Why does my BMW X5 45e say 'Drivetrain malfunction'?

Short answer: On the X5 45e this warning is most often a failing 12V battery, especially the small auxiliary one. Owners paid about $300-$700 for the aux battery and up to $1,600 for both at a dealer. Test or replace the batteries before letting a shop replace the starter, and register the new battery with a scan tool.

Symptom: A yellow 'Drivetrain malfunction' or 'Driving still possible: Drivetrain' warning appears, often when the engine starts. The app may say the starter battery will fail soon, and the car may briefly go into limp mode or not start.

What to check first

1. Have both 12V batteries tested, including the auxiliary battery.
2. Try the owner-suggested test: open the hood and start the car. A click with no start points to the aux battery (confirm with a shop).
3. Read the stored codes before agreeing to a starter replacement.
4. Ask the shop to check ground wires.
5. Make sure any new battery is registered to the car.
6. Run your VIN at nhtsa.gov/recalls.

Likely causes

1. Auxiliary 12V battery failing. The 45e has two 12V batteries, a main one and a smaller auxiliary one. Several owners said a bad auxiliary battery set off Drivetrain malfunction, and that when it goes the main battery can be damaged quickly too. The 12V battery is the small battery that powers the computers, locks and screens.
2. Main 12V battery. Owners said the 45e 'eats' 12V batteries, and one had two pairs replaced in five years.
3. Starter motor. One owner's shop replaced the starter first without fixing it. Another dealer replaced the starter and then found both batteries bad.
4. Ground wire. One 2023 owner's warning was traced to a grounding wire.

What it usually costs

Owners reported about $300-$350 for an auxiliary battery at independent shops, about $700 at a dealer, about $250-260 for the part alone, and $1,500-$1,600 for both batteries at a dealer. A 12V battery may not be covered by warranty.

Is it safe to keep driving?

Owners said the car usually still drives, but it may go into limp mode or fail to start. Get it checked soon. If it loses power in traffic, pull over safely.

DIY or shop?

Replacing 12V batteries is a DIY job if you can register the battery with a BMW-capable scan tool. Starter and high-voltage work is for a shop.

Recalls, bulletins and complaints in plain words

• Related recalls: NHTSA lists 20V490000 and 20V601000 (2021 X5 xDrive45e among other BMW plug-ins: high-voltage battery cells may short from loose weld beads or debris) and 22V820000 (2023 X5 including the 45e: windshield bonding). None are about the 12V battery. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect. NHTSA files the 45e under the X5, so this count covers the whole X5 line.
• NHTSA complaints: 62 keyword-matched complaints for BMW X5 (all, including xDrive45e) 2021–2023 (of 217 unique complaints queried, NHTSA complaints API by model year, queried 2026-11-03; keywords: drivetrain, 12 v, battery, starter, won t start). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 2022 X5 45E Drivetrain malfunction warning on Reddit r/BMWX5, a 2022 X5 45e owner got Drivetrain malfunction after a low-fuel warning. Replies: one 2023 owner's was the auxiliary battery at about $300, another's was a ground wire. A commenter suggested a test: with the hood open, start the car. If it just clicks, the aux battery has failed.
• In 2023 x5 45e check drivetrain light. on Reddit r/BMWX5, a 2023 X5 45e owner's check drivetrain light came on when the car switched to the gas engine, once with brief limp mode. The shop replaced the starter, which didn't fix it, then the auxiliary battery, which did. It cost about $350, not the $1,100 the dealer first quoted.
• In 45e Bad Batteries + Starter on Reddit r/BMWX5, a 45e owner got 'Driving still possible: Drivetrain'. The dealer replaced the starter under warranty, then said both batteries were bad. Owners reported $1,600 for both batteries at a dealer, and about $700 for the auxiliary alone on a 2023 just out of warranty at 50,250 miles (goodwill declined, 10% discount given), and about $250-260 for the aux battery part. One said a replaced battery must be registered with a scan tool.
• In 72 plate X5 45e starter battery on Reddit r/BMWX5, a UK owner of a 2022 X5 45e saw a 'starter battery likely to fail soon' warning after about 1,000 miles of ownership. BMW's warranty didn't cover the 12V battery. One reply noted that many used 45es were almost never plugged in by earlier owners.

Quick tip

Batteries first, starter second. The aux battery is the usual culprit and is much cheaper.

Vehicle focus: BMW X5 xDrive45e plug-in hybrid (G05), 2021-2023.

Safety / mechanic note

Limp mode can leave you short on power. A plug-in hybrid's high-voltage system can stay live with the car off. Leave the orange cables and the big battery to a trained technician. Verify with a mechanic.