OBD Guide
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B2021

Open In Left Side Lower MOS

B2021 is an OBD-II diagnostic trouble code meaning: Open In Left Side Lower MOS. Common causes: broken or damaged wiring harness, oxidation of contacts in connectors. Estimated repair cost: $56–167.

Severity
⚠️ Medium
Can you drive?
Do not drive — repair immediately
Approx. repair cost
$56–167 (est.)

Symptoms

  • The passive safety system fault indicator is on
  • The airbag may not deploy in an accident.
  • The error is stored in the ECU memory

Causes

  • Broken or damaged wiring harness
  • Oxidation of contacts in connectors
  • MOS sensor malfunction
  • Problems with the restraint control module

How to Fix

  1. Check the integrity of the wiring harness
  2. Clean the contacts in the connectors
  3. Check MOS sensor resistance
  4. Scan the system for other errors
  5. If necessary, replace the sensor or wiring harness

Related codes

B2020B2022B1010

FAQ

What does the B2021 code mean?

B2021 is an OBD-II diagnostic trouble code that indicates: Open In Left Side Lower MOS

What causes a B2021 error code?

The most common causes of B2021 include: Broken or damaged wiring harness; Oxidation of contacts in connectors; MOS sensor malfunction; Problems with the restraint control module.

How do I fix a B2021 diagnostic trouble code?

To fix B2021: Check the integrity of the wiring harness. Clean the contacts in the connectors. Check MOS sensor resistance. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B2021?

Do not drive — repair immediately

How much does it cost to fix B2021?

The estimated repair cost for B2021 is $56–167. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat