Engine Light On or Flashing
Steady means a fault is stored and the car is still managing. Flashing means a misfire is putting unburnt fuel into the catalytic converter, and the car should not be driven far.
Knocking or Ticking
A metallic knock that follows engine speed, or a tick that appears on start-up and fades. Both point at timing components, hydraulic lifters or bearing wear.
Smoke From the Exhaust
Blue is oil, white that does not clear is coolant, black is fuelling. The colour narrows the job before the car is even on the ramp.
Temperature Climbing in Traffic
A gauge that rises when the car stops moving points at the fan, the thermostat, a blocked cooling pack or a head gasket, and in this climate it escalates in days rather than months.
Losing Coolant With No Puddle
Coolant going somewhere invisible is either a pressurised leak that seals when cold or coolant being burnt, and the second one is not something to wait on.
Rough Idle or Hesitation
A cylinder not contributing, a boost or vacuum leak, or fuelling that has drifted. It reads as the car feeling flat before it reads as a fault.
Using Oil Between Services
Topping up more than once between services is a measurement worth taking properly, because some engines do it by design and some are telling you about their rings.
Power Loss or Limp Mode
The engine has protected itself from something it measured. It should be read before it is driven further, because limp mode is a symptom of a fault that is still there.