Mercedes-Benz CLA Alternator: Specs, Fitment & Common Faults
A genuinely alarming, honest account: a battery warning light was initially quoted at £420 for a full alternator replacement, but the actual cause was a seized tensioner pulley bearing — the alternator itself was completely fine.
Illustration for editorial purposes
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OEM Part Number: confirm via VIN — alternators (aftermarket) Bosch 1 986 A01 041 / Valeo 444471
| Alternators (aftermarket) | Bosch 1 986 A01 041 (150 A, freewheel pulley, 5 ribs, 52.3 mm, new, plug 181, excludes vacuum pump); Bosch 0 986 082 150 (150 A, rigid multi-rib pulley, 5 ribs, 54 mm, remanufactured exchange, plug PL166, core charge £47.03, excludes vacuum pump); Valeo 444471 (175 A, freewheel pulley, 6 ribs, 55 mm, remanufactured exchange, core charge £50.24); Hella 8EL 011 713-551 (150 A, freewheel pulley, 5 ribs, 53 mm, new); AS-PL A0545S (150 A, freewheel pulley, 5 ribs, 52 mm, new, plug PL_2306); AS-PL A0811S (175 A, freewheel pulley, 6 ribs, 55 mm, new, plug PL_2306); Rotovis 9090817 (150 A, freewheel pulley, 5 ribs, 52 mm, remanufactured, COM plug). |
|---|---|
| Outputs & variants | 150 A five-rib 52-54 mm units for the M270 petrol engines (CLA 180/200/250) in freewheel or rigid-pulley form; 175 A six-rib 55 mm freewheel units for the OM651 diesels (CLA 200 d/220 d). The parts are shared with the W176 A-Class and X156 GLA. |
| Genuine (OE) numbers quoted | 0125711043 (AS-PL A0811S); 0125711028 (AS-PL A0531S); 0125711030 (AS-PL A0545S); 0125711093 (AS-PL A0545(SEG)). |
| Fitment notes | Petrol and diesel use different rib counts (5 against 6) and belts, so count the ribs on the old pulley before ordering; all engines have start-stop with a COM/LIN-controlled alternator, and exchange units from Bosch, Valeo and Walker carry core charges of £25-£50. |
Mercedes-Benz CLA Alternator: Often Blamed on the Battery Instead
On the Mercedes-Benz CLA, a weak battery and a failing alternator produce almost identical symptoms at first — dim lights, slow starts, a car that won't hold charge — which is exactly why so many people replace the battery, only to be back at the garage a few weeks later with the real culprit untouched.
Mercedes-Benz CLA Alternator: What It Does
The Mercedes-Benz CLA's alternator generates electricity while the engine runs, charging the battery and powering the car's electrical systems directly. A healthy alternator means the battery is mostly there for starting the engine and covering brief demand spikes — not for actually running the car's electronics on its own.
Mercedes-Benz CLA Alternator: Watch: Replacing It
C117 CLA 250 M270 engine.
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A Genuinely Alarming, Honest Real Account Worth Knowing — Mercedes-Benz CLA Alternator
If the battery warning light has come on, this is genuinely worth knowing before paying for a full alternator replacement: one documented case saw a battery warning light initially quoted at £420 fully fitted for a complete alternator replacement, but the actual root cause turned out to be a seized tensioner pulley bearing rather than a genuine alternator failure. Once this bearing loses its lubrication, the drive belt begins sliding rather than gripping properly, eventually destroying itself and stopping the alternator being driven entirely — triggering the exact same warning light as a genuine alternator failure, even though the alternator itself is completely fine.
It's also genuinely worth knowing that the pulley driving the alternator on many of these engines is a genuine one-way clutch mechanism, allowing the alternator's rotor to coast down gently to a stop rather than being abruptly halted.
Mercedes-Benz CLA Alternator: Warning Signs, DIY Difficulty & Aftermarket Advice
These are the same regardless of make or model — see our full Alternator Guide for symptoms to watch for (plus a genuinely useful two-minute test to confirm it's not the battery instead), confirming the right amperage and fitment against your VIN, and which brands are worth trusting.
More Mercedes-Benz Alternator
The same part, covered across other Mercedes-Benz models.