Mercedes-Benz B1A5B13: Keyless Go Antenna Fault (Key Not Detected)
Mercedes code B1A5B13 means the Keyless Go control unit detects a fault in one keyless antenna circuit, so the car stops sensing the key in that zone. The car stays fully safe to drive, and the usual fix is a replacement antenna module.
Quick facts
- System
- Body / Keyless Go
- Severity
- Low
- Can you still drive?
- Yes, safe to drive
- Applies to
- W212 E-Class, C207 E-Coupe, W204 C-Class, R172 SLK with Keyless Go
Also shown by some scanners as: B1A5B, B1A5B-13, B1A5013, B1A4F13, B1A4A13, B1A4B13, B1A4C13, B1A4D13, B1A4E13, B1A5113
Symptoms
- Key not detected message even with the key inside the car
- Keyless entry works on some doors but not others
- Push-button start only works with the key held at the marked spot or in the slot
- Problem comes and goes, often worse after rain or a car wash
Common causes, most likely first
- 1
Aged or failed Keyless Go antenna or door handle sensor
On several chassis this exact code points at the passenger side door handle sensor circuit; bumper antennas fail from water entry over the years.
- 2
Wiring or connector fault to that antenna
- 3
Weak key battery (check this first, it costs a few ringgit)
- 4
Rarely, the Keyless Go control unit itself
Related parts and used prices
| Part | Used price range |
|---|---|
| Keyless Go antenna module A2128200989 (used, tested) | RM550 |
| Keyless entry module A2129005422 (W212, used, tested) | RM450 |
Prices shown are reference prices at the time of writing. Used part prices change with stock and condition; WhatsApp us for today's price.
In stock now at M.S. Motor
Not sure what is wrong? Book an inspection.
WhatsApp us your fault code and car model to book a time. We scan the car, confirm the actual fault, and quote the used part and labour before any work starts. All parts tested, with warranty.
Frequently asked questions
Is it safe to keep driving with B1A5B13?
Yes. Keyless Go is a comfort system; engine, brakes and safety systems are not affected. Use the backup start method in the meantime and repair when convenient.
Which antenna is the faulty one?
Not every sibling code is an antenna. B1A4E13 and B1A4F13 are the left and right LF antennas, but B1A4A13 and B1A4D13 point at the door handle sensor at a corner of the car, and the right fix there is the complete handle with its sensor, not an antenna module. A proper diagnostic scan shows which one your car stored. WhatsApp us your scan report and we help you confirm the correct part.
Will a used antenna module plug and play?
On these chassis the antenna module is normally plug and play with no coding needed. Match the part number, for example A2128200989 on the W212, and it works.
Why does it act up after rain?
Bumper antennas sit low and slowly absorb water over the years; moisture corrodes the coil and the fault turns intermittent. That is why the problem often appears after rain or a car wash.
What do the other B1A4x codes mean, like B1A4A13 or B1A4E13?
On W204, W212 and C218 era cars the block reads like this: B1A4A is the left front door handle sensor and B1A4D the right rear, B1A4E is the left LF antenna and B1A4F the right, while B1A4B and B1A4C are the other two handle-sensor corners whose exact positions Mercedes documentation does not confirm. B1A50 and B1A51 are further LF antenna circuits: a factory bulletin documents B1A51 as the rear antenna, and B1A50 is reported as the front left on the W176, though antenna positions are not guaranteed identical on every chassis. The last two digits are the failure type: 13 means open circuit, 12 means short to positive. Handle sensor codes are fixed with the complete handle including its sensor; antenna codes with the antenna. Note the left/right wording in Mercedes fault text is written for left-hand-drive cars, so on a Malaysian right-hand-drive car check which physical side the scan means. On newer W177 and W167 cars the same faults are worded differently and stored in the EZS, so there the scan text itself names the side. WhatsApp us the exact code and your model, we match the correct used part.