Read the fault code before you buy the part: what the Wanchebao OBD reader at ¥121 can and cannot tell you
The warning light comes on, and the reflex is to start swapping parts until it goes out. An OBD2 reader interrupts exactly that: it plugs into the diagnostic socket your car already has and turns the light into a code you can look up. This Wanchebao unit is sold as a full-vehicle diagnostic decoder that works with a phone, and at 121 yuan it costs less than most of the parts you might otherwise replace on a guess. The routine is short: find the socket, usually under the dash within reach of the driver's seat, plug the reader in, turn the ignition to on without starting the engine, then connect the phone and read the stored codes. What a code gives you is the circuit or the system, not the broken component. A misfire on cylinder 1 can come from a plug, a coil or an injector, so clear the code, drive as usual and see whether it returns before ordering anything. The listing does not say which control modules it can reach, which app it pairs with, or whether a subscription is needed, so confirm those against your own model year first. Listed at 121 yuan against 136 yuan, with annual sales around 10,000 units.