OBD Guide
ENFRDEESPT

B1E21

Backup Battery Circuit Voltage Below Threshold

B1E21 is an OBD-II diagnostic trouble code meaning: Backup Battery Circuit Voltage Below Threshold. Common causes: low backup battery, damaged wiring harness. 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
  • Error B1E21 in the diagnostic scanner memory
  • Possible problems with the operation of airbags or pretensioners

Causes

  • Low backup battery
  • Damaged wiring harness
  • Poor contact in the circuit
  • Restraint control module malfunction

How to Fix

  1. Check backup battery voltage
  2. Inspect the wiring harness for damage
  3. Check contacts and connections
  4. If necessary, replace the battery or wiring harness
  5. Reset the error and check the system

Related codes

B1E20B1E22B1000

FAQ

What does the B1E21 code mean?

B1E21 is an OBD-II diagnostic trouble code that indicates: Backup Battery Circuit Voltage Below Threshold

What causes a B1E21 error code?

The most common causes of B1E21 include: Low backup battery; Damaged wiring harness; Poor contact in the circuit; Restraint control module malfunction.

How do I fix a B1E21 diagnostic trouble code?

To fix B1E21: Check backup battery voltage. Inspect the wiring harness for damage. Check contacts and connections. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with B1E21?

Do not drive — repair immediately

How much does it cost to fix B1E21?

The estimated repair cost for B1E21 is $56–167. Actual cost depends on your vehicle, location, and labor rates.

FRDEESPT

See also: Russian version · NationStat