B1246 — PTS Parktronic: A42b1 (left outer sensor, front bumper) The plug connection has poor contact

Causes

• Corroded or contaminated sensor connector pins
• Loose or pushed‑out terminal in the sensor plug
• Damaged or chafed wiring harness between sensor and PTS control unit
• Moisture/water ingress in connector or sensor housing
• Faulty sensor or internal connector fault
• Poor repair or poorly seated connector after bumper removal

Symptoms

• Parktronic (PTS) warning or fault lamp/message
• Front left sensor not functioning or reported as faulty in scan tool
• Reduced or asymmetric obstacle detection on front left side
• Intermittent operation or false/constant beeping from PTS
• DTC stored in PTS/vehicle network

What to check

• Read fault memory with Mercedes‑compatible scan tool; note freeze frame and occurrence count
• Check live data / sensor status for A42b1 while activating PTS (ignition on, parking mode if required)
• Visually inspect left outer front sensor, connector and wiring for damage, corrosion, moisture or poor routing
• Perform a wiggle test: move wiring and connector while watching live data for intermittent changes
• Backprobe sensor connector to verify supply voltage present with ignition on and ground continuity to chassis
• Check continuity between sensor connector and PTS module connector; inspect for high resistance or opens

Signal parameters

• Supply power present at sensor connector with ignition on (battery voltage or switched supply per factory data)
• Good ground continuity between sensor housing/ground pin and chassis ground
• Signal line should show activation pulses/waveform when PTS is commanded (verify with scope or oscilloscope)
• No short to ground or to battery on sensor signal or supply lines
• Connector terminal-to-terminal continuity between sensor plug and Parktronic module (per wiring diagram)

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