Modern vehicles rely on the body control module to manage exterior lighting, including the rear turn signals. When the BCM detects that the rear turn signal output circuit is drawing excessive current due to a short to ground, it sets fault code B1805. This diagnostic trouble code belongs entirely to the body electrical category within the OBD2 standard and does not affect engine management systems directly.

The BCM constantly monitors the resistance and current flow in all lighting circuits while the vehicle is running. When a short to ground causes readings to stray outside the expected parameters for a predetermined number of drive cycles, the module logs B1805 and triggers the check-engine or body-system warning light. The freeze frame data stored alongside the code captures the exact operating conditions — engine speed, load, coolant temperature, and vehicle speed — at the moment the fault first appeared. This snapshot gives technicians a precise starting point for diagnosis and helps confirm whether the issue is intermittent or persistent.

The rear turn signal circuit runs from the BCM through the door jamb wiring harness to the rear lamp assembly. Repeated opening and closing stresses these wires at flex points, making them vulnerable to insulation damage and short circuits. Understanding this architecture explains why B1805 often reappears after simple fixes if the underlying wire damage is not properly addressed.

Common Symptoms of B1805

Rear turn signals fail to activate on the affected side or both sides intermittently
Hazard flashers may also be inoperative depending on vehicle architecture
Dashboard warning light illuminates indicating a body electrical fault
Other body functions such as power door locks or interior lighting operate normally in most cases
The malfunction may disappear temporarily after wiggling the steering column or rear lamp connector

What Triggers B1805

Damaged wiring insulation in door jambs or trunk areas where wires bend repeatedly
Corrosion buildup at electrical connectors from moisture intrusion
Failed turn signal switch or multifunction stalk assembly
Blown fuse or faulty relay supplying the turn signal circuit
Short circuit inside the rear lamp housing affecting the turn signal filament
Body control module internal failure producing incorrect output signals

Diagnosing B1805

Connect an OBD2 scanner, retrieve stored codes, and record the freeze frame data associated with B1805 — this records the driving conditions when the fault first occurred.
Check for related diagnostic trouble codes in the body module — coexisting codes often point to the root cause rather than the symptom.
Search the manufacturer database for technical service bulletins specific to your vehicle make and model — many B0xxx code patterns have documented factory fixes or software recalibrations available.
Perform a thorough visual inspection of the turn signal circuit wiring, focusing on the door jamb transition points and rear lamp connectors for cracked insulation, bent pins, or greenish corrosion deposits.
Operate the turn signal lever while observing live data on the scanner to see whether the BCM output signal toggles correctly even though the bulbs do not illuminate.
Clear B1805 after visual inspection, complete a full drive cycle including conditions matching the freeze frame, and verify the code does not return before considering the repair complete.

Repair Options and Costs

The most cost-effective approach addresses simple failures before pursuing expensive component replacement:

Repair damaged wiring or replace corroded connectors: $80–$250
Replace faulty turn signal switch or actuator: $120–$450
Repair or replace the body control module: $300–$900

Labor rates at independent shops typically run $75–$125 per hour. Wiring repairs in the door jamb usually require 1–2 hours of labor, while BCM replacement often demands 2–4 hours depending on vehicle accessibility.

Total repair costs for B1805 typically fall between $80 and $900 depending on which component is actually faulty. An accurate diagnosis before purchasing parts prevents unnecessary spending — the BCM replacement scenario represents the maximum expense and should be considered only after wiring and switches have been ruled out.

Driving Safety with B1805

B1805 does not impair engine performance or transmission function, making it generally safe to operate the vehicle short distances. However, non-functional rear turn signals significantly reduce visibility to other drivers, increasing collision risk especially in low-light conditions, heavy rain, or fog. Driving with this fault present is not recommended for extended periods or on busy highways. Address the underlying cause promptly to restore full signaling capability and maintain road safety.