B16A4 – Right turn signal bulb outage (Mitsubishi)

Mitsubishi-specific code — factory diagnostic data

Last updated: March 29, 2026

Definition source: Mitsubishi factory description · Autel MaxiSys Ultra & EV. Diagnostic guidance is based on factory-defined fault logic for this code.

B16A4 means your 2016 Mitsubishi Outlander thinks the right turn signal bulb is out. The real-world effect is a right blinker that does not light, blinks fast, or works only sometimes. According to Mitsubishi factory diagnostic data, this manufacturer-specific body code indicates a right turn signal bulb outage. That description points you toward the right-side turn signal lamp circuit as a suspected trouble area. It does not confirm a bad bulb. You must verify the lamp, socket, wiring, and module output before you replace parts.

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B16A4 Quick Answer

B16A4 on a Mitsubishi Outlander sets when the body system detects an “outage” condition on the right turn signal bulb circuit. Confirm the bulb actually illuminates and then test the right turn signal feed and ground under load.

What Does B16A4 Mean?

Official definition: “Right turn signal bulb outage.” In plain terms, the vehicle detected that the right turn signal lamp did not draw the expected current or did not respond as expected when commanded on. In practice, that usually shows up as a right turn signal that fails, flickers, or causes fast-flash on the indicator.

What the module checks and why it matters: The body system that controls exterior lighting monitors the right turn signal circuit while it commands the lamp. It looks for an electrical response that matches a working bulb and wiring. An open circuit, high resistance, short, wrong bulb type, or poor ground can all look like an “outage.” Use the code as a direction to test the circuit, not as proof that a bulb failed.

Theory of Operation

Under normal operation, the Mitsubishi body lighting controller switches power to the right turn signal lamp and expects the circuit current to match a working load. The instrument cluster then flashes the right indicator based on that command and status.

This code sets when the controller commands the right turn signal on but sees an abnormal electrical signature. An open filament, loose socket tension, corrosion, or damaged wiring changes current flow. A short to ground or short to power can also disrupt the expected response. The module flags the condition as a bulb outage to protect the circuit and alert the driver.

Symptoms

You will usually notice a right turn signal problem first, then find B16A4 stored in body-related diagnostics.

• Right blinker inoperative at the affected lamp location
• Fast flash on the cluster right turn indicator
• Intermittent operation that changes with bumps or moisture
• Dim right turn signal compared to the left side
• Bulb warning message or exterior lamp warning (if equipped)
• Hazard lamp asymmetry where the right side does not match the left
• Stored body DTC B16A4 after repeated right turn signal use

Common Causes

• Failed right turn signal bulb or LED assembly: An open filament or failed LED driver stops current flow, so the Mitsubishi body control logic flags an outage.
• High-resistance bulb socket contacts: Heat, looseness, or light corrosion increases resistance and drops current below the module’s expected load range.
• Water intrusion in the right lamp housing: Moisture attacks terminals and creates intermittent opens or shorts that look like a bulb outage to the module.
• Open circuit in the right turn signal feed wire: A break in the power side prevents the lamp from drawing current when the turn signal output commands ON.
• High resistance or open in the right lamp ground path: A weak ground limits lamp current, and the module interprets the low load as an inoperative bulb.
• Connector pin fit issues at the right rear lamp or front lamp: Spread terminals or partially seated connectors create intermittent contact and set the code during vibration.
• Short to ground on the turn signal output circuit: A chafed wire can pull the output low, causing the driver to protect itself and the lamp to stay off.
• Incorrect bulb type or aftermarket LED conversion without load management: A low-current LED “bulb” can trigger an outage decision because the load does not match the Mitsubishi calibration.
• Body control module (ETACS/BCM) output driver fault: A weakened driver can command the circuit but fail to source current, which mimics an external outage.

Diagnosis Steps

Use a scan tool that can access Mitsubishi body data and run an output test. Have a digital multimeter and a test light that can load the circuit. Back-probe pins and use a bulb-type load when possible. Keep wiring diagrams handy, because Mitsubishi lamp routing varies by platform and trim.

1. Confirm DTC B16A4 and check if it shows as pending or stored. Record freeze frame data if available, focusing on battery voltage, ignition state, and turn signal switch status. Note any companion body codes for exterior lighting, voltage supply, or lamp monitoring.
2. Inspect the right turn signal lamp operation at all locations that apply on this Outlander. Check front, rear, and mirror repeater if equipped. Also perform a quick visual check of the full circuit path, including obvious harness rub points and recent repair areas, before meter work.
3. Check all related fuses and power distribution for exterior lighting and the ETACS/BCM. Verify each fuse with a loaded test, not continuity alone. A fuse can pass continuity and still fail under load at the blades or in the fuse box.
4. Verify ETACS/BCM power and ground integrity under load. Command the right turn signal ON and voltage-drop test the module grounds while the circuit operates. Keep ground drop under 0.1V with the output active, or repair the ground path before chasing lamp wiring.
5. Inspect the right turn signal bulb, socket, and lamp connector. Look for heat damage, green corrosion, loose pins, and signs of water intrusion. Confirm the connector fully locks and the terminals grip the mating pins tightly.
6. Use the scan tool to run an active test or output control for the right turn signal. Watch the lamp and listen for relay clicks if the system uses one on this platform. Remember the difference between freeze frame and a snapshot: freeze frame shows conditions when B16A4 set, while a snapshot captures live data you trigger during wiggle testing.
7. Check the circuit at the lamp connector with the output commanded ON. Measure for battery voltage on the feed side while the lamp should illuminate. If voltage appears with no load but collapses with a test light or known-good bulb load, you have high resistance in the feed.
8. Prove the ground side at the lamp under load. Connect a test light from battery positive to the lamp ground terminal and command the turn signal ON. If the test light stays dim or flickers during wiggle testing, repair the ground, ground splice, or body attachment.
9. If the lamp does not receive power, isolate the open or high-resistance section. Work upstream from the lamp connector toward intermediate connectors and the ETACS/BCM output. Use voltage-drop tests across each connector while the circuit is commanded ON, because a connector can fail without looking damaged.
10. If you suspect a short to ground, disconnect the lamp and command the output. Check whether the output recovers and whether the code resets immediately. Inspect harness sections near the rear liftgate hinge area, bumper edges, and any clip points that can pinch wiring.
11. Address bulb type concerns last, but do not ignore them. If the vehicle has aftermarket LED “bulbs,” reinstall the correct type or a known-good OE-style load and retest. Load monitoring often triggers B16A4 even when the lamp appears to flash.
12. Clear codes and confirm the repair. Cycle ignition and operate the right turn signal for several minutes, including hazard operation. Recheck for pending and stored faults, because some body faults return immediately on key-on when the module sees a hard circuit problem.

Professional tip: Don’t trust a perfect 12V reading at the lamp with the bulb removed. A corroded feed can show full voltage with no current flow. Load the circuit with a test light or a known-good bulb, then repeat voltage-drop checks across the fuse box, connectors, and grounds to pinpoint the exact restriction.

Possible Fixes

• Replace the failed right turn signal bulb or lamp unit: Install the correct Mitsubishi-specified type only after you confirm proper power and ground at the connector.
• Repair socket or terminal tension issues: Clean light corrosion, restore terminal grip, and replace heat-damaged pigtails when the connector no longer holds pins securely.
• Repair power feed open or high resistance: Fix broken wires, damaged splices, or fuse box terminal problems verified by voltage-drop testing under load.
• Repair ground circuit faults: Clean and tighten body grounds, repair ground splices, and correct high voltage-drop points found with the lamp operating.
• Correct water intrusion source: Reseal the lamp housing, replace missing gaskets, and repair corroded terminals after you stop the leak.
• Remove incorrect LED conversions or add proper load management: Return to OE load or use an approved solution only after you verify the rest of the circuit works correctly.
• Repair ETACS/BCM output concerns after circuit proof: Consider module or driver diagnosis only when the lamp circuit tests good and the output fails under a verified load.

Can I Still Drive With B16A4?

You can usually drive a 2016 Mitsubishi Outlander with B16A4, but you should treat it as a safety issue in traffic. This manufacturer-specific code points to a right turn signal bulb outage. Other drivers may not see your intent to turn or change lanes. Use hand signals if you must drive before repairs. Avoid night driving and heavy traffic until you restore the right signal operation. If the cluster shows fast turn-signal flash, do not ignore it. That flash rate often confirms the vehicle detects low lamp current on the right side.

How Serious Is This Code?

B16A4 ranges from inconvenience to a real safety concern. It does not affect engine operation or braking. It can still cause a crash risk if other drivers cannot predict your next move. The problem becomes more serious when the right rear lamp is out. Rear signaling matters most in lane changes and stops with turn signals on. If the right signal also shares a circuit with the hazard function on your Mitsubishi platform, the hazard warning may lose a right-side output too. Confirm all right-side indicators work before you return the vehicle to daily use.

Common Misdiagnoses

Technicians often replace the bulb first and stop there. That wastes time when the socket has heat damage or the ground has high resistance under load. Another common miss involves LED conversions. The Body system expects a certain current draw, so LEDs can trigger B16A4 even when they light. Some techs blame the combination switch. Others condemn the body control module because the code reads like a “bulb outage” message. Avoid those traps by load-testing the right turn output, checking voltage drop at the ground, and inspecting the lamp connector for spread terminals and water intrusion.

Most Likely Fix

The most frequently confirmed repair path starts at the lamp assembly. Verify the right turn bulb type and operation, then inspect the bulb base and socket for discoloration, looseness, or melting. If the bulb tests good, prove the circuit next. Check for proper power on the right turn feed and confirm a solid ground with a voltage-drop test while the lamp loads the circuit. Many Outlander repairs end with cleaning and tightening terminals, repairing a corroded ground, or restoring a damaged pigtail near the lamp housing. Confirm the fix by operating the right signal and hazards and rechecking for code return after a short drive; enable criteria vary by Mitsubishi platform.

Repair Costs

Repair cost depends on whether the confirmed root cause is wiring, connector condition, a sensor, a module, or the labor needed to diagnose the fault correctly.