B1591 Code: Meaning, Symptoms, Causes & Fix

Overview

Symptoms

• battery draw complaints
• related warning lamp illuminated
• module resets or glitches

Common causes

• Open circuit in wiring affecting autolamp delay decrease circuit failure
• Broken terminal inside harness
• Connector pin damage/corrosion or harness stress near related components

How to diagnose B1591

1. Confirm B1591 and capture freeze-frame data with a professional scan tool.
2. Inspect wiring, connectors, and grounds related to autolamp delay decrease circuit failure for obvious defects.
3. Use a continuity test from module pin to component to identify opens/high resistance.
4. Check for related DTCs to identify the root-cause chain before replacing parts.
5. After repair, clear codes and confirm readiness monitors complete without recurrence.

Severity of code B1591

Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.

Can you drive with B1591?

Most vehicles can be driven short-term with B1591, but postpone heavy load/highway driving until repaired.

If the warning lamp is flashing or drivability/safety is affected, avoid driving and diagnose immediately.

How to fix it (step-by-step)

1. Repair obvious wiring/connector faults first to prevent repeat parts replacement.
2. Address the root fault mode (open) in the autolamp delay decrease circuit failure circuit/system.
3. Apply the required relearn/adaptation procedure if specified by service information.
4. Road-test and verify B1591 remains cleared under the conditions that originally set the code.

Fix options

• Repair open circuit and secure connector lock.
• Restore continuity and verify pin tension.
• Clear DTCs and verify with live data and completed drive cycle.

Typical repair cost

$160-$850

Common mistakes when diagnosing B1591

• Replacing parts without verifying voltage, ground, and signal integrity first.
• Ignoring related stored/pending codes that indicate upstream faults.
• Skipping post-repair verification drive cycle and readiness checks.

B1591 in common vehicles

B1591 appears across makes such as Ford, Toyota, Honda, Chevrolet. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes B1591?

B1591 is commonly set by open faults affecting autolamp delay decrease circuit failure.

How much does it cost to fix B1591?

For B1591, repair costs are typically $160-$850 depending on exact root cause, labor rates, and part quality.

Can I clear B1591 without repair?

You can clear B1591 temporarily, but the code usually returns until the underlying fault is corrected.

Helpful tools

• Estimate repair cost
• Decode your VIN
• Calculate fuel cost