B1391 Code: Meaning, Symptoms, Causes & Fix

Overview

B1391 is triggered when monitoring logic identifies an issue with Oil Level Switch Circuit Failure affecting body electronics and comfort modules.

Symptoms

feature inoperative intermittently
module resets or glitches
related warning lamp illuminated

Common causes

Open circuit in wiring affecting oil level switch circuit failure
Broken terminal inside harness
Connector pin damage/corrosion or harness stress near related components

How to diagnose B1391

Confirm B1391 and capture freeze-frame data with a professional scan tool.
Inspect wiring, connectors, and grounds related to oil level switch 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 B1391

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

Can you drive with B1391?

Most vehicles can be driven short-term with B1391, 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 oil level switch circuit failure circuit/system.
Apply the required relearn/adaptation procedure if specified by service information.
Road-test and verify B1391 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 B1391

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.

B1391 in common vehicles

B1391 appears across makes such as BMW, Mercedes-Benz, Audi, Volvo. Failure patterns differ by platform: wiring routes, software calibration, and component supplier revisions can change root cause.

Frequently asked questions

What causes B1391?

B1391 is commonly set by open faults affecting oil level switch circuit failure.

How much does it cost to fix B1391?

For B1391, repair costs are typically $160-$850 depending on exact root cause, labor rates, and part quality.

Can I clear B1391 without repair?

You can clear B1391 temporarily, but the code usually returns until the underlying fault is corrected.