Field Guide · protocol

Also known as: TPMS, tire pressure monitoring system

TPMS (tire-pressure monitoring system) is the short-range radio link by which direct tire sensors report each wheel’s pressure and temperature to the car.1 A battery-powered sensor inside each tire wakes periodically (or on pressure change / rotation) and transmits a brief burst on a sub-GHz ISM band — 315 MHz in North America, 433.92 MHz in Europe — carrying a unique sensor ID plus the measured values. Because these bursts are simple OOK/FSK packets in the clear, they are among the easiest signals to receive with a general-purpose SDR.

ECU OOK burst: preamble · ID · pressure · temperature · CRC
Each tire sensor sends a short OOK/FSK burst carrying its ID, pressure, and temperature to the vehicle's receiver.

Overview

Direct TPMS puts a small sensor module in each wheel, powered by a long-life battery. It transmits infrequently to conserve power, so the receiver in the car body listens continuously and matches incoming IDs to learned wheel positions. (Indirect TPMS, by contrast, uses no radio at all — it infers low pressure from wheel-speed differences via ABS sensors.)

Technical characteristics

Property Value
Bands 315 MHz (US), 433.92 MHz (EU) ISM
Modulation OOK/ASK or FSK
Line coding Commonly Manchester or differential Manchester
Payload 32-bit sensor ID, pressure, temperature, status/battery
Integrity Checksum or CRC per protocol
Trigger Periodic, motion, or a 125 kHz LF activation tone

Formats are vendor-specific (Schrader, Continental, Pacific, and others), so decoders keep a library of per-manufacturer framings.

History

Direct TPMS spread after regulations mandated pressure monitoring — notably the US TREAD Act, which required systems on new light vehicles from the mid-2000s, with the EU following for new cars around 2014.2 Those mandates made 315/433 MHz TPMS bursts one of the most common signals on the road.

Deployment

Essentially every modern passenger vehicle with direct TPMS emits these bursts, making them a familiar sight for hobbyists surveying the 315/433 MHz ISM bands alongside remote keyless entry and other short-range devices.

Decoding it with GopherTrunk

GopherTrunk does not decode TPMS — it targets trunked land-mobile voice, not vehicle telemetry. TPMS is, however, genuinely receivable with general SDR tools: an RTL-SDR tuned to 315 or 433.92 MHz with a decoder such as rtl_433 will print sensor IDs, pressures, and temperatures directly, since the frames are typically unencrypted. That capability lives in those tools rather than in GopherTrunk.

Sources

  1. Tire-pressure monitoring system — Wikipedia, for direct vs indirect TPMS, the sensor bursts, and payload contents. ↩

  2. ISM radio band — Wikipedia, for the 315/433 MHz bands TPMS shares with other short-range devices. ↩

See also