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B0021 Mercury Code - Left Curtain Deployment Control 1

- Code Popularity: 3,087 Views
- Repair Importance Level: 3/3
- Repair Difficulty Level: 3/3
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What are the Possible Causes of the DTC B0021 Mercury?

NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
  • Faulty Driver Side Air Curtain
  • Driver Side Air Curtain harness is open or shorted
  • Driver Side Air Curtain circuit poor electrical connection
⚠ Does your Mercury have Safety Recalls? → Check here

How to Fix the DTC B0021 Mercury?

Review the 'Possible Causes' mentioned above and visually examine the corresponding wiring harness and connectors. Ensure to check for any damaged components and inspect the connector pins for signs of being broken, bent, pushed out, or corroded.

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What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B0021 Mercury code, it typically requires 1.0 hour of labor. The specific diagnosis time and labor rates at auto repair shops can differ based on factors such as the location, make and model of the vehicle, and even the engine type. It is common for most auto repair shops to charge between $75 and $150 per hour.

When is the Code Detected?

If the Restraints Control Module (RCM) detects a short between the driver side air curtain circuits and the circuits of another SRS component, it sets this Diagnostic Trouble Code (DTC) and the DTC of the corresponding SRS component.

What are Code Possible Symptoms?

  • Air Bag Warning Light ON

Code B0021 Mercury Description

The Restraints Control Module (RCM) monitors all deployable device and sensor circuits for a signal cross coupled (short) between circuits. If the RCM detects a short between the circuits of one device and another device, it will store a DTC for each of the signal cross coupled faults in memory. The RCM sends a message to the Instrument Panel Cluster (IPC) to illuminate the air bag warning indicator. When a normal loop fault is present (one loop is either shorted to battery/ground, open circuit or low resistance), then signal cross coupled diagnostics will not be active. Once the normal loop fault is repaired, then the signal cross coupled diagnostics will resume.

OBDII Code B0021 Mercury - Left Curtain Deployment Control 1 - AutoCodes.com
B0021 Mercury Code - Left Curtain Deployment Control 1

Need More Information on the Code?

Need more information on how to fix the B0021 Mercury code? Get Access to Factory Service Manuals

Need Help with the Code?

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Precautions for SRS “AIR BAG” and “SEAT BELT PRE-TENSIONER” Service

  • Never probe the electrical connectors on air bag, side air curtain modules or seat belts.
  • Never disassemble or tamper with safety belt buckle/retractor pretensioners, adaptive load limiting retractors, safety belt inflators, or probe the electrical connectors.
  • Do not use electrical test equipment to check SRS circuits unless instructed to in this Service Manual.
  • Before servicing the SRS, turn ignition switch OFF, disconnect both battery cables and wait at least 3 minutes. For approximately 3 minutes after the cables are removed, it is still possible for the air bag and seat belt pre-tensioner to deploy. Therefore, do not work on any SRS connectors or wires until at least 3 minutes have passed.
Failure to follow this instruction may result in the accidental deployment of these modules, which increases the risk of serious personal injury or death.

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