Code Definition

P1820 — Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Generic

About P1820

P1820 is a manufacturer-specific powertrain diagnostic trouble code. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1820 is stored, the module has detected an electrical-circuit fault in the wiring, connector, or driver associated with the named component.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1820 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

This DTC is set when the Transfer Case Control Module (TCCM) or Powertrain Control Module (PCM) detects an electrical fault in the clockwise shift relay coil circuit. The clockwise shift relay controls motor direction in transfer cases equipped with an electric shift motor, enabling mode transitions (e.g., 2HI to 4HI or 4LO) by energising the shift motor in the clockwise direction. If the coil circuit shows signs of an open, short, or unexpected resistance, the module sets P1820.

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