Driver's guide
Car systems: how they work and what fails
Each car system explained in plain words: what it is for, how it works, which faults are the most common, the symptoms they cause and the OBD codes that point to them. From here you reach the symptoms, questions and codes of each one.
Reviewed by Daniel Morales, founder of Reprorace SL, on
The systems, one by one
Pick a system to see how it works, what usually fails, which symptoms it gives and which codes point to it.
Engine and lubrication
How the engine, the valve timing and the oil circuit work, which faults are the most common, the symptoms they cause and the OBD codes that point to them.
Cooling
How the engine is cooled (water pump, thermostat, radiator and fan), which faults are the most common, the symptoms they cause and the OBD codes that show up.
Ignition
How ignition works (spark plugs and coils on gasoline engines, glow plugs on diesels), which faults are the most common, their symptoms and their OBD codes.
Fuel and air
How the engine meters air and fuel (mass air flow sensor, throttle, injectors and pump), which faults are the most common, their symptoms and their OBD codes.
Exhaust and emissions
How the oxygen sensor, the catalytic converter, the EGR, the particulate filter and DEF (AdBlue) work, the faults they cause, their symptoms and their OBD codes.
Turbo
How the turbocharger, its boost control and the intercooler work, which faults are the most common, the symptoms they cause and the OBD codes that show up.
Transmission
How the clutch, manual and automatic transmissions and the drivetrain work, which faults are the most common, the symptoms they cause and their OBD codes.
Brakes, ABS and ESC
How the brakes, ABS, electronic stability control (ESC) and the electric parking brake work, the faults they cause, their symptoms and their OBD codes.
Steering and suspension
How power steering, the suspension, the wheels and the tire pressure monitoring system work, the faults they cause, their symptoms and their OBD codes.
Electrical system and battery
How the battery, the alternator, the starter and the power supply of the control modules work, the faults they cause, their symptoms and their OBD codes.
CAN network and modules
How a car's control modules talk over CAN, what the gateway is, what U codes mean, which faults are the most common and how they are diagnosed.
Airbags and passive safety
How the airbags, the seat belt pretensioners and the belt sensors work, the faults they cause, what the airbag light means and the OBD codes that show up.
Keep reading
Car symptoms: what they mean and what to do
Warning lights, jerking, smoke, noises, smells or a car that won't start: what each symptom means, whether you can keep driving and what to check.
Car diagnostics: frequently asked questions
Clear answers to what drivers and repair shops ask about car diagnostics: OBD, trouble codes, inspections, O2 sensors, EGR, DPF, DEF (AdBlue) and the battery.
OBD fault codes: what each one means
Glossary of OBD-II/EOBD fault codes (P, C, B and U) in plain English: what each code means, common causes, severity and whether you can keep driving.
Vehicle diagnostics glossary
Nearly 50 vehicle diagnostics terms explained in a sentence or two: OBD, UDS, DTC, ISO-TP, DoIP, CAN FD, K-Line, J1939, DM1, J2534, D-PDU and more.
Check engine light on: what to do
Your engine warning light has come on: what it means, when to stop, when you can drive to a workshop and how to find out which code the car has stored.
Remote OBD diagnostics: what it is, how it works and what it can't do
What remote OBD diagnostics is, how it works with ECO-LITE, ECO-LITE TOOL and the platform, what can and can't be done remotely, and how the driver approves it.
See what your car is saying, system by system
The ECO-LITE plugs into the OBD port and shows the codes and live data your car publishes on your phone, explained; when needed, you share the session with your repair shop.
Presale price: €129 · US$129
Frequently asked questions
Which system is failing when the check engine light comes on?
The check engine light is turned on mostly by the engine, ignition, fuel and air, turbo, and exhaust and emissions systems: it is the warning of the emissions diagnostics. Brakes, airbags and the battery have their own warning lights.
Does an OBD reader see every system?
The generic part (OBD-II/EOBD) mostly covers what affects emissions. Brakes, airbags, body electronics and automatic transmissions use the manufacturer's own diagnostics, which not every reader can read.
How do I know which system a code belongs to?
The first letter gives the main group (P powertrain, C chassis, B body, U network) and the next characters the subsystem. Each code page links to the car system it belongs to.