It's one of the most universal car problems in the UK. You walk up to your car, press the unlock button, and... nothing. No flash of indicators, no chunky thunk of the doors unlocking, no welcome chime. The fob in your hand suddenly feels useless.
Before you start panicking, calling a dealer, or assuming you need a brand-new key — work through this list. At least one of these 7 fixes solves about 80% of "fob not working" problems we get called about. None of them require special tools or a locksmith. Spend 5-10 minutes here before spending hundreds on a replacement.
Before working through the fixes, identify which symptom matches yours:
Most fixes below help most situations, but the most likely cause varies by symptom:
Now the fixes — in order of likelihood, easiest first.
This is by far the most common cause. Car key fob batteries last 2-4 years in typical use. When they die, the symptoms can be subtle: shorter range, intermittent unlocking, slow response — before failing completely.
How to check:
Most car keys use a CR2032 battery (a flat coin-shaped lithium battery, about the size of a 10p coin). Some larger fobs use CR2025 or CR2450. The battery type is usually printed inside the fob or on the existing battery.
How to replace:
If the fob has a separate emergency key inside (a small physical key blade), pull that out first — the fob often won't open while the emergency key is locked in place.
Important: if the fob has been used for a while with a very weak battery, occasionally the car loses its "memory" of the fob. In that case you may need Fix #5 (re-pair the fob) — but try Fix #1 first.
Most modern car key fobs include a physical emergency key blade hidden inside. This lets you unlock the door manually if the fob fails completely.
How to find it:
Why this matters now:
Even if your fob is completely dead, you can still:
This isn't a permanent fix, but it gets you mobile while you sort out the underlying problem. Read your car's manual for the "dead key fob" procedure — almost every modern car has one.
If the fob unlocks the doors but the engine won't start when you turn the key (or press the start button), the issue probably isn't the fob — it's the immobiliser.
The immobiliser is a separate security system that reads a chip inside the key. Even if the fob's remote functions work perfectly, a problem with the immobiliser chip (or its communication with the car) will stop the engine starting.
Common immobiliser issues:
For Mercedes drivers in particular, there's a specific problem called EIS (Electronic Ignition Switch) failure that mimics a "dead key" but is actually the car's ignition module. We've written a detailed Mercedes EIS guide if your symptoms match — common on W203, W211, W212, W221 models.
If Fix #1 (battery) and Fix #2 (emergency key) haven't worked AND the engine won't start, it's worth getting professional diagnosis. Continuing to force a non-working key can damage the lock cylinder.
Modern key fobs use radio signals (typically 433 MHz or 315 MHz in the UK). Sometimes nearby electronics block or interfere with that signal:
Quick test:
Walk to a different location with the car. If your fob is in a Faraday pouch (recommended security practice, but a common cause of "broken fob" calls), take it out. Try unlocking from 1-2 metres away rather than across the car park.
If interference is the problem, the fix is usually obvious once you've identified the source. Sometimes it's worth investing in a wired-button keyless entry — but that's a separate conversation.
This is more technical but still DIY-able for some cars.
If the fob's battery is fresh, the fob is undamaged, and there's no interference — sometimes the fob has simply lost its memory of being paired with the car. This can happen after a flat battery (Fix #1), after a software update at a dealer, or sometimes for no obvious reason.
Re-pairing varies by car make:
Important caveat: the specific procedure varies enormously by year, model, and country. Search YouTube for "[your car make] [model] [year] re-pair key fob" for visual instructions. If you've tried 2-3 attempts without success, stop — you can sometimes lock yourself out of the system entirely.
If the fob has been:
How to inspect:
Quick fixes:
If the fob is physically damaged beyond simple cleaning, you'll need a fob shell replacement (much cheaper than a new programmed key) or a full new fob.
Often overlooked. If you have a spare key — try it.
If the spare works perfectly: the original fob is the problem. You have time to fix it without urgency.
If the spare also doesn't work: the problem is the car, not the fob. This points to:
If neither key works, check the car battery first. A weak car battery (not the fob battery) can mimic "fob failure" symptoms exactly. If your car has been parked unused for a few weeks, this is a very common cause.
After working through these 7 fixes, you have two scenarios:
Scenario A: One of these worked — congratulations, you've saved yourself £50-£300. Order a spare fob if you don't have one already, and consider replacing the battery yearly as preventative maintenance.
Scenario B: Nothing worked — at this point you've ruled out the easy fixes. The likely causes now are:
At this point a mobile auto locksmith is your best option. They can diagnose the exact problem on-site, fix it without towing your car anywhere, and almost always for less than a main dealer charges.
We cover Greater London, Kent, Essex, Surrey, and Sussex. Most fob jobs include:
Our technicians use dealer-grade programming equipment and carry common fob blanks for most major makes. Most jobs are completed at your location in 30-60 minutes.
For prices and specific vehicle quotes, see our pricing page or call 07777 676261 for a quick phone diagnostic.
The single best thing you can do to prevent future fob problems:
My fob worked yesterday and stopped today. What happened? 99% of the time, this is the battery. The previous days, you were getting reduced signal — but today the battery hit too low to function at all. Replace and retest.
Can I program a new fob myself? For older cars (pre-2010) and certain models, sometimes yes — the procedures in Fix #5 work. For modern cars, programming usually requires dealer-grade equipment. Buy a fob blank online, then have a locksmith program it for £40-£80.
Why does the fob work close to the car but not from a distance? Almost always a weakening battery. The fob's transmission strength drops as battery voltage drops. Replace the battery (Fix #1) and range typically returns to normal.
My car still starts with the key in the ignition but the fob doesn't work. Is this OK? Yes — your immobiliser is working (Fix #3 confirmed), but your remote functions aren't. Most likely Fix #1 (battery) or Fix #6 (physical damage). Drive normally and fix the fob when you have time.
Can a locksmith fix a wet fob? Often yes — if the fob hasn't been wet for too long. Bring it in straight after drying. If it's been wet and sitting for days, the corrosion usually means a new fob is needed.
Worked through all 7 fixes and your fob still isn't cooperating?
Call 07777 676261 for a quick phone diagnostic — we can often identify the problem in 2-3 minutes and quote you accurately before sending a technician. Or WhatsApp us on +44 7777 676261.
For non-urgent fob issues or to order a spare while you still have a working one, use our contact form.
For more on related problems, see:
Most fob problems have simple fixes. Try the easy ones first.