B2171

Code

Generic B — Body

Sunroof Control Module Fault

Brand: Generic

Type: B — Body

Views: UK: 27 EN: 38 RU: 25

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Failed or intermittent sunroof control module
Poor power supply (blown fuse, faulty relay, low battery voltage)
Bad ground or high-resistance ground connection
Corroded or loose connector(s) at the module or switches
Water intrusion into the sunroof area or module connector
Damaged wiring harness (short to battery/ground or open)

Symptoms

Sunroof does not operate (no response to switch)
Intermittent operation or works only in one direction (open/close)
Sunroof stuck open or stuck closed
Instrument cluster or HVAC may show sunroof-related warning or DTC indicator
Audible clicking or relay noise from module area
Other body systems may show related communication faults

What to check

Read all stored and pending codes and review freeze-frame data with scan tool
Verify vehicle battery voltage (12.2–14.5 V) with key on/engine running
Inspect fuses and relays related to sunroof circuit
Visually inspect module connector and harness for corrosion, water, bent pins, or damaged insulation
Check for DTCs on CAN/LIN network devices that communicate with the sunroof module
Verify ground integrity (measure voltage drop to chassis ground while operating)

Signal parameters

Module supply voltage: ~12 V with ignition on (should be within 11–14.5 V)
Module ground: near 0 V; voltage drop
CAN bus idle voltage: ~2.5 V on CAN_H and CAN_L (differential present)
LIN bus idle voltage (if used): ~12 V through pull-up or specified by manufacturer; signal toggles when active
Switch input voltage: close to battery voltage when pressed (or specified logic level if low-voltage switch)
Position sensor (potentiometer) output: varies with travel (consult service manual for expected range)

Diagnostic algorithm

Connect a capable scan tool. Read and record all codes, freeze-frame, and live data. Note related communication codes.
Clear codes and attempt to cycle the sunroof to see if DTC returns and if operation is reproducible.
Visually inspect sunroof area, drains, and module connectors for water, corrosion, or damage. Repair any water intrusion paths.
Check fuses/relays for the sunroof circuit; replace if blown and investigate cause of blown fuse.
Verify battery and charging system voltage. Perform voltage drop test on power feed and ground to the module while operating the sunroof.
Back-probe module connector: confirm constant/ignition-switched power and ground are present. Compare to expected values.
Monitor communication lines (CAN/LIN) on the module with a scope or lab-grade scan tool. Resolve any bus faults (terminations, other module failures).
Test switch inputs and position sensors for correct signals while commanding the sunroof. Replace switch if faulty.
Test sunroof motor: check continuity, measure current draw during operation, and ensure no mechanical binding. Repair mechanical issues or motor as needed.
If electrical and mechanical checks are good but fault persists, consult manufacturer bulletin/repair manual for module reflash/update procedures. Reprogram or replace module per service instructions.
After repair or module replacement, clear codes and perform full function test including auto-close/relearn procedures. Confirm no related codes return.

Likely causes

Corroded/loose connector at the sunroof control module from water intrusion
Failed module electronics due to moisture or age
Blown fuse or weak battery/voltage drop to the module
Intermittent CAN/LIN bus communication fault between modules
Wiring short or open in the motor/switch circuit causing module error

Fault status

⚠️ Status

Stored DTC B2171 — Sunroof Control Module Fault. Sunroof function may be disabled or intermittent. Further diagnosis required to identify electrical, communication, or module hardware cause.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0-3.0 hours