Fault codes

The one case where «buy a better adapter» is bad advice: a second, pricier adapter of the same kind will not see the car either. How to tell this from

A full sweep on a real car: two of twelve control units answer on the standard socket. Why that is not a fault, what you can still learn, and where «9

This takes ten seconds and should be done before buying a car: turn the key without starting. If the Check Engine light did not come on with the other

The car drives fine, fuel use is normal, nothing rattles — yet the check light is on and the emissions test fails. That is what a system working for o

The starter spins briskly, there is fuel, there should be a spark — and the engine will not catch. If a key or car-with-padlock symbol flashed on the

A penny sensor that can quietly ruin both starting and fuel consumption. It takes ten seconds and no tools to check — just compare two numbers in the

A code about an internal control unit fault sounds like a bill for thousands. In reality the culprit is usually not the unit but its power supply — an

Low-end pull has gone, the diesel started smoking and the idle turned rough — and there is an intake runner code on the list. Nine times out of ten th

You filled the tank and the needle did not move — or it drops in jumps. Usually a stuck float in the tank, but there is an unpleasant consequence peop

Cruise control stopped engaging, the speedometer froze or jumps, and the gearbox started shifting at the wrong moments. All of it is one sensor — or o

The car starts every other time, the battery lamp flickers, and the list shows voltage and alternator codes. Here is how to tell a dead battery from a

The dashboard shows «AdBlue» with a countdown in kilometres and the scanner returns a urea code. The countdown ends with the car refusing to start — a

These codes do not merely say «the mixture is wrong» — they say where and when: at idle or under revs, on bank one or bank two. That detail cuts the s

The fan runs non-stop, the air conditioning stopped switching on, or the car will not start — and the list shows relay codes. Almost always this is a

Pedal to the floor and the car barely moves, refusing to go past two thousand rpm. That is what electronic throttle protection looks like — and nine t

Everything lit up at once — check, ABS, stability — and the scanner returned codes starting with U. This is almost never fried electronics: usually a

The red oil can lit up, or the scanner returned P0521 — and you have a second to decide whether the sensor is lying or the engine really has no pressu

The automatic started jerking, hesitating before shifts or «slipping» on the motorway — and the scanner shows P0700. Here is what stands behind it and

The car has lost power, or jerks under acceleration. What a scanner shows here — and what you still have to check by hand.

Lost power, higher fuel use, and a quieter engine under load? That is what a car looks like when it can no longer hear knock.

The unit uses it to judge how much air enters the engine. It lies quietly: the car drives, but fuel use rises and power fades.

The code names the cylinder — and that is half the job done. How to tell a dead injector from a broken wire without removing anything.

The car jerks pulling away, the revs live their own life, the pedal answers late. One reading on screen tells whether the throttle is to blame.

The car jerks under load and dies on a climb. How to tell a tired pump from a blocked filter and from the sensor simply lying.

P0420 is not a death sentence. What kills a catalyst, how to tell a dead one from a wrongly blamed one, and what actually follows a «delete».

The decision is made in a minute at the roadside. In order: what means stop now, what means you can get home, and what means nothing happened at all.

Fitted LPG and the light came on. Usually the engine is not broken — the two systems are not agreeing. Which codes are expected and which are not.

The buyer will turn up with a cheap adapter. Better to know in advance what they will see — and why clearing codes before a sale is pointless.

A fault that comes with the weather is not a mystery but a hint. It names the place to look.

The part was replaced, the code cleared, and a week later the light is on again. Five causes in order of frequency, and how to tell them apart.

A code that can stall the engine on the move and refuse to start a minute later. Where to begin, and why the part is not first.

The ABS light is on, and the app says «no faults». The tool is not broken — it is looking elsewhere, and here is why.

P0171, C0035, U0100 — five characters, and each says something. Once you can read them, an unfamiliar code makes sense without a reference.

Three words next to the code. They decide whether to go to a garage today or simply keep an eye on it.

The engine dies at speed and the steering and brakes go heavy at once. Safety first, causes second.

The needle is climbing. The next five minutes decide whether this costs a thermostat or a cylinder head.

The diesel got sluggish, consumption is up, the fan roars when parked. Here is what is happening and how to help.

Along with the code the car stores the conditions it was recorded under. That is what tells a one-off from a permanent fault.

The revs will not climb, the pedal does nothing, the speed hits a ceiling. That is not a broken gearbox — it is protection.

The code sounds worse than it is in half the cases. But it must be checked before you drive on.

Insufficient recirculation flow. In most cases that is soot, not a dead part.

The engine never reaches operating temperature. The part is cheap, but replacing it blind is still a bad idea.

A steady lamp means «look into it soon». A blinking one means «stop». Two different messages, and the difference is expensive.

A mass air flow sensor lies gradually. The car still drives, just worse — and the numbers show it before you feel it.

The sensor rarely dies outright. Far more often it answers slowly — and live data shows it.

The button turns the lamp off; it does not fix the car. And it erases exactly what the mechanic needed.

Three codes whose culprit costs nothing in a third of cases and is fixed by hand in five seconds.

The one group of codes where «it can wait until the weekend» costs more than the repair itself.

The most expensive-looking code in the book. And the most common case of replacing a thousand-dollar part for nothing.

«System too lean» is the most common entry in the engine memory. The cause is almost never the part people suspect first.