B152014 F2K5 Starter Relay Fault on Smart Fortwo 453

Typical Symptoms

• B152014 stored in a SAM scan (using iCarsoft, MB Star or equivalent)
• Intermittent no‑crank
• Starter that keeps engaging after the engine catches (relay welded closed)
• Sometimes accompanied by U‑codes from the same drive cycle
• Starter draws unusually high current at engagement

What it means

The 453 moves a lot of relay logic into modules rather than using plug‑in relays. F2K5 is the starter relay inside the F2 fuse and relay module. When the SAM reports B152014, it's saying that circuit has shorted to ground or the relay coil isn't responding. The catch is that F2K5 isn't a part you can pull and replace – it's integral to the module, and the module has to be paired to the car with Star Diagnosis when replaced.

Likely causes, cheapest first

1. Weak or failing main battery. Low voltage confuses the 453's sensitive electronics and throws phantom codes.
2. Weak or failing auxiliary battery. The 453 has a small secondary 12 V battery; if the main is fine, test this one.
3. Starter solenoid drawing too much current. An over‑current can weld the relay contacts closed; the SAM sees it as the same fault.
4. F2K5 relay or its driver inside the F2 module failed. Once battery and starter are ruled out, this is the dominant hardware cause.
5. Harness short to ground at the SAM connector. Rare; inspect for chafing where the harness passes through metal.

DIY check steps

1. Load‑test the main battery – many auto‑parts stores will do this for free. Replace if marginal.
2. Test the auxiliary 12 V battery if the main tests fine; one tired battery will throw codes from across the car.
3. Listen to the starter: a normal start has a click, spin and disengage. A stuck solenoid keeps the starter spinning; no click at all suggests the relay isn't being triggered.
4. Use a clamp meter on the battery cable while cranking if available. A draw well over 350 A means the starter is pulling too much current, pointing at the solenoid rather than the relay.
5. Stop here. Diagnosis and replacement of the F2 module require dash disassembly and Star Diagnosis adaptation; this isn't driveway work.

When to call a shop

This fault almost always ends up in a shop. The F2 module is buried behind dash trim and replacing it requires pairing with the SAM via Star Diagnosis. If a jump‑start makes intermittent no‑crank go away, the culprit is usually the battery, not the module. Don't pay to chase the hard fault until you've confirmed the battery is solid.

B00A068: Passenger Seat Occupant Sensor (OCS) B00A068 means the passenger seat's occupant classification system (OCS) isn't sending clean data. On the 453 the same problem triggers B00A068, B00A07B and B00A096 on different signal paths. These codes turn on the airbag light; treat them as one fault and address the connector under the seat first. Typical Symptoms • Airbag/SRS warning light on • Dash message like 'Malfunction – visit workshop' • B00A068 in a SAM scan, often with B00A07B and B00A096 • Light may go off briefly after a battery disconnect but returns What it Means The 453 uses a weight‑sensing mat in the passenger seat to decide whether to arm the passenger airbag. The OCS module reports on three signal paths, and any problem shows up as B00A068, B00A07B and B00A096. Don't chase them separately – it's one fault with three fingerprints. A bad OCS reading can cause the airbag to deploy when it shouldn't or not deploy when it should, so don't ignore it. Likely Causes (Cheapest First) Seat connector under the passenger seat unplugged or corroded – free to check. Slide the seat forward, lift the rear and inspect the multi‑pin plug for corrosion or looseness. Aftermarket seat cover interfering with the sensor mat – tight covers preload the mat and confuse the calibration. Wiring damage from a seat slide or a previous seat removal – harness can get pinched or stretched. OCS sensor mat in the seat cushion failed – less common. The mat is bonded into the cushion, so replacement requires removing the seat and separating the cushion. OCS control module failed – rare. The module sits behind the seat or in the floor depending on build year. DIY Check Steps Slide the passenger seat forward and lift the rear. Locate the connector pigtail under the seat. Inspect the connector. Push it firmly home until it clicks and look for green corrosion or moisture. Clean with electrical contact cleaner if needed. Disconnect the negative battery cable for 15 minutes, reconnect and see if the codes clear. If they come back, the harness side isn't the problem. Remove any aftermarket seat cover and clear the codes again. If they stay gone, the cover was interfering. Stop here. Anything beyond a connector reseat – such as replacing the sensor mat or module – requires Star Diagnosis and proper battery‑disconnect protocol to avoid airbag deployment. When to Call a Shop If a clean connector and reset don't fix it, the next step is professional. In some regions the Smart 453 airbag system is covered beyond the bumper‑to‑bumper warranty, so call the dealer with your VIN before paying out of pocket. A Smart‑experienced specialist can diagnose and replace the OCS mat or module safely.

B00A07B: Passenger Seat Occupant Sensor (Companion Code) B00A07B is one of three codes that the passenger‑seat OCS sets when it can't get a clean reading. It's the same fault as B00A068 and B00A096 reported on a different channel. Refer to the B00A068 guide for the full diagnostic flow; this section is the short version. Typical Symptoms • Airbag/SRS warning light on • Dash message about the passenger airbag or workshop visit • B00A07B in a SAM scan, almost always alongside B00A068 and B00A096 • Codes return after clearing unless the underlying issue is fixed What it Means B00A07B is the second of the three OCS fault codes. It's not a separate problem; the OCS module communicates over multiple paths and reports the same fault three ways. Read the B00A068 guide for detail; this section summarizes the key points. Likely Causes (Cheapest First) Seat connector under the passenger seat unplugged or corroded – most common. Aftermarket seat cover preloading the sensor mat – remove covers and re‑test. OCS control module failure – rare but becomes the suspect once the connector is ruled out. DIY Check Steps Inspect and reseat the passenger‑seat connector; slide the seat forward and push the plug firmly home. Clear codes with a scan tool or a 15‑minute battery disconnect. If all three codes return together, the fault hasn't been fixed. Remove any aftermarket seat cover and check again. Stop here; any further diagnosis requires Star Diagnosis and proper airbag handling. When to Call a Shop If the connector and a power cycle don't clear it, this is shop work. Airbag systems require proper equipment and battery‑disconnect procedures. In some regions Smart 453 SRS coverage is extended beyond the standard warranty – call the dealer before paying out of pocket.

B00A096: Passenger Seat Occupant Sensor (Companion Code) B00A096 is the third code in the 453 passenger‑seat OCS cluster. It's the same fault as B00A068 and B00A07B, just reported on a different signal channel. The diagnostic flow is identical: treat all three as one problem and start with the seat connector. Typical Symptoms • Airbag/SRS warning light on • Dash message about the passenger airbag or workshop visit • B00A096 in a SAM scan, usually with B00A068 and B00A07B • Codes return after clearing unless the connector or module is actually fixed What it Means B00A096 is the third of the three OCS codes. Each one is a different signal channel from the same control unit, so treat them as one fault. See the B00A068 guide for full details; this section gives the short version. Likely Causes (Cheapest First) Seat connector under the passenger seat loose or corroded – free to check and the most common cause. Aftermarket seat cover loading the OCS sensor mat – remove it and retest. Sensor mat or OCS module failure – rare but the suspect once connector and cover are ruled out. DIY Check Steps Reseat the connector under the passenger seat; slide the seat forward, lift the rear and push the plug until it clicks. Clear all three codes (B00A068, B00A07B, B00A096) and rescan after a key cycle. If they come back together, the fault isn't fixed. Remove any aftermarket seat cover and retest. Stop there without proper equipment. Airbag wiring is not a place to wing it. When to Call a Shop If a connector reseat and a new cap don't clear the code, it's shop territory. The Smart 453 may have extended SRS coverage – check with the dealer. A Smart‑experienced specialist is the next stop once warranty coverage is ruled out.

Related parts & typical prices

Part	Typical price	Search
Battery (453 main, AGM)	$140-220	Search Google
Auxiliary 12V battery (453, separate from main)	$40-90	Search Google
F2 vehicle interior fuse and relay module	$200-500	Search Google
Starter motor	$200-450	Search Google

Prices are rough community-reported ranges, not quotes. Aftermarket vs. genuine Mercedes parts swing the spread; call a Smart-experienced shop for an actual quote.

Manual references

• Service manual on Manualslib — external mirror (we don't host this specific document).
• Browse Smart manuals on smartcarmanuals.com — pick your chassis code section on the home page if a specific manual isn't listed above.

Community references

• Evilution: Specific error codes (B-code reference)
• FQ101: OBD code lookup