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B1681

DTC B1681 indicates the Passive Anti-Theft System (PATS) transceiver module fails to receive a valid signal or cannot establish normal communication with the engine control module (PCM/ECM) — Atto 3

Safety System

DTC B1681 indicates the Passive Anti-Theft System (PATS) transceiver module fails to receive a valid signal or cannot establish normal communication with the engine control module (PCM/ECM).

This fault belongs to the Body Security system, not the SRS airbag system (Note: original documentation may misclassify the airbag switch).

The fault triggers the vehicle anti-theft immobilizer, preventing the engine from starting (No Crank/No Start).

The instrument cluster Security Light typically flashes rapidly.

The fault stems from abnormalities in key transponder recognition, 125kHz radio frequency signal transmission at the transceiver coil, or data exchange on the dedicated communication line between the PATS module and the PCM.

Consequently, the PCM cannot verify key validity and inhibits engine starting.

3
Cases Logged
Real-World Cases
BYD DTC AI Analysis

Ford PATS transceiver module communication fault (generic technical principles)

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Symptoms: No-crank condition. Immobilizer light on the dash flashing rapidly. Both factory keys failed to start the vehicle. Fault codes: B1681 (PATS Transceiver Module Signal Not Received) and B2103 (PATS Transceiver Circuit Fault). After clearing, B1681 returned immediately. Diagnosis: Checked power and ground at the PATS transceiver module – both normal. Tested the two data lines between the PATS module and PCM with an oscilloscope. The PCM was sending request signals correctly (white/light green wire switching normally), but the gray/orange wire remained stuck at 12V. The PATS transceiver was not pulling the circuit low to ground to return key information. Repair: Replaced the PATS transceiver module. The oscilloscope showed normal bidirectional communication waveforms. The vehicle started normally.
Original source ↗
BYD DTC AI Analysis

BYD PATS Module Heat-Related Failure Case

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Symptoms BYD models with engine immobiliser (Qin, Song, Tang series) exhibit intermittent no-start. The vehicle starts normally when cold, but once warm, the immobiliser warning light comes on and the starter does not crank. DTC B1681 appears intermittently. Diagnosis Measured PATS module power supply and communication circuits cold — normal. Retested hot: module supply voltage dropped from 12V to below 8V. Inspected PATS module connector under the steering column. Found oxidised and burned pins. When hot, thermal expansion increased contact resistance, starving the module of power and preventing operation. Solution Clean and repair the PATS module connector pins. If needed, add a relay to improve the power supply circuit. If the module is internally damaged, replace it and reprogram the keys.
BYD DTC AI Analysis

GM PATS system communication harness short circuit

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Symptoms: Vehicle would not start. Scan tool displayed DTC B1681; immobiliser system was locked. Diagnosis: Inspected PATS transceiver module externally – no damage found. Measured transceiver coil resistance: 1.2 Ω (normal). Checked communication wiring between the PATS module and PCM. Found damaged harness insulation at the engine bay firewall grommet, causing an intermittent short to body earth. This prevented the PCM from receiving the key signal from the PATS module. Resolution: Repaired the damaged twisted-pair communication wires. Re-insulated and fitted protective sleeving. Re-routed the harness to avoid contact with sharp metal edges. Cleared fault codes; immobiliser system communication returned to normal.
Original source ↗
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Community This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.