Code Definition

P1816 — Transmission Neutral Safety Switch Circuit Failure

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

About P1816

P1816 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 P1816 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.

P1816 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 Powertrain Control Module (PCM) or Transmission Control Module (TCM) detects an invalid or inconsistent signal from the neutral safety switch circuit. The neutral safety switch (also known as the park/neutral position switch or range switch) signals whether the transmission is in Park or Neutral, enabling engine start and affecting certain control logic. If the input signal is missing, outside of expected voltage parameters, or does not match other transmission range signals, the PCM sets P1816.

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