B1507 – Turn signal circuit open (Toyota)

B1507 means your 2015 Toyota Auris has a turn signal circuit that the body system sees as electrically “open.” For most drivers, that shows up as a turn signal that does not flash on one side, flashes fast, or works only sometimes. According to Toyota factory diagnostic data, this is a Toyota-defined body DTC meaning “Turn signal circuit open.” An open circuit does not prove a bad bulb or switch. It tells you the control module cannot see the expected electrical load or feedback in the turn signal path.

B1507 Quick Answer

B1507 on Toyota points to an open circuit in the turn signal system. Start by confirming which lamp does not operate, then test for power, ground, and continuity at the lamp connector before replacing parts.

What Does B1507 Mean?

Official definition: “Turn signal circuit open.” In plain terms, the body system detects that the turn signal circuit cannot carry current as expected. In practice, the affected turn signal may stop working, flash rapidly, or work intermittently because the circuit opens under vibration or load.

What the module checks: On Toyota body systems, a control module commands the turn signal output and monitors the circuit’s electrical response. The module expects a normal load and a stable path from power through the lamp and back to ground. Why that matters: The DTC points to a suspected trouble area in the circuit path, not a confirmed failed lamp or module. You must prove the open with voltage-drop and continuity tests under load.

Theory of Operation

Under normal operation, the Toyota body system uses the turn signal switch request to command left or right turn outputs. Current flows through fuses, wiring, lamp sockets, and grounds. The system may also use the cluster indicator and exterior lamp load to confirm proper operation.

B1507 sets when the module commands a turn signal output but does not see the expected electrical response. An open can come from a burned-out bulb filament, a spread socket terminal, corrosion in a connector, a broken wire in a flex area, or a poor ground that opens under load. Because the module only “sees” circuit behavior, you confirm the fault by measuring voltage at the lamp and verifying a solid ground return.

Symptoms

You will usually notice a turn signal problem before you ever plug in a scan tool.

• Inoperative signal One turn signal does not flash outside the vehicle
• Fast flash The turn indicator on the cluster blinks faster than normal
• Intermittent operation The signal works sometimes, then quits with bumps or steering movement
• Dim lamp The affected corner lamp glows weakly or changes brightness
• Hazard anomaly Hazards may work differently than turn signals on the same side
• Cluster indicator issue The dash arrow may not illuminate, or it may flash erratically
• Related lighting oddities A brake/park lamp in the same housing may act abnormal due to shared ground

Common Causes

• Open in turn signal feed or return wire: A broken conductor stops current flow, so the Toyota body control logic sees an open circuit when it commands the turn signal.
• High-resistance connector at a lamp or junction: Corrosion or a spread terminal reduces current enough that the module interprets the circuit as open.
• Damaged harness at a flex or pinch point: Repeated movement near the tailgate, fender, or steering column can fracture copper inside the insulation and create an intermittent open.
• Blown fuse or poor fuse contact: A failed fuse element or loose fuse fit removes power to part of the turn signal circuit and triggers an open-circuit fault.
• Faulty turn signal bulb/socket contact: A burned bulb filament or a heat-damaged socket can break the load path the module expects to see.
• Incorrect bulb type or wrong LED conversion: Some aftermarket LEDs change circuit load and feedback, which can mimic an open circuit on Toyota monitoring.
• Water intrusion in lamp housing: Moisture promotes corrosion on terminals and splices, which raises resistance until the circuit effectively opens.
• Internal fault in the switching module logic: A failure inside the body-related controller or its output driver can stop command voltage from reaching the turn signal circuit.

Diagnosis Steps

You need a scan tool that can access Toyota body systems, not just generic OBD. Use a digital multimeter, a test light or fused jumper, and basic back-probing tools. Plan on doing voltage-drop testing under load. Have wiring diagrams for the 2015 Auris turn signal circuit path and connector views for lamp assemblies.

1. Confirm DTC B1507 and record freeze frame data. Focus on battery voltage, ignition state, and any switch status PIDs tied to turn signals or hazard operation. Compare stored vs pending status, since a hard open often returns immediately after key-on.
2. Perform a quick visual inspection before meter work. Check the exterior lamps for the affected side and verify bulb type matches Toyota specifications. Look for obvious water in the lamp, melted sockets, or a loose lamp connector.
3. Check related fuses and power distribution next. Inspect fuses feeding the body/turn signal circuits and any integration relay outputs shown in service information. Do not trust a visual fuse check alone, so verify power on both fuse tabs with ignition ON.
4. Verify module power and grounds under load using voltage-drop testing. Command a turn signal ON or hazards ON, then measure ground drop from the module ground pin to battery negative. Keep ground drop under 0.1V with the circuit operating. Also check power feed drop from battery positive to the module power pin during the command.
5. Use the scan tool to run active tests or view data list items. Command left and right turn outputs, if supported, and watch for output status changes. If the module shows command ON but the lamp stays dark, you now have a circuit-level problem to isolate.
6. Check the turn signal load at the lamp connector. With the circuit commanded ON, test for battery voltage at the lamp feed terminal and a solid ground at the ground terminal. If voltage exists but the lamp does not illuminate, focus on the bulb, socket tension, and terminal condition.
7. If voltage does not reach the lamp, work upstream through connectors and junctions. Back-probe the next connector inboard and repeat the loaded voltage check. A voltage present inboard but missing outboard identifies the open between those points.
8. Perform a wiggle test while monitoring live data and lamp operation. Move the harness at known flex areas and connector backshells. Use a scan tool snapshot during this test to capture the moment the circuit drops out, since freeze frame only shows conditions when the DTC set.
9. Check for high resistance that mimics an open by measuring voltage drop across connectors and splices under load. Command the lamp ON, then measure across each connector (pin to pin across the connection). Any significant drop across a single connection points to corrosion, a spread terminal, or a poor crimp.
10. If you suspect an internal module output issue, confirm the circuit integrity first. Use a fused jumper or test light load to verify the downstream wiring and lamp can carry current. If the circuit proves good but the module output never drives, follow Toyota service information for controller pin testing and replacement criteria.
11. Clear codes and confirm the repair. Cycle ignition, operate left/right turn and hazards, and run a short drive if needed. Verify B1507 does not return as pending or confirmed, and confirm normal flash rate and indicator behavior.

Professional tip: Do not rely on continuity checks for an “open circuit” callout. Many Auris harness faults act intermittent, and a few strands can pass a continuity beep. Load the circuit with the actual lamp or a test light, then use voltage-drop to find the exact connection that fails under current.

Possible Fixes

• Repair the open wire section with proper splicing and sealing after you locate the exact break point.
• Clean corrosion and restore terminal tension at the lamp connector or junction connector, then apply appropriate terminal protection.
• Replace a damaged bulb socket or lamp sub-harness after confirming voltage and ground reach the connector.
• Correct an incorrect bulb or remove an incompatible LED conversion, then retest circuit monitoring.
• Repair water intrusion sources and replace affected terminals to prevent repeat high resistance.
• Replace a failed fuse and correct the underlying short or overload if the fuse blew.
• Replace the related Toyota body control module or output driver only after you prove wiring, loads, and grounds operate correctly.

Can I Still Drive With B1507?

You can usually drive a 2015 Toyota Auris with DTC B1507, but you should treat it as a safety defect. This code points to an open circuit in the turn signal circuit. Other drivers rely on your turn signals to predict your next move. If one side does not flash, flashes fast, or works intermittently, avoid highway lane changes and heavy traffic until you confirm operation. Use hand signals if you must move the vehicle. If the hazard lamps also fail or the cluster turn indicator stays dark, stop and diagnose. Those symptoms often indicate a shared power, ground, or connector issue.

How Serious Is This Code?

B1507 ranges from an inconvenience to a real road-safety issue. When only one exterior lamp fails but the rest of the system works, the vehicle still drives normally. The risk rises because other drivers lose your intent signal. When multiple turn lamps, the dash indicator, or the hazards stop working, the concern becomes higher. An open circuit can also create intermittent operation that comes and goes with bumps. That unpredictability causes close calls in merges and turns. This code does not usually create a no-start or engine drivability problem. It can still cause a failed inspection in areas that check lighting operation.

Common Misdiagnoses

Technicians often jump straight to a bulb or LED assembly without proving the open circuit. That wastes time when the real fault sits in a connector, ground splice, or harness bend point. Another common mistake involves chasing the flasher function. On many Toyotas, the body ECU logic controls flashing, so the “flasher” diagnosis starts with circuit integrity, not a separate relay. Shops also miss loaded testing. A meter can show voltage with the lamp unplugged, yet the circuit opens under load from corrosion. Finally, some clear the code after a visual check and call it fixed. Always confirm turn and hazard operation, then recheck for pending codes.

Most Likely Fix

The most common confirmed repair path for B1507 involves finding and repairing an open in the turn signal lamp feed or return path. Start at the affected lamp connector and work back toward the body harness. Look for backed-out terminals, water intrusion, and broken conductors near hinges and bumper-to-body transitions. After you restore circuit continuity, verify the circuit carries current under load and that the turn signal and hazards operate steadily. If the circuit tests good end-to-end, shift to the switch input and body ECU connector checks. Do not replace a body ECU until you prove power, grounds, and signal paths.

Repair Costs

Repair cost depends on whether the confirmed root cause is a sensor, wiring, connector issue, or control module problem. Verify the fault electrically before replacing parts.

Last updated: April 3, 2026