B1390 Code: Meaning, Symptoms, Causes & Fix

Overview

Symptoms

• related warning lamp illuminated
• battery draw complaints
• feature inoperative intermittently

Common causes

• Disconnected or loose connector affecting oil temperature sensor circuit short to ground
• Open circuit in wiring
• Connector pin damage/corrosion or harness stress near related components

How to diagnose B1390

1. Confirm B1390 and capture freeze-frame data with a professional scan tool.
2. Inspect wiring, connectors, and grounds related to oil temperature sensor circuit short to ground 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 B1390

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

Can you drive with B1390?

Most vehicles can be driven short-term with B1390, 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 oil temperature sensor circuit short to ground circuit/system.
3. Apply the required relearn/adaptation procedure if specified by service information.
4. Road-test and verify B1390 remains cleared under the conditions that originally set the code.

Fix options

• Repair open circuit and secure connector lock.
• 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 B1390

• 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.

B1390 in common vehicles

B1390 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 B1390?

B1390 is commonly set by open faults affecting oil temperature sensor circuit short to ground.

How much does it cost to fix B1390?

For B1390, repair costs are typically $160-$850 depending on exact root cause, labor rates, and part quality.

Can I clear B1390 without repair?

You can clear B1390 temporarily, but the code usually returns until the underlying fault is corrected.

Helpful tools

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