B1591 — Autolamp Delay Decrease Circuit Failure

What is the most common cause of B1591?

The most common causes are: damaged wiring in door jambs or wet areas, corroded or loose connectors, faulty switch, motor or actuator of the affected system.

Is it safe to drive with B1591?

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 are the symptoms of B1591?

Drivers most often notice: the affected function (locks, windows, lighting, wipers) works intermittently or not at all, warning light on the dashboard, no impact on engine operation in most cases.

Will B1591 clear itself?

Sometimes B1591 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 much does it cost to fix B1591?

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.

The engine control module logs code B1591 when it finds a problem in the vehicle's autolamp delay decrease circuit. This circuit is part of the body electrical system, which handles features like exterior lighting, power windows, door locks, and windshield wipers. When the autolamp delay function fails, the headlights may turn off immediately after you shut off the engine instead of staying on for the programmed amount of time — or they may not turn on at all when the ambient light sensor triggers them.

To trigger B1591, the control module compares real-time sensor and switch data against factory-defined acceptable ranges. It usually takes more than one failed check before the module confirms the fault and stores the code. When that happens, the ECU also captures a freeze frame — essentially a snapshot showing engine RPM, load, coolant temperature, and vehicle speed the instant the failure occurred. That snapshot is valuable because it tells you exactly what conditions were present when the module detected the problem, which points you toward the right area to investigate first.

Once B1591 is active, the specific function tied to that circuit will likely act up. The dashboard may display a warning light, though the engine itself will keep running normally. The actual symptoms depend on which component the autolamp delay circuit controls on your particular vehicle.

Common Symptoms of B1591

• The autolamp delay feature stops working or behaves inconsistently
• Headlights may turn off immediately instead of staying on for the set duration
• Dashboard warning light related to the body system activates
• The affected function (lighting, locks, windows, or wipers) operates intermittently or not at all
• No noticeable effect on engine performance, acceleration, or fuel economy

What Causes B1591?

• Wiring damage in door jambs or areas prone to moisture accumulation
• Body control module (BCM) internal failure or software corruption
• Malfunctioning switch, motor, or actuator in the affected circuit
• Blown fuse or failed relay supplying power to the autolamp system
• Corroded or loose electrical connectors disrupting signal flow
• Damaged grounding points for the body electrical system

How to Diagnose B1591

1. Plug in an OBD2 scanner and confirm B1591 is stored in the ECU memory. Save the freeze frame data — it records the exact engine and vehicle conditions when the fault first appeared.
2. Look for any other stored trouble codes. Related codes often point to the underlying cause rather than just the symptom. Check for manufacturer TSBs (technical service bulletins) specific to your make, model, and year.
3. Perform a visual inspection of the wiring harness and connectors tied to the body electrical system. Look for worn insulation, broken strands, greenish corrosion, or connectors that are not fully seated.
4. Activate the affected component (headlights, wipers, locks) while monitoring live data on the scanner. Watch the switch and motor PID values to see if they respond correctly.
5. Pay close attention to flex points — places where wires bend repeatedly, such as door jambs and tailgate hinges. Wires break here more often than anywhere else.
6. Clear the code, then drive the vehicle through a complete drive cycle that reproduces the freeze frame conditions. If B1591 returns, you have confirmed an ongoing fault.

Repair Options with Costs

• Replace the faulty switch, motor, or actuator: $120–$450 (parts and labor)
• BCM repair or replacement: $300–$900 (parts and labor)
• Repair damaged wiring or connectors: $80–$250 (parts and labor)

How Much Does It Cost to Fix B1591?

The total repair bill hinges on which component is actually faulty. At independent shop rates in the United States, replacing a switch or actuator typically runs $120 to $450. If the body control module needs to be repaired or swapped out, expect $300 to $900. Wiring and connector repairs are usually the least expensive route, ranging from $80 to $250. Across all possible repair paths, fixing B1591 generally costs between $80 and $900. Getting a precise diagnosis before purchasing parts is the smartest move — the most expensive fix is rarely the one you need.

Can You Drive with B1591?

In most cases, yes. Body electrical codes like B1591 typically do not affect engine operation, transmission function, or overall drivability. That said, the underlying fault can become a safety concern depending on which system is affected. If the failure involves exterior lighting or windshield wipers, address it promptly — especially before driving in rain, snow, or darkness. Central locking malfunctions can also leave your vehicle unsecured, which is worth resolving as soon as possible.

Related OBD2 Codes

• B1500: Lamp Turn Signal Left Circuit Open
• B1501: Lamp Turn Signal Left Circuit Short To Battery
• B1502: Lamp Turn Signal Left Circuit Short To Ground
• B1503: Lamp Turn Signal Right Circuit Failure
• B1504: Lamp Turn Signal Right Circuit Open
• B1505: Lamp Turn Signal Right Circuit Short To Battery