Symptoms — where to start diagnosing
Vehicle symptom catalog (rough idle, MPG drop, overheating, no-start, check engine) — with likely DTC codes and step-by-step OBD-II diagnostic plan.
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Engine misfires at idle
Rough idle, hunting RPM — how to start diagnosing and which OBD-II codes to check first.
P0300P0301P0302P0303P0304+3 -
Fuel consumption suddenly went up
MPG dropped 20-40%, no check-engine light — what to look at through OBD-II.
P0101P0130P0134P0135P0171+2 -
Car won't start (cranks but no fire)
Starter cranks fine, but the engine won't catch. What OBD-II shows and which codes to check.
P0335P0336P0340P0341P0230+2 -
Engine overheating
Temp gauge climbing into the red. What to monitor via OBD-II, which codes to watch.
P0116P0117P0118P0128P0217+1 -
Check engine light on (yellow) or blinking
The engine icon on the dash — what it means and whether you can keep driving.
P0300P0420P0442P0128P0171+1 -
Engine shakes on cold start
Engine vibrates the first 30-60 seconds after starting in cold weather — what it means and whether it's dangerous.
P0300P0171P0172P0507P0011+1 -
Automatic transmission slipping or harsh shifts
Transmission hangs between gears, RPMs climb but the car doesn't accelerate — symptoms and OBD-II codes.
P0700P0715P0717P0730P0740+2 -
ABS warning light on
Yellow ABS icon on dash — normal braking works fine, but anti-lock is disabled. How to diagnose via OBD-II.
C0035C0040C0045C0050C0110+2 -
Battery drains overnight (parasitic draw)
Car won't start in the morning — battery is flat. How to find the parasitic drain using OBD-II and a multimeter.
B1000B1001U0100U0101U0155+1 -
Oil pressure warning light on
Red oil can on the dash — one of the most dangerous dashboard warnings. What to do and OBD-II check.
P0520P0521P0522P0523P0524 -
Loss of power under acceleration
Car feels sluggish, throttle response is weak, passing feels impossible — possible causes and OBD codes.
P0299P0101P0171P0300P0234+2 -
White smoke from exhaust
Dense white (or bluish) smoke, especially after warm-up — a sign of coolant or water entering the combustion chamber.
P0217P0300P0172P0128P0401 -
Brake pedal vibrates when braking
Pedal pulsates or shudders when you press the brakes — causes and how to investigate with OBD-II and a scanner.
C0035C0040C0045C0050 -
Air conditioning not cooling
A/C blows warm or barely cool air — checking via OBD-II and spotting a refrigerant leak.
B1000P0532P0533P0534B1485 -
TPMS warning light on (tyre pressure)
Yellow exclamation tyre icon — low pressure or a faulty sensor. How to tell them apart.
C0750C0755C0760C0765C0775 -
Engine stalls while driving
Engine cuts out unexpectedly while moving — a dangerous symptom. First steps and OBD-II codes.
P0335P0340P0230P0627P0300+2 -
Car pulls to one side while driving
Steering doesn't hold center — let go and the car drifts. Causes range from alignment to uneven tyre pressure.
C0455C0460C0710C0800 -
Clicking or popping noise when turning
Clicking or crunching sound when turning the wheel — classic CV joint and tie rod symptoms.
C0035C0040C0045C0050C0110 -
High idle RPM (engine idles too fast)
Engine holds 1500-2000+ RPM instead of a normal 700-900 — causes and OBD-II PIDs to investigate.
P0507P0506P0505P0507P0171 -
Black smoke from exhaust
Black smoke = excess fuel. Causes range from a clogged air filter to faulty injectors.
P0172P0175P0101P2002P0088+1