W123/W126 diesel ignition lock defective? Replace the steering lock
Short answer: If the ignition key on the Mercedes W123 or W126 diesel can only be turned with force, spins freely, or the ignition stays dead, the steering lock is usually worn – the lock cylinder at the front, the ignition-starter switch at the back. Solution: replacement with a function-tested genuine steering lock, part number A1234622830, with key, for 219,00 € (diesel version, 0160-family housing marking).
The fault announces itself over months: the key goes into the lock more stiffly, you jiggle the steering wheel briefly, the car glow-plugs and runs. Eventually only wiggling it in a certain position helps – then it gets stuck, usually on a cold morning far from home. On the 123 and the 126 diesel, the mechanical and electrical parts sit in the same housing, and engine shutoff is tied to the key as well. That's exactly why the fault is often looked for in the wrong place.
Genuine steering lock for the diesel models of the 123 and 126 series – function-tested, with matching key.
Symptoms
| Symptom | Likely cause |
|---|---|
| Key can only be turned with force or not at all anymore | Worn tumblers in the lock cylinder, resinified lubricant |
| Key turns freely without resistance, nothing happens | Connection between the lock cylinder and the ignition/starter switch broken |
| Glow-plug warning light stays dark, the starter motor doesn't respond | Burnt-out contacts in the ignition-starter switch (terminal 15 or 50) |
| Steering stays locked even though the key turns | Jammed locking pin in the steering lock housing, common with the wheels turned |
| Engine keeps running after the key is removed | Not necessarily the lock: on the diesel, first check the vacuum lines and shutoff element – see step 4 |
| Ignition completely normal, only the doors can no longer be unlocked | Not the ignition lock: then it's the turn of the door lock cylinder or central locking – the approach is shown in W124 door lock defective |
| Your vehicle is a 190 or a 124 | Different design: for that, W124/W201 ignition lock defective the matching guide |
Causes
The steering lock of the 123 and 126 series combines several functions in one die-cast housing that age differently. At the front sits the lock cylinder with spring-loaded tumblers, behind it the locking pin that extends when the key is removed and locks the steering spindle. At the rear end, the ignition-starter switch is bolted on – permanent positive (terminal 30), operating voltage (terminal 15), and the starter's control current (terminal 50) all run through it.
After four decades, the tumblers and the key bit have worn each other down, the springs have fatigued, and the old grease has resinified into a dust-binding paste. A shot of penetrating oil buys a few months, no more. In parallel, the ignition-starter switch ages electrically: its contacts carry the control current at every start, and on the diesel the glow-plug system adds to the load. Eventually it no longer switches through under load – the warning lights come on, the starter stays silent.
Testing it yourself
- Test the spare key – costs nothing and clarifies the most. If the lock runs noticeably more easily with the rarely used spare key, it's mainly your everyday key that's worn. If it stays equally stiff, the wear sits in the cylinder.
- Relieve the steering wheel – move the steering wheel gently back and forth while turning the key. If it then works, only the locking pin is jamming under preload – the most common false alarm with the wheels turned.
- Separate the mechanics from the electrics – if the key turns cleanly through all positions without the glow-plug indicator or starter motor responding, the fault lies in the electrical part. If it catches, it's the mechanics. This observation saves the most searching.
- If the engine runs on, check the vacuum side – if the engine keeps running after being switched off, trace the vacuum path to the shutoff element: porous or slipped-off lines are the cheaper candidates. Only once this side is airtight does the lock come under suspicion.
- Check the connector and contact pins – under the steering column trim, pull off the connector at the ignition-starter switch: bent, tarnished, or scorched pins explain intermittent faults that would otherwise be blamed on the lock cylinder.
Solution
A worn-out lock cylinder cannot be adjusted, and a burnt-out ignition-starter switch cannot be sensibly repaired on the vehicle. The clean solution is replacement with a tested genuine part: Ignition lock with steering lock, part number A1234622830, for 219,00 €. The function has been personally tested, and the matching key is included. The housing bears the 0160-family marking – compare it with your old part before buying, that's the most reliable identification.
Two points before installation. First: the lock has its own keying of its own – the included key does not open the doors, glovebox or trunk lid; anyone who wants a single matching key set should transfer the cylinder from the old part. Second: what is stated is the diesel version for W123 and W126 – if your vehicle doesn't clearly fit this profile, clarify the fitment in advance. The lock is fitted on the steering column tube under the steering column trim. More genuine parts: W123, W126, Locks & door handles.
The matching replacement part – buy it directly from us
Mercedes ignition lock steering lock W123 W126 diesel with key
Part number A1234622830 · genuine Mercedes-Benz · function-tested, with key
219,00 €
Compatible vehicles
The overview shows the documented fitment for this lock – the diesel version is stated:
| Model series | Body style | Engine | Models according to product data |
|---|---|---|---|
| W123 | Sedan | Diesel | 200 D, 240 D, 300 D |
| S123 | T-model (estate) | Diesel | Diesel models of the series |
| W126 | Sedan | Diesel | Diesel models of the series |
Not to be confused with: For the W201 and the 124 series, this is not the correct design – there, the version described in the guide W124/W201 ignition lock defective fits. This item is not stated for petrol models of the 123 and 126 series. Unsure? Send the VIN and model year via our contact form – we'll check the fitment free of charge.
FAQ
Can I keep using my current car key?
Not without conversion. The lock has its own key set, and the matching key is included – however, it does not open the doors, glovebox or trunk lid. Anyone who wants to keep one key for everything should transfer the cylinder from the old part.
How do I tell whether the lock cylinder or the ignition/starter switch is defective?
If the key catches or jams mechanically, the lock cylinder is worn. If, on the other hand, it turns cleanly through all positions without the glow-plug indicator or starter motor responding, the fault sits in the ignition-starter switch at the rear end of the housing.
My diesel keeps running after I remove the key – is the ignition lock to blame?
Not necessarily. On the diesel, shutoff runs via the vacuum circuit. First check the vacuum lines and shutoff element for leaks – only once this side is airtight does the lock come under suspicion.
Does the lock also fit a W123 or W126 petrol model?
This item is not stated for that: the diesel version for W123 and W126 is specified. If in doubt, compare the 0160-family housing marking and the connector pinout with your old part, or ask in advance with the VIN.
What does the steering lock cost, and is it available?
The tested genuine steering lock A1234622830 costs 219,00 Euro. One unit with matching key is currently in stock – if the product page shows sold out, a quick inquiry is worthwhile.
More reading: W124/W201 ignition lock defective? Check & replace the steering lock – the guide for the 190 and 124 models.
KFZTeile-Thot is a specialist shop for tested and refurbished Mercedes parts with our own test benches and has over 1,000 positive eBay reviews. We have ignition locks, lock cylinders and many more genuine parts for W123 and W126 tested and in stock. Questions about fitment? Call us: 0179 8991069 (Mon–Fri 8 am–6 pm) – or use our contact form.