U0170

Code

Generic U — Network/User

Lost Communication With Restraints System Sensor A

Brand: Generic

Type: U — Network/User

Views: UK: 21 EN: 34 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Open or shorted communication wiring (CAN/LIN) between sensor A and restraints control module
Faulty restraint sensor A
Poor or corroded connector pins at the sensor, module, or splice
Loss of power or ground to the sensor or restraints control module
Faulty restraints control module (RCM/SRM) or gateway module
Damaged or missing termination resistor(s) on the vehicle bus

Symptoms

SRS/airbag warning lamp illuminated
Related restraints system features may be disabled or flagged in diagnostics
Stored U0170 and possibly other communication or restraints-related codes
Intermittent or permanent loss of sensor data when monitored with a scan tool

What to check

Visually inspect sensor A connector, harness, and nearby wiring for damage, corrosion, contamination, or pin push-out
Check for water damage or recent collision/repair evidence near the sensor or harness
Use a scan tool to verify U0170 and look for related codes and freeze frame data
Monitor live data/communication on the restraints network for presence of sensor A messages
Check power and ground circuits for the sensor and the restraints control module (verify proper voltages and good grounds)
Verify CAN/LIN bus continuity and termination resistor values at the module ends (typically two 120Ω in parallel → ~60Ω across CAN H/L)

Signal parameters

Typical CAN idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (each), differential ≈ 0 V; dominant state: CAN_H ≈ 3.5–3.75 V, CAN_L ≈ 1.25–1.5 V; differential ≈ 2–3 V (vehicle-specific)
CAN bus termination: ~60 Ω measured across CAN_H and CAN_L (two 120 Ω in parallel)
Common CAN bit rates: 250 kbps or 500 kbps (confirm vehicle specification)
If sensor uses LIN: idle ~battery voltage via pull-up, dominant low ≈ 0 V, typical LIN baud 19.2 kbps (vehicle-specific)
Sensor power: vehicle-specific (often switched 12 V with a fused feed) and chassis/return ground — verify nominal battery voltage at harness with ignition on

Diagnostic algorithm

Safety first: follow SRS safety procedures — disconnect battery only per manufacturer guidance and observe required wait times before servicing airbag/SRS connectors. Use insulated tools and avoid unnecessary connector disturbance.
Read and record codes and freeze-frame data with a capable scan tool. Note any additional communication or restraints codes.
Visually inspect sensor A connector, wiring, and mounting. Look for corrosion, bent pins, pushed-out terminals, moisture, or physical damage.
With ignition on (and following safety procedures), verify sensor power/ignition feed and ground at the sensor connector using a multimeter. Compare to vehicle nominal battery voltage and good ground.
Backprobe CAN_H and CAN_L at the sensor connector and at the restraints control module. Verify idle voltages, dominance on bus activity, and correct termination resistance (~60 Ω). Use oscilloscope if available to view bus signals and noise.
Monitor the restraints network with the scan tool. Attempt to request sensor data or view live messages. Perform a wiggle test on the harness and connectors while watching for dropouts or new codes.
Check continuity between sensor pins and the restraints control module pins to detect opens or high-resistance connections. Also check for shorts to battery or ground.
Inspect connectors and harness routing for chafing points, especially under seats and through seatbelt anchor areas. Repair any damaged wiring using proper solder/crimp and heat-shrink or OEM repair splices.
If wiring and connectors test OK, consider replacing sensor A with a known-good unit or swapping with an identical known-good sensor (if applicable) to check for sensor failure. Re-scan for codes after replacement.
If communication is still lost and wiring/sensor are good, inspect or test the restraints control module and gateway for faults; check module power/ground and perform reprogramming or module replacement only per OEM procedures.
Clear codes and perform a functional test/road test and recheck for recurrence. Document repairs and verify SRS light behavior and absence of communication faults.

Likely causes

Disconnected or loose sensor connector at the seat or sensor location
Broken/chafed wiring harness in the seat or under-hood area
Corroded pins or moisture intrusion in connector
Faulty sensor A
Faulty or unpowered restraints control module

Fault status

⚠️ Status

U0170 — Lost Communication With Restraints System Sensor A. Communication with the specified restraints sensor is not detected by the restraints control module or network.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours