OBD Guide
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C2121

No Signal from Transmitter ID 1 In Main Mode

C2121 is an OBD-II diagnostic trouble code meaning: No Signal from Transmitter ID 1 In Main Mode. Common causes: transmitter id 1 fault, open or short circuit in 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
  • Lack of response from the passive safety system in an accident
  • Unstable operation of the passive safety system

Causes

  • Transmitter ID 1 fault
  • Open or short circuit in wiring harness
  • Problems with the control unit
  • Poor contact in connectors

How to Fix

  1. Check the integrity of the wiring harness
  2. Check connection of transmitter ID 1
  3. Check the functionality of the ID 1 transmitter
  4. Check the control unit for other errors
  5. Replace ID 1 transmitter if necessary

Related codes

B0001B0002B1000

FAQ

What does the C2121 code mean?

C2121 is an OBD-II diagnostic trouble code that indicates: No Signal from Transmitter ID 1 In Main Mode

What causes a C2121 error code?

The most common causes of C2121 include: Transmitter ID 1 fault; Open or short circuit in wiring harness; Problems with the control unit; Poor contact in connectors.

How do I fix a C2121 diagnostic trouble code?

To fix C2121: Check the integrity of the wiring harness. Check connection of transmitter ID 1. Check the functionality of the ID 1 transmitter. For a complete diagnosis, use an OBD-II scanner.

Is it safe to drive with C2121?

Do not drive — repair immediately

How much does it cost to fix C2121?

The estimated repair cost for C2121 is $56–167. Actual cost depends on your vehicle, location, and labor rates.

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See also: Russian version · NationStat