MG Comet & Windsor EV Motor Problems: Diagnosis & Repair

The MG Comet EV and MG Windsor EV are two of the most popular electric cars from JSW MG Motor India, yet they sit at opposite ends of the EV spectrum. The Comet is a tiny city runabout built around a compact rear-mounted Permanent Magnet Synchronous Motor (PMSM) of roughly 31 kW (about 41 hp) feeding 110 Nm to the rear wheels. The Windsor is a far larger crossover with a 100 kW (134 bhp) front-mounted PMSM pushing 200 Nm to the front wheels through a single-speed reduction gear. Both depend on a high-voltage traction inverter (the motor controller) to convert DC battery power into the precise three-phase AC the motor needs.

Because an EV has no clutch, gearbox, or engine in the traditional sense, the motor and its controller are the heart of the car. When they misbehave, you feel it instantly: jerking, sudden power loss, a refusal to move, or a whining noise that was not there before. This guide explains the genuinely common motor and drivetrain complaints on the Comet and Windsor, what causes them, how a proper workshop diagnoses each fault, what is safe to check yourself, and realistic indicative repair costs in Indian rupees. If your car is currently struggling, you can also book an EV motor repair and have a technician look at it.

How the Comet and Windsor drivetrains actually work

Understanding the layout helps you reason about faults. On both cars the high-voltage battery sends DC power to a traction inverter. The inverter uses fast-switching power transistors (IGBTs or MOSFETs) to chop that DC into three-phase AC. A rotor-position sensor — a resolver or a set of Hall sensors — tells the controller exactly where the motor's rotor is at every instant, so it can time the current pulses to produce smooth torque. Temperature sensors in the windings and on the inverter let the system protect itself from overheating.

The MG Comet uses a small PMSM mounted at the rear axle, which is why it is rear-wheel drive despite being a city car. The MG Windsor uses a larger PMSM at the front, driving the front wheels through a single-speed automatic transmission. In both, "Drive" and "Reverse" are simply different current patterns commanded by software — there is no mechanical reverse gear. This is why so many "drivetrain" problems on modern EVs are actually electrical or software issues, not worn mechanical parts.

Both cars also use regenerative braking, where the motor runs as a generator to slow the car and recharge the battery. The Windsor is well known for its steering-mounted KERS paddles that let you choose how aggressive this regen is. When regen behaves oddly — surging, cutting out, or feeling jerky — the fault usually lives in the same controller and sensor chain that drives the motor.

Common motor and controller problems on the Comet and Windsor

Here are the symptoms owners actually report, and what each one typically points to.

Jerking or surging during acceleration

A smooth EV should pull cleanly from a stop. If your Comet or Windsor jerks, hesitates, or surges — especially at low speed or when easing on and off the accelerator — the controller is struggling to deliver smooth torque. The most common culprits are a degrading rotor-position sensor (resolver or Hall), a throttle/accelerator pedal position sensor sending noisy data, or a software calibration issue between the pedal map and the inverter. On the Windsor, owners sometimes confuse aggressive regen-on-lift with a fault; genuine jerking persists even with regen set low.

Sudden power loss and limp mode

Limp mode (often shown as a turtle icon, a "Reduced Power" message, or a warning lamp) is the car deliberately capping output to protect itself. The Comet and Windsor will drop into limp mode if the controller detects an inverter over-temperature, an over-current event, a position-sensor signal it cannot trust, a high-voltage interlock issue, or a serious battery/BMS fault upstream. It feels like the car suddenly will not accelerate past 20-40 km/h. This is a protective state, not random — there is almost always a stored fault code explaining why.

No drive at all — the car will not move

You press the accelerator and nothing happens, even though the car powers on. This is frightening but often points to a small number of causes: a failed high-voltage contactor not closing, a loss of the position-sensor signal, a blown HV fuse, a controller fault that has shut down the inverter, or a "Ready" interlock that is not being satisfied (for example a charging connector still detected as plugged in). Mechanical motor seizure is rare on these cars; an electrical or interlock fault is far more likely.

Whining, grinding, or droning noise

Some Comet owners report motor and drivetrain noise entering the cabin more than they expected. A faint electric whine that rises and falls with speed is normal for a PMSM. What is not normal is a new grinding, rumbling, or metallic droning — that usually means a failing motor or reduction-gear bearing, a problem with the gear mesh, or a loose mount. A high-pitched electronic whine that changes with load can also come from the inverter itself. Noise that worsens over weeks deserves attention before it turns into a bearing failure.

Overheating and derating on long or hot runs

In Indian summers, thermal management is a real-world stress. If the car noticeably loses performance after sustained highway running or repeated hard acceleration, the controller may be derating to protect the inverter or motor windings. Occasional, brief derating in extreme heat can be normal. Frequent derating at moderate effort suggests a cooling-system problem, a clogged radiator/coolant path, a failing coolant pump, or a temperature sensor reading high.

Regenerative braking surging or cutting out

Because regen uses the motor as a generator, regen faults share the same root causes as drive faults: position-sensor noise, controller faults, or — very commonly — the battery simply being too full or too cold to accept charge, in which case regen is reduced by design. If regen feels jerky or unpredictable across all states of charge, the controller and sensors are the place to look.

What actually causes these faults

Most Comet and Windsor motor complaints trace back to a short list of root causes.

• Controller / inverter faults. The inverter is the most failure-prone part of the drive system. Aged DC-link capacitors, a failed power-transistor (IGBT/MOSFET) leg, dry solder joints, or current-sensor drift all produce jerking, power loss, or a dead inverter. Inverter faults are also the most common reason for limp mode.

• Motor windings. A PMSM has three stator windings. Insulation breakdown, a phase-to-phase short, or a phase-to-ground fault causes rough running, power loss, or a hard shutdown. Winding faults often follow moisture ingress or long-term heat stress.

• Rotor-position sensor (resolver / Hall). If the controller cannot tell exactly where the rotor is, it cannot time the current correctly. The result is jerking, cogging, weak torque, or a no-start. A loose sensor connector or water in the plug can mimic a failed sensor.

• Bearings. Motor and reduction-gear bearings wear over time and with water exposure. Early signs are noise and vibration; late-stage failure can damage the rotor or gears.

• Water ingress and corrosion. India's monsoon and waterlogged roads are hard on EVs. Water in a high-voltage connector, the motor housing, or the inverter causes intermittent faults that come and go with weather — often the hardest faults to chase.

• Loose or corroded HV connectors. The orange high-voltage cables carry serious current. A connector that is loose, corroded, or not fully latched causes intermittent power loss, derating, or fault codes that appear over bumps.

• Software, throttle, and calibration. Many modern EV "drivetrain" complaints are fixed with a software update at the dealership. Pedal-map glitches, controller firmware bugs, and BMS-to-inverter communication errors are common, and JSW MG has issued software updates for charging and drive-related behaviour on these cars.

How a proper diagnosis works

Guessing is expensive on an EV. A correct diagnosis follows a logical, instrument-led sequence rather than swapping parts.

1. Read the fault codes over CAN. The technician connects a diagnostic scan tool to the OBD/diagnostic port and pulls stored Diagnostic Trouble Codes from the motor controller, BMS, and vehicle control unit. Codes point directly at inverter over-temperature, position-sensor faults, over-current events, phase faults, or interlock problems. This single step usually narrows the cause from "the motor is broken" to a specific subsystem.

1. Review live data. With the tool still connected, the technician watches real-time values: motor RPM, inverter and motor temperatures, phase currents, DC-link voltage, accelerator-pedal position, and the position-sensor signal. A sensor that drops out or reads implausibly is caught here.

1. Inspect HV connectors and wiring. Many intermittent faults are simply a loose, corroded, or water-contaminated orange connector. A visual and physical inspection (done safely, with the HV system isolated) catches these before any part is replaced.

1. Test the position sensor. The resolver or Hall sensors are checked for correct signal output and wiring continuity. A failed sensor or a bad plug is a relatively inexpensive fix compared with a motor swap.

1. Insulation and winding tests. If a winding fault is suspected, the motor windings are tested for insulation resistance to ground and for balance between the three phases. This confirms whether the motor itself is healthy or whether it has an internal short.

1. Bearing and mechanical check. For noise complaints, the technician listens for and feels bearing roughness, checks mounts, and inspects the reduction gear. This distinguishes a cheap bearing job from a costly motor replacement.

A good diagnosis tells you exactly which part is at fault and why — so you are not paying to replace a healthy motor when a sensor or connector was the real problem.

Safe DIY checks versus when to call a professional

Important high-voltage safety warning: the Comet and Windsor traction systems operate at voltages that can injure or kill. Never open the orange high-voltage cables, the inverter, the motor housing, or the battery casing. Do not probe HV connectors. Internal motor and controller work must only be done by trained EV technicians with the correct insulated tools, personal protective equipment, and a documented procedure to isolate and verify the HV system is de-energised.

Safe checks an owner can do:

• Note the exact symptom and when it happens. Cold start versus hot, over bumps, in rain, only above a certain speed — these patterns are gold for diagnosis.

• Read and photograph any dashboard warning. The turtle/limp icon, "Reduced Power", or a specific warning lamp tells the workshop a lot before you arrive.

• Try a clean restart. Fully power the car off, wait, and restart. A genuine transient sometimes clears; a fault that returns immediately needs a workshop.

• Check the obvious non-HV items. Confirm the 12V battery is healthy (a weak 12V battery causes many strange "won't go to Ready" faults), make sure no charging cable or warning is active, and check tyre condition for vibration complaints.

• Look (do not touch) for leaks or burning smells. Coolant on the floor or any burning smell means stop driving and call for help.

Call a professional immediately if you see limp mode that returns, any loss of drive, a burning smell, smoke, a coolant leak, a grinding noise, or any high-voltage warning. Do not keep driving a car that has dropped power — limp mode exists to prevent further damage. For anything beyond reading a warning light, book an EV motor repair and let a trained technician handle the high-voltage side safely.

Repair versus replace — and indicative INR costs

The good news: a full motor replacement is rarely the right answer. Most Comet and Windsor drive faults are fixed at the sensor, connector, software, or bearing level for a fraction of the cost of a new motor. The figures below are indicative ranges for the Indian market and vary by city, parts availability, and whether you use a dealer or an independent specialist. Always get a written diagnosis and quote first.

• Diagnostic scan and inspection: roughly Rs 800 to Rs 3,000. Often adjusted against the repair bill if you proceed.

• Software update / recalibration (drive, pedal, regen, charging behaviour): typically free under warranty at a JSW MG dealer; otherwise roughly Rs 1,000 to Rs 4,000 at an independent.

• HV connector clean-up, re-seat, or replacement, or harness repair: roughly Rs 2,000 to Rs 15,000 depending on which connector and whether parts are needed.

• Rotor-position sensor (resolver / Hall) replacement: roughly Rs 6,000 to Rs 25,000 including labour, depending on access and part.

• Motor or reduction-gear bearing replacement: roughly Rs 8,000 to Rs 30,000, depending on whether the motor must come out and be split.

• Inverter / controller repair (component-level, e.g. capacitors or a power module) where feasible: roughly Rs 15,000 to Rs 60,000. Specialist component-level repair is often far cheaper than a new controller.

• Inverter / controller replacement (new unit): roughly Rs 60,000 to Rs 1,80,000-plus, which is why diagnosis matters so much.

• Motor rewinding (if a winding fault is confirmed and rewinding is viable): roughly Rs 20,000 to Rs 70,000 for the winding work.

• Full traction motor replacement (assembly): typically Rs 1,50,000 and upward, and usually a last resort.

As a rule: replace cheap, high-failure parts (sensors, connectors, software) first; pursue component-level inverter repair before buying a new controller; and only consider a full motor swap when winding or mechanical damage is confirmed by testing. Many cars sent in for a "motor problem" leave after a sensor, connector, or software fix costing under Rs 25,000.

Warranty — what is covered and how to claim

Both cars carry strong EV-specific warranties, and the motor and controller are well covered, so do not pay out of pocket for something the manufacturer should fix.

For the MG Windsor EV, the standard package is a 3-year vehicle warranty (unlimited km for private use) covering manufacturing defects, with the traction motor and related powertrain electronics typically falling under an 8-year / 1,60,000 km cover. The high-voltage battery is offered with a lifetime, unlimited-km warranty for the first registered owner; on resale it reverts to the industry-standard 8 years / 1,60,000 km.

For the MG Comet EV, the vehicle warranty is commonly 3 years / 1,00,000 km, with the battery and powertrain covered up to 8 years / 1,20,000 km, and MG has promoted a lifetime battery warranty for the first owner that similarly reverts on transfer. Roadside assistance is bundled for the first few years.

These are indicative terms — exact coverage depends on your variant, your purchase date, and the warranty booklet you signed, so always confirm against your own documents and the latest JSW MG policy.

How to claim a motor or controller fault under warranty:

1. Report it early and stop driving if the car is in limp mode or has lost drive — continuing to drive can be treated as owner-induced damage.

1. Document everything. Photograph the warning lights, note dates, symptoms, and conditions, and keep your service history. A complete record makes approval smoother.

1. Go to an authorised JSW MG service centre. Warranty motor and inverter work must generally be done by the authorised network. Ask them to read the codes and put the diagnosis in writing.

1. Keep all paperwork — job cards, diagnosis, and replaced-part details — in case of any future dispute or resale.

1. If you are out of warranty or want an independent second opinion, an EV specialist can diagnose the fault and tell you whether it is a manufacturer defect worth pursuing or a wear item.

How ev.care helps

ev.care is India's dedicated EV repair and service brand, and motor and controller faults are exactly the kind of work we handle across any brand — including the MG Comet and Windsor. We start with a proper CAN-based diagnostic to read fault codes and live data, so you know the real cause before spending money. From there we can carry out rotor-position sensor and Hall/resolver replacement, HV connector and harness repair, motor and reduction-gear bearing replacement, insulation and winding testing, and component-level inverter diagnostics — escalating to a controller or motor replacement only when testing proves it is truly needed.

If your symptoms also involve charging — slow charging, charge faults, or a car that will not go to "Ready" — that often overlaps with drive faults, and our EV charging repair & service covers the charging side end to end. You can even run our free EV charging diagnostic tool first to narrow things down before you book. When you are ready, book an EV motor repair and we will diagnose the fault safely and quote transparently.

It also helps to understand how faults differ across brands and subsystems. If you own or are comparing other EVs, these guides are useful background: Tata Nexon EV charging problems, Ola S1 charging problems, and the deeper dive on EV battery and BMS faults and diagnostics, since a battery or BMS fault upstream is a frequent reason a healthy motor drops into limp mode.

Frequently asked questions

Why does my MG Comet or Windsor jerk when I accelerate?

Jerking usually means the controller is not delivering smooth torque, most often because of a noisy or failing rotor-position sensor, an accelerator-pedal sensor sending bad data, or a software calibration issue. On the Windsor, make sure it is not simply aggressive regen-on-lift, which is adjustable. Genuine jerking that persists with regen set low should be scanned for fault codes.

What does limp mode mean on my MG EV, and is it safe to keep driving?

Limp mode is the car deliberately limiting power to protect itself, usually shown as a turtle icon or a reduced-power message. It is triggered by faults like inverter over-temperature, over-current, a position-sensor problem, an HV interlock issue, or a battery/BMS fault. Drive only as far as you safely must, then stop and get it diagnosed — continuing to push a car in limp mode can cause further damage and may complicate a warranty claim.

My EV will not move at all even though it powers on — what is wrong?

A car that powers up but will not drive often has a high-voltage contactor that is not closing, a lost position-sensor signal, a blown HV fuse, a controller fault, or an interlock that is not satisfied (for example a charging connector still detected). Mechanical motor seizure is rare. This needs a workshop with a scan tool — do not attempt high-voltage diagnosis yourself.

Is the whining or grinding noise from my Comet or Windsor normal?

A faint electric whine that rises with speed is normal for a PMSM. A new grinding, rumbling, or metallic droning is not — it usually points to a failing motor or reduction-gear bearing, a gear issue, or a loose mount. Noise that gets worse over time should be checked early, before a bearing failure damages the motor or gears.

How much does it cost to fix a motor or controller fault in India?

It depends entirely on the root cause. A software fix is often free under warranty or roughly Rs 1,000 to Rs 4,000 otherwise; a position sensor is roughly Rs 6,000 to Rs 25,000; a bearing is roughly Rs 8,000 to Rs 30,000; component-level inverter repair is roughly Rs 15,000 to Rs 60,000; and a full motor or new controller can run from Rs 60,000 to well over Rs 1,50,000. This is exactly why a proper diagnosis first usually saves money — most "motor problems" are fixed at the sensor, connector, or software level.

Are the motor and controller covered under MG's warranty?

Yes. On the Windsor and Comet the traction motor and powertrain electronics typically fall under an 8-year warranty (1,60,000 km on the Windsor, 1,20,000 km on the Comet), with the battery covered even longer — a lifetime/unlimited-km cover for the first owner that reverts to the industry standard on resale. Report faults early, keep your service records, and have authorised service confirm the diagnosis in writing. Always verify the exact terms against your own warranty booklet and the latest JSW MG policy.