Home Maintenance Pre-purchase inspection

Smart Fortwo and Forfour 453 EQ Pre-Purchase Inspection — Electric Buyer's Checklist

Easy 60-90 min Smart Fortwo EQSmart Forfour EQ

Service interval: Run through this list before money changes hands; not after

What this is + why it matters

This is a buyer's checklist for a 453 EQ — the electric Smart Fortwo and Forfour built from roughly 2017 through 2024. It's a companion to the main pre-purchase inspection, not a replacement. Skip the engine items there; they don't apply. What does apply is a different set of checks centred on one variable: the high-voltage battery.

Be honest with yourself about what an EQ is. Factory range is 58-100 miles depending on year and trim. There is no DC fast charge — these cars are AC-only (Type 2 in Europe, J1772 in North America). And the high-voltage pack is, for practical purposes, not replaceable. Mercedes will not service the HV battery on an EQ out of warranty in most regions, and third-party rebuilds run more than half the value of the car. A degraded pack on a discounted EQ isn't a deal — it's a paperweight with seats.

That's the dominant variable. Everything else in this checklist is secondary.

What you'll need

A proper EV-capable OBD-II scanner, or a budget for a Mercedes dealer state-of-health (SOH) report. Most basic OBD scanners cannot read battery SOH on EVs — they'll show you a charge percentage, but not how much capacity that 100% represents anymore. Without an SOH read, you are flying blind on the most important number on the car.

A test drive long enough for the dash range estimate to settle — at least ten minutes of mixed driving. A flashlight for the underbody. And a willingness to ask the seller for charging history: where it was charged, how often it sat at 100%, whether it was kept plugged in.

If a seller refuses a dealer SOH read or won't allow a pre-purchase inspection at a Mercedes service centre, that is itself the answer. Walk.

Step by step

  1. Battery state of health (SOH). This is the number that matters. Mercedes dealers can read it directly off Xentry; some third-party EV scanners can pull it as well. Ask the seller for a recent SOH report, or pay for one yourself before money changes hands. Without an SOH read, you cannot price the car honestly. Rough guide: 75-80% on a 5-7 year old EQ is normal-good. 60% is poor. Below that and you're buying a paperweight.

  2. Range projection on a full charge. Charge to 100% (or as close as the seller is willing to let you), then look at the dash range estimate. Compare to factory spec for that year and trim. A 2018 Fortwo EQ that shows 35 miles at full charge against a 58-mile factory rating is telling you the pack has lost a meaningful chunk of capacity. The dash estimate is influenced by recent driving style, but the pattern across 10+ minutes of mixed driving is what you're reading.

  3. 12V auxiliary battery age. The EQ's small 12V aux supports the contactors and the battery management system. When the 12V dies, the HV pack won't deliver power and the car won't start — even with a full charge sitting under the floor. Check the aux battery date code. Anything over 4-5 years should be replaced immediately. The auxiliary battery 453 page covers the swap. This is the single most common "won't start" cause on the EQ, and it's a $200 fix — worth verifying before you walk away from a discounted car.

  4. Charging behaviour. Ask the seller to plug it in and let you watch a charge cycle start. Verify the car accepts the charge, holds the plug in the inlet, displays a sensible charge time, and that the dash and any companion app reflect the same state. Charging faults that show up only mid-cycle are the kind of thing that won't surface in a quick test drive.

  5. No DC fast charge — confirm the seller knows this. The EQ is AC-only. If the seller tells you "yeah, you can fast-charge it at any station" they are either misinformed or hiding something. Either way, you've learned something about the seller. Plan your ownership around 3-7 kW AC charging at home or work — anything else is a misunderstanding of the platform.

  6. HV warning lights and stored fault messages. Any high-voltage related warning on the dash — battery warning, charging warning, drive system warning — is a stop-the-deal flag until you understand what it means. Even if it's intermittent. Even if "it just comes on sometimes." Stored HV codes deserve a Mercedes-level scan before purchase.

  7. HV cooling system. The 453 EQ has a dedicated cooling loop for the high-voltage pack with an auxiliary water pump. Pack thermal management directly affects pack life — a cooling fault on an EQ is shortening your battery's remaining life every time you drive it. Check coolant level in the appropriate reservoir and look for any cooling-related stored codes.

  8. Standard 453 items. Tires (the EQ is heavier than the gas 453, tires wear faster). Brakes — regenerative braking does most of the slowing, so pads can corrode from disuse if regen alone hasn't been keeping them clean. A full set of body electronics — windows, lights, switches, infotainment. An OBD scan, even with a basic scanner, to pull stored body and chassis codes.

A note on the drivetrain: the EQ uses a single-speed reduction gear, not a DCT. It has none of the DCT-related concerns from the gas 453. There's no clutch, no gear-change software, no harsh-shift fault history to investigate. That entire category of 453 problems doesn't apply to the EQ.

Common gotchas

  • "Range estimate is just based on driving style." Partly true. But a degraded pack shows up as less reserve at the same drive style, and that's what you're reading for. Ten minutes of consistent driving and the estimate settles. The pattern across that window matters more than the absolute number.

  • Pack replacement is effectively unavailable. This is worth repeating because sellers will sometimes minimise it. Mercedes will not service an EQ HV pack out of warranty in most regions. Third-party rebuilds exist but cost more than half the car's market value. A bad pack means the car is at end-of-life economically, regardless of body and interior condition.

  • 12V aux failure is the #1 EQ no-start cause. Far more common than HV faults. If the seller is selling because "it suddenly won't start", the aux battery is the first suspect — that's a cheap fix and worth verifying before walking away from a discounted EQ. If the seller has already had the aux replaced and the car still won't start reliably, that's a different conversation.

  • Charging cable and adapters. Ask what's included. A 453 EQ without its original Type 2 / J1772 cable is a $300-500 cost to replace from scratch. Adapters for granny-charging at a normal household outlet are a separate item and not always included.

  • Time spent at 100% and time spent in heat degrades pack faster. A garaged car that was charged mostly to 80% and unplugged when not driving will hold up better than a daily driver kept always-plugged-in at 100% in a hot climate. Ask about charging habits — the answer tells you more than the odometer does.

  • "Brake pads are basically new" can mean two different things. Either the regen has been keeping them clean and they really are unworn, or the car has been sitting and the pads are corroded onto the rotors. Look at the rotor surface, not just the pad thickness.

When to skip DIY

The Mercedes dealer SOH report is the gold standard for this inspection, full stop. If the dealer is willing to do a paid pre-purchase inspection on the EQ — typically $150-250 in North America — that is money well spent on any car you're seriously considering. They have Xentry access, they can read pack-level data your scanner can't, and they'll catch HV-side issues no amount of test driving will surface.

If the seller refuses to allow a dealer pre-purchase inspection, or won't pay for an SOH read on a car they're asking real money for, that is the buying signal. Walk. There are enough EQs on the used market that you do not have to settle for one with hidden battery problems — and battery problems on this platform are not the kind of thing you fix later.

Manual references

Top reference manuals for this chassis (from our catalog of 88 Smart manuals):

Need something specific? Browse all 88 manuals by chassis, year, region, or document type.

Related maintenance