B1802 — Lamp Turn Signal Rear Output Circuit Failure

What does OBD2 code B1802 mean?

Lamp Turn Signal Rear Output Circuit Failure (B1802): a body electrical fault affecting the body electrical system. The car is usually drivable while you plan the repair. Most often caused by blown fuse or failed relay, body control module (BCM) fault, corroded or loose connectors.

How much does it cost to fix B1802?

BCM repair or replacement — $300–$900; Replace the switch or actuator — $120–$450; 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.

How do I diagnose B1802 myself?

Start with a scan: confirm B1802, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the lamp turn signal rear output circuit, and verify the suspect component against live data before buying parts.

Is it safe to drive with B1802?

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.

Will B1802 clear itself?

Sometimes B1802 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.

When your vehicle's computer logs trouble code B1802, it's telling you that a specific problem exists in the rear turn signal circuit on one side of the car. This is a body electrical fault, not an engine or drivetrain issue. The body control module (BCM) monitors the output signal feeding the rear turn signal lamp, and when it detects that the circuit isn't behaving as it should—either drawing too much current, too little, or no current at all—it sets B1802 and illuminates the appropriate warning light on your dashboard.

The module doesn't throw this code based on a single bad reading. Automotive computers are designed to confirm problems before flagging them, so B1802 gets stored only after repeated verification cycles under specific conditions. When the code was triggered, the ECU captured a freeze frame snapshot showing engine load, RPM, coolant temperature, and vehicle speed at that exact moment. This data is gold when you're trying to reproduce the fault during diagnosis—you need to recreate those same conditions to see the problem firsthand.

Behind B1802 is a specific failure in the body electrical system: lamp turn signal rear output circuit failure. The onboard computer stores it in the body electrical group after verifying the fault over repeated checks.

What are the symptoms of B1802?

The most obvious sign is a dashboard warning light related to the turn signal or exterior lighting system. Beyond that, you may notice one or more of the following:

• The affected rear turn signal fails to illuminate when activated, or flashes erratically
• The turn signal works intermittently, especially during temperature swings or wet weather
• Other body functions on the same circuit—interior lighting, tail lights—may behave abnormally
• The turn signal indicator on the dashboard may flash faster than normal (hyperflashing)
• No change to engine performance, fuel economy, or throttle response
• The code may clear temporarily after a reset, then return under the same conditions

What causes B1802?

Several failure modes can trigger this code. Most likely causes first:

• Corroded or moisture-damaged connector at the rear turn signal housing or tail light assembly
• Burned-out turn signal bulb (though this usually triggers a different code, some vehicles set B1802 first)
• Chafed or broken wiring at the tailgate hinge or door jamb where wires flex repeatedly
• Blown fuse protecting the turn signal circuit (check the instrument panel or body fuse box)
• Failed turn signal switch or column stalk
• Faulty body control module output stage (less common but possible on high-mileage vehicles)
• Poor ground connection for the rear turn signal circuit

How to diagnose B1802

Follow a logical troubleshooting sequence to pinpoint the exact cause without replacing parts unnecessarily.

1. Connect an OBD2 scanner and confirm the code — Read B1802 along with any other stored codes and record the freeze frame data. This tells you what conditions were present when the module detected the fault.

2. Check manufacturer TSBs for your specific vehicle — Search the National Highway Traffic Safety Administration website or your manufacturer's technical service bulletins using your VIN. Some B0xxx-series codes have documented factory fixes or software updates.

3. Visually inspect the rear turn signal connectors and wiring — Remove the tail light assembly and examine the socket, connector pins, and wiring for corrosion, bent pins, or pushed-out terminals. Moisture intrusion is the most common culprit here.

4. Test for power and ground at the turn signal circuit — Use a multimeter or test light to verify that voltage is present at the socket when the turn signal is activated, and that ground is solid. No voltage points to an upstream wiring or BCM issue; no ground points to a grounding problem.

5. Operate the turn signal and monitor live data — With a scanner capable of reading body module data, watch the turn signal switch state and output command while activating the signal. This tells you whether the BCM is correctly sending the command.

6. Clear the code and perform a drive cycle — Reset the code, then drive the vehicle including maneuvers that trigger the rear turn signals. If B1802 returns, you have confirmed an active fault rather than an intermittent glitch.

Repair options and costs for B1802

Once you've isolated the failure point, here are typical repair scenarios with parts and labor:

• BCM repair or replacement — $300–$900. In rare cases where the module's output transistor has failed internally, BCM replacement is necessary. Many shops recommend a remanufactured unit over new for cost savings.
• Replace the switch or actuator — $120–$450. If the turn signal stalk or column switch has failed, parts and installation are straightforward on most vehicles.
• Repair wiring or connectors — $80–$250. Cleaning corroded connectors, soldering broken wires at flex points, or replacing a damaged harness section falls in this range. Connector replacement with OE-style weatherpack terminals is often the most durable fix.

How much does it cost to fix B1802?

Total cost to resolve B1802 depends entirely on which component is actually at fault. The $80–$250 wiring repair is by far the most common solution. BCM replacement is the least likely and most expensive scenario. Always spend time on accurate diagnosis before purchasing any parts—an ounce of testing prevents wasting hundreds of dollars on a guess.

Can you drive with B1802?

Yes, in most cases B1802 does not affect your ability to drive. This code lives in the body electrical group, so engine operation, transmission function, and safety systems remain unaffected. The practical concern is visibility: if your rear turn signal isn't working, other drivers may not see your turning intentions, especially at night or in rain. Repair the fault before extended highway driving or in conditions where signaling matters most.

Related OBD2 codes

• B1800: Lamp Turn Signal Front Output Circuit Short To Battery
• B1801: Lamp Turn Signal Front Output Circuit Short To Ground
• B1803: Lamp Turn Signal Rear Output Circuit Open
• B1804: Lamp Turn Signal Rear Output Circuit Short To Battery
• B1805: Lamp Turn Signal Rear Output Circuit Short To Ground
• B1806: Lamp Tail Output Circuit Failure