Engine-Codes
 
OBDII Code List
 
B0021 MERCURY

B0021 MERCURY - Left Curtain Deployment Control 1

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3  What does this mean?

B0021 MERCURY Possible Causes

  • Faulty Driver Side Air Curtain
  • Driver Side Air Curtain harness is open or shorted
  • Driver Side Air Curtain circuit poor electrical connection

Cost of diagnosing the B0021 MERCURY code

    Labor: 1.0

    The cost of diagnosing the B0021 MERCURY code is 1.0 hour of labor. The auto repair labor rates vary widely across the country, and even within the same city. Most auto repairs shops charge between $75 and $150 per hour.

When is the B0021 MERCURY 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.

B0021 MERCURY Possible Symptoms

  • Air Bag Warning Light ON

B0021 MERCURY Meaning

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 - Engine-Codes.com

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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