Symptom
The vehicle uses noticeably more fuel than usual for the same driving. Often the only symptom of faults that otherwise feel harmless, and frequently the thing that finally prompts investigation.
Also described as: poor fuel economy, using more fuel, bad mpg, high fuel consumption, drinking fuel, worse economy, poor mpg, مصرف بنزین زیاد شد, مصرف سوخت بالا رفت, بنزین زیاد میخورد, gasta mas gasolina, gasta mucha gasolina, consume mucho combustible, mas consumo combustible, gasta mucha nafta, صرفية البنزين زادت, استهلاك وقود عالي, تشرب بنزين كثير, صرف البنزين كتير
38 of the 695 codes that produce this symptom indicate a fault where continuing to drive risks damage or is unsafe. If the symptom is sudden or severe, treat it as one of those until a scan says otherwise.
Establish that consumption has actually risen before diagnosing why, because more of these complaints are measurement than fault. A trip computer is a model rather than a meter and drifts after software updates or a battery change; brim-to-brim over several tankfuls on the same routes is the only figure worth reasoning from. Winter alone accounts for a large seasonal rise — longer warm-up, denser air, heated screens and seats, and short journeys where the engine never reaches temperature — so a complaint that arrived in November and nowhere else has probably answered itself.
Once a real rise is established, the mechanisms sort into three groups. The engine is being told to make a mixture richer than it needs: a lambda sensor reporting incorrectly is the classic, and French references put the resulting excess as high as 40 per cent, which is far more than most people expect from a single sensor. The engine never gets warm enough to leave its enrichment: a thermostat stuck open keeps the coolant below the temperature the management is waiting for, so it goes on enriching indefinitely — and the giveaway is a temperature gauge that reads low or takes an unusually long time to rise, with a heater that never gets properly hot.
Or the car is simply harder to move than it was, and this group is the one that gets skipped because it is not electronic. Under-inflated tyres are the largest single item: French sources put a 0.3 bar deficit at 3 to 5 per cent, which is more than most sensor faults. A binding brake, a dragging clutch, a seized wheel bearing and a roof rack left on since the summer all belong in the same list, and all cost nothing to check.
Read the fuel trims before condemning anything. They say directly whether the management is adding fuel or taking it away, and in which range — long-term trim well positive at idle and normal at cruise is a different fault from one positive everywhere.
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Consumption reported by the trip computer only, tank-to-tank figures normal | Measurement rather than fault — the computer is a model and drifts, notably after a software update or battery disconnection | Brim to brim over three tankfuls on comparable routes, and compare against the computer's figure for the same distance. | Nothing mechanical. Reset the computer's long-term average if the car offers it. |
| Arrived with cold weather, worst on short journeys | Normal seasonal rise — extended warm-up enrichment, denser air, and electrical heating loads | Compare the same route in the same conditions against last year rather than against summer. Check the engine actually reaches operating temperature on a typical journey. | No repair, unless the engine is not reaching temperature at all — which is the next row. |
| Temperature gauge reads low or rises very slowly, heater never gets hot | Thermostat stuck open — the engine never leaves warm-up enrichment | Watch live coolant temperature against the manufacturer's operating figure on a long run. A stable reading well below it is the finding. | Renew the thermostat. Consumption and heater performance recover together, which is itself confirmation. |
| Fuel trims sit well positive, or the exhaust smells rich | The management is adding fuel — a lagging or biased lambda sensor, a leaking injector, or excessive fuel pressure | Read short- and long-term trims at idle and at cruise separately; the pattern says where the error lives. Watch the upstream sensor switching — a lazy one crosses slowly rather than not at all. | Renew the sensor, injector or pressure regulator the readings name. Do not fit a lambda sensor on a code alone; it is often reporting a fault rather than being one. |
| Consumption rose with no driveability complaint at all | Rolling resistance rather than combustion — under-inflated tyres, a binding brake, or a roof rack still fitted | Check pressures cold against the placard. Feel each wheel after a drive: one noticeably hotter is a binding brake or a failing bearing. Coast in neutral on a level road and compare against how it used to feel. | Inflate to specification, free or renew the binding brake, remove the rack. These are the cheapest items on this page by a wide margin. |
| Air filter heavily fouled, or the service is long overdue | Restricted induction and degraded oil — the management compensates and burns more doing it | Inspect the filter against the light, and check the service interval and oil grade against the handbook. | Service it properly. This will not fix a large rise on its own and is the correct starting point regardless. |
| Diesel, with a particulate filter regenerating unusually often | Repeated regeneration burns fuel deliberately — the consumption is a symptom of the regeneration frequency, not of the engine | Read regeneration frequency and soot load. Regenerations every hundred kilometres rather than every several hundred is the pattern. | Diagnose why regenerations are frequent or incomplete — that is the actual fault, and consumption follows it. |
Consumption reported by the trip computer only, tank-to-tank figures normal
Arrived with cold weather, worst on short journeys
Temperature gauge reads low or rises very slowly, heater never gets hot
Fuel trims sit well positive, or the exhaust smells rich
Consumption rose with no driveability complaint at all
Air filter heavily fouled, or the service is long overdue
Diesel, with a particulate filter regenerating unusually often
Listed with the codes that most typically present this way first — the likeliest place to start.
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Fuel consumption is the most useful number a car gives you, and almost nobody writes it down. That is the whole argument of this article, and it is worth stating before anything el...
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