FAQ
TL;DR: W211 window hums but won’t move? A 6 V test is fine, but “it should be >12 V after firing.” Trace power/ground at the door, repair wiring, and re-test before blaming the relay. [Elektroda, andrzej20001, post #16647580]
Why it matters: This FAQ helps DIYers quickly decide if a W211 window fault is electrical wiring, control module, or motor, and how to verify it safely.
Quick Facts
- Observed case: motor ran again after bypassing weak feed; low voltage at the last segment was the culprit. [Elektroda, gdkj, post #16658770]
- Harness makeup noted: 2 thick power wires to the motor plus ~4 thin signal/sensor leads to the assembly. [Elektroda, gdkj, post #16647399]
- Measured load in-thread: ~2 A while moving and ~6 A stalled, using a 6 V battery. [Elektroda, gdkj, post #16647239]
- Supply expectation: with engine running, window feed should be >12 V at the motor. [Elektroda, andrzej20001, post #16647580]
- Edge case: break found not in hinge area but near a welded fuse socket. [Elektroda, gdkj, post #16668195]
How do I fix a W211 window that hums but won’t move?
Check power and ground to the motor at the door first. The documented fix was repairing a damaged feed near the fuse socket, not replacing the relay. After restoring a solid supply, the window worked normally. “Humming” often means the module commands movement but the motor lacks voltage. Focus on wiring continuity and connections before parts swapping. [Elektroda, gdkj, post #16668195]
What current should a healthy W211 window motor draw?
In the cited case study, the motor drew about 2 A while moving and about 6 A at stall when powered by a 6 V battery. Use this as a reference trend rather than a factory spec. Excessive stall current or abrupt cutoff can also indicate binding or protection triggering. [Elektroda, gdkj, post #16647239]
How do I test motor power with a light-bulb load?
Unplug the motor connector and clip a 12 V test bulb across the two thick motor pins. Press the switch up/down. A bright, steady light indicates good supply; dim or flicker signals a voltage drop. This quick load test reveals weak feeds better than a voltmeter alone. [Elektroda, andrzej20001, post #16647304]
What do the thick and thin wires on the window assembly do?
Two thick wires carry motor power and ground. The additional thin wires serve position or limit sensing and control signaling within the door module assembly. Do not assume the thin leads can power the motor. Verify the heavy pair for voltage under load. [Elektroda, gdkj, post #16647399]
If the motor runs on a 6 V battery, is the mechanism OK?
Yes—if it moves on 6 V, the mechanism and motor are generally capable. The next step is verifying vehicle supply, which should be above 12 V with the engine running. “It should be >12 V after firing.” Check for drops across connectors, grommets, and splices. [Elektroda, andrzej20001, post #16647580]
Where do window wiring breaks occur on the W211?
Breaks often appear where the harness flexes, but this documented failure was elsewhere. The damaged conductor was near a welded fuse socket, not at the hinge area. Inspect both the door grommet and upstream fuse/connector zones to catch this edge case. [Elektroda, gdkj, post #16668195]
What does clicking or humming from the door module mean?
It usually means the module is commanding movement, but the motor isn’t receiving adequate power or ground. Low supply, a high-resistance joint, or protection limiting can prevent rotation. Verify voltage at the thick motor pins while activating the switch. [Elektroda, andrzej20001, post #16647580]
Does the W211 window motor have thermal protection?
Yes. The platform uses thermal protection to prevent overheating during overload or repeated operation. If it trips, the window may pause until the motor cools. Persistent tripping suggests binding or a voltage drop that increases current draw. [Elektroda, Megamax, post #16649976]
Can I use the car’s diagnostics to help with window issues?
Yes. This model supports extensive diagnostics. A scan tool can read door module statuses and faults, helping distinguish wiring loss from module or motor faults. Use diagnostics after basic power and ground tests to save time. [Elektroda, Megamax, post #16649976]
Is the driver’s switch panel using a 1‑wire bus?
No. In this platform, the 1‑wire reference relates to alternator communication, not the window switch network. The door electronics interpret switch inputs and drive the motor locally via the heavy wires. [Elektroda, Megamax, post #16649976]
How can I safely bypass power to confirm a wiring fault?
- Provide a known-good 12 V and ground directly to the two thick motor pins.
- Briefly energize in one polarity, then reverse for the opposite travel.
- If the motor runs, repair the weak feed or splice upstream and re-test.
This confirmed a weak last-segment supply in the case study. [Elektroda, gdkj, post #16658770]
I replaced the relay and nothing changed—what next?
Stop replacing parts. Verify voltage and ground at the motor while commanding the window. The thread shows relay replacement did not help because the fault was a weak feed. Load-test the circuit and inspect splices and the fuse socket area. [Elektroda, gdkj, post #16647239]
What final repair resolved the issue in this case study?
Repairing the damaged power cable near a welded fuse socket. After restoring a solid feed, the driver’s window operated normally. This underscores the need to inspect beyond the door hinge area for intermittent or high-resistance faults. [Elektroda, gdkj, post #16668195]
What are symptoms of low voltage at the motor?
You may hear module humming or clicking, with little or no window movement. A bypass feed makes the glass move normally, confirming supply loss. Dim light-bulb tests at the motor connector also indicate voltage drop under load. [Elektroda, gdkj, post #16658770]
