B1491 is triggered when monitoring logic identifies an issue with Ignition Cylinder Sensor Circuit Failure affecting body electronics and comfort modules.
B1491 Code: Meaning, Symptoms, Causes & Fix
Overview
Symptoms
- related warning lamp illuminated
- battery draw complaints
- feature inoperative intermittently
Common causes
- Broken terminal inside harness affecting ignition cylinder sensor circuit failure
- Disconnected or loose connector
- Connector pin damage/corrosion or harness stress near related components
How to diagnose B1491
- Confirm B1491 and capture freeze-frame data with a professional scan tool.
- Inspect wiring, connectors, and grounds related to ignition cylinder sensor circuit failure for obvious defects.
- Use a continuity test from module pin to component to identify opens/high resistance.
- Check for related DTCs to identify the root-cause chain before replacing parts.
- After repair, clear codes and confirm readiness monitors complete without recurrence.
Severity of code B1491
Moderate: This code is moderate severity: the vehicle may still operate, but fault progression can increase repair cost over time.
Can you drive with B1491?
Most vehicles can be driven short-term with B1491, 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)
- Repair obvious wiring/connector faults first to prevent repeat parts replacement.
- Address the root fault mode (open) in the ignition cylinder sensor circuit failure circuit/system.
- Apply the required relearn/adaptation procedure if specified by service information.
- Road-test and verify B1491 remains cleared under the conditions that originally set the code.
Fix options
- Restore continuity and verify pin tension.
- Clear corrosion and protect terminals.
- Clear DTCs and verify with live data and completed drive cycle.
Typical repair cost
$160-$850
Common mistakes when diagnosing B1491
- 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.
B1491 in common vehicles
B1491 appears across makes such as Mazda, Subaru, Lexus, Jeep. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.
Frequently asked questions
What causes B1491?
B1491 is commonly set by open faults affecting ignition cylinder sensor circuit failure.
How much does it cost to fix B1491?
For B1491, repair costs are typically $160-$850 depending on exact root cause, labor rates, and part quality.
Can I clear B1491 without repair?
You can clear B1491 temporarily, but the code usually returns until the underlying fault is corrected.