B1590 — Autolamp Delay Increase Circuit Short To Ground

What is the most common cause of B1590?

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

What are the symptoms of B1590?

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

Will B1590 clear itself?

Sometimes B1590 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 B1590?

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.

Is it safe to drive with B1590?

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.

Code B1590 points to a specific fault in your vehicle's body electrical system — specifically, a short-to-ground condition in the autolamp delay increase circuit. When the body control module (BCM) or another governing module detects that this circuit's voltage has dropped below acceptable limits, it logs B1590 after confirming the problem across multiple drive cycles. This isn't an engine management code; it's a body electronics issue that affects convenience features like exterior lighting, wipers, power locks, or windows depending on your vehicle's configuration.

The affected module continuously monitors the autolamp delay circuit, watching for voltage levels that indicate proper operation. When readings drift outside the expected range, the system retries the check across successive drive cycles to rule out transient glitches. Once confirmed, the PCM stores the code and illuminates the warning light. Freeze frame data captured alongside B1590 shows engine rpm, load, temperature, and vehicle speed at the moment of detection — use this snapshot to recreate the failure conditions during diagnosis.

Symptoms of B1590

• Dashboard warning light is active
• Engine performance remains unaffected in most applications
• The related function — whether lighting, wipers, locks, or windows — operates intermittently or stops working entirely
• No drivability complaints under normal conditions
• Symptoms may come and go depending on moisture levels or connector condition

Common Causes

• Body control module (BCM) failure or internal circuit fault
• Chafed or broken wiring in door jambs, tailgate hinges, or other flex points
• Faulty switch, motor, or actuator for the affected component
• Blown fuse or failed relay in the affected circuit
• Corroded, loose, or disconnected electrical connectors
• Water intrusion into wiring or connectors near wet areas

Diagnosing B1590

1. Connect an OBD2 scanner and verify that B1590 is stored. Save the freeze frame data — it tells you exactly what the engine was doing when the fault occurred.
2. Pull any related codes too. P0xxx, P1xxx, or other B-codes often point to the real culprit behind B1590. Check for manufacturer TSBs using your VIN on the automaker's site or nhtsa.gov.
3. Visually inspect the wiring harness and connectors tied to the body electrical system. Look for damaged insulation, green or white corrosion buildup, and any signs of overheating.
4. Activate the suspect function (switch on the wipers, operate the locks, etc.) while monitoring the relevant PID values in live data. Watch for erratic readings or no response.
5. Pay close attention to flex locations — door jambs and tailgate openings — where wires bend repeatedly. This is where insulation fails first.
6. Clear B1590, then drive through a complete cycle that mirrors the freeze frame conditions. If the code returns, the fault is still active.

Repair Options and Costs

Start with the cheapest and most likely culprits before replacing major control modules:

• Wiring repair or connector replacement: $80–$250
• Switch or actuator replacement: $120–$450
• BCM repair or full replacement: $300–$900

Diagnosing B1590 correctly before purchasing parts is the smartest move. BCM replacement is rarely the answer — it's usually wiring, connectors, or a failed component instead.

Can You Drive with B1590?

Yes, in most cases B1590 poses no direct threat to drivability. Body electrical faults typically don't affect the engine, transmission, or brakes. That said, exercise caution if the fault involves exterior lighting (night driving becomes hazardous), wipers during rain or snow, or central locking — a car that won't lock properly leaves your vehicle unsecured. Address those issues promptly.

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