Symptom
Loss of power
The engine produces less than it should — slower acceleration, struggling on hills, or needing more throttle for the same result. The most commonly reported symptom in the corpus, which also makes it the least specific on its own.
Also described as: no power, lacks power, won't pull, sluggish, gutless, underpowered, feels flat, down on power, poor acceleration, افت قدرت, ماشین قدرت ندارد, کشش ندارد, شتاب ندارد, perdida potencia, pierde potencia, no tiene fuerza, falta potencia, carro no jala, فقدان القوة, السيارة ضعيفة, ما فيها نفس, قوة المحرك ضعيفة, السيارة مش شايلة, سيارتي ضعيفة, عربيتي مش شايلة
Some causes mean you should stop driving
257 of the 844 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.
What this usually means
Ask first whether the power was taken away or whether it is not being made, because that single question splits an enormous list into two manageable ones and the driver can usually answer it.
A limit that is imposed goes away when the ignition is cycled. The management withdraws power to protect something or because it has stopped trusting a signal, and the withdrawal is latched until the next start — so a car that is flat until you stop, switch off and restart, then pulls normally, has an electronic limit rather than a mechanical failure. A mechanical fault does not repair itself in a car park. If it does not come back after a restart, the engine genuinely cannot make the power and the rest of this page applies.
An engine is an air pump, and everything that makes power scales with how much air it can move. So the mechanical population is a list of restrictions and leaks: a turbocharger not delivering boost, boost escaping through a split hose or a failed intercooler, an exhaust that cannot get rid of what has been burnt, a particulate filter loaded to the point of throttling the engine, or an air meter under-reading so the management supplies too little fuel for the air that is actually arriving.
On a turbocharged engine, resist the conclusion that the turbo has failed. German workshop references put the turbocharger itself as intact in the large majority of cases that arrive as boost faults — what is actually wrong is usually the variable geometry vanes coked solid with soot, the actuator or its vacuum supply, a split charge pipe, or a particulate filter that has choked the exhaust energy the turbo runs on. The turbo is what gets replaced and the vanes are what were stuck, which is an expensive way to be nearly right.
The exhaust side is the one most often missed entirely, because a partial restriction flows well enough at idle to look normal and only chokes at speed. It is measurable rather than a matter of opinion: backpressure under roughly 1.5 psi at idle and under about 3 psi at 2,000 rpm on most engines, with a comparison between the pre- and post-catalyst ports localising a melted converter.
Working through it
| What you find | Likely cause | How to confirm it | What fixes it |
|---|---|---|---|
| Power returns after switching off and restarting | An imposed limit rather than a mechanical failure — the management withdrew power and released it on the ignition cycle | Read stored codes and their freeze-frame data, which is the only record of the conditions at the moment it happened. Note what the car was doing: uphill, hot, wet, accelerating. | Diagnose the stored code. Do not road-test looking for a mechanical fault — this pattern says there is not one. |
| Flat under load and uphill, fine on light throttle, turbocharged engine | Boost not arriving — split charge pipe or intercooler, coked variable-geometry vanes, actuator or its vacuum supply | Compare requested against actual boost on live data, then pressure-test the charge system for leaks. Check the actuator moves through its full travel before condemning anything. | Repair the leak, free or renew the vane mechanism, or renew the actuator. The turbocharger itself is intact in most of these cases. |
| Diesel, gradual, with a history of interrupted regenerations | Particulate filter loaded — it throttles the exhaust and starves the turbocharger of the energy it runs on | Read soot and ash load, differential pressure across the filter, and the regeneration history. Ash load is the one that does not come back down. | Forced regeneration where soot is the problem; cleaning or replacement where it is ash. Find why regenerations were not completing, or it returns. |
| Gradual over months, noticeably worse the harder you drive | Exhaust restriction — a melted or collapsed catalyst monolith, often the legacy of an old misfire | Measure backpressure: under about 1.5 psi at idle and about 3 psi at 2,000 rpm on most engines. A high pre-catalyst reading with a much lower post-catalyst one names the converter. | Renew the restricted section, and repair whatever caused it. A new converter behind an unrepaired misfire fails the same way. |
| Poor power with fuel trims showing the engine running rich or lean | Air mass meter reading low, or an unmetered air leak — the management fuels for air it cannot see correctly | Compare the meter's live airflow against the expected figure for the engine at wide-open throttle, and smoke-test the induction. Trims tell you which direction the error runs. | Clean or renew the meter, or repair the leak. Do not clean a meter with anything but the correct solvent — the sensing element is fragile. |
| Runs out of fuel under sustained load, recovers when you lift | A delivery ceiling — blocked filter, tiring pump, or a restricted line | Gauge fuel pressure *under load* rather than at idle, which is where the ceiling shows. On a diesel, watch live rail pressure against the commanded value. | Renew the filter first where due, then the pump on the loaded measurement rather than on age. |
| Flat with rough running and sooty exhaust, diesel | EGR valve stuck open — exhaust gas displacing the air the engine needs | Command the valve closed on a scan tool and watch its position feedback, or inspect it directly. Live air mass well below expectation supports it. | Clean or renew the valve. Check the crankcase ventilation too, since the oil mist is what binds the soot. |
| No codes, nothing found, and the engine has covered high mileage | Mechanical — lost compression, or valve timing that has walked with a stretched chain | Compression or leak-down across all cylinders, and check cam timing against the marks. This is where to arrive last rather than where to start. | Repair on the finding. A low reading across every cylinder equally is wear; one low cylinder is a valve or a ring. |
-
Power returns after switching off and restarting
- Likely cause
- An imposed limit rather than a mechanical failure — the management withdrew power and released it on the ignition cycle
- How to confirm it
- Read stored codes and their freeze-frame data, which is the only record of the conditions at the moment it happened. Note what the car was doing: uphill, hot, wet, accelerating.
- What fixes it
- Diagnose the stored code. Do not road-test looking for a mechanical fault — this pattern says there is not one.
-
Flat under load and uphill, fine on light throttle, turbocharged engine
- Likely cause
- Boost not arriving — split charge pipe or intercooler, coked variable-geometry vanes, actuator or its vacuum supply
- How to confirm it
- Compare requested against actual boost on live data, then pressure-test the charge system for leaks. Check the actuator moves through its full travel before condemning anything.
- What fixes it
- Repair the leak, free or renew the vane mechanism, or renew the actuator. The turbocharger itself is intact in most of these cases.
-
Diesel, gradual, with a history of interrupted regenerations
- Likely cause
- Particulate filter loaded — it throttles the exhaust and starves the turbocharger of the energy it runs on
- How to confirm it
- Read soot and ash load, differential pressure across the filter, and the regeneration history. Ash load is the one that does not come back down.
- What fixes it
- Forced regeneration where soot is the problem; cleaning or replacement where it is ash. Find why regenerations were not completing, or it returns.
-
Gradual over months, noticeably worse the harder you drive
- Likely cause
- Exhaust restriction — a melted or collapsed catalyst monolith, often the legacy of an old misfire
- How to confirm it
- Measure backpressure: under about 1.5 psi at idle and about 3 psi at 2,000 rpm on most engines. A high pre-catalyst reading with a much lower post-catalyst one names the converter.
- What fixes it
- Renew the restricted section, and repair whatever caused it. A new converter behind an unrepaired misfire fails the same way.
-
Poor power with fuel trims showing the engine running rich or lean
- Likely cause
- Air mass meter reading low, or an unmetered air leak — the management fuels for air it cannot see correctly
- How to confirm it
- Compare the meter's live airflow against the expected figure for the engine at wide-open throttle, and smoke-test the induction. Trims tell you which direction the error runs.
- What fixes it
- Clean or renew the meter, or repair the leak. Do not clean a meter with anything but the correct solvent — the sensing element is fragile.
-
Runs out of fuel under sustained load, recovers when you lift
- Likely cause
- A delivery ceiling — blocked filter, tiring pump, or a restricted line
- How to confirm it
- Gauge fuel pressure *under load* rather than at idle, which is where the ceiling shows. On a diesel, watch live rail pressure against the commanded value.
- What fixes it
- Renew the filter first where due, then the pump on the loaded measurement rather than on age.
-
Flat with rough running and sooty exhaust, diesel
- Likely cause
- EGR valve stuck open — exhaust gas displacing the air the engine needs
- How to confirm it
- Command the valve closed on a scan tool and watch its position feedback, or inspect it directly. Live air mass well below expectation supports it.
- What fixes it
- Clean or renew the valve. Check the crankcase ventilation too, since the oil mist is what binds the soot.
-
No codes, nothing found, and the engine has covered high mileage
- Likely cause
- Mechanical — lost compression, or valve timing that has walked with a stretched chain
- How to confirm it
- Compression or leak-down across all cylinders, and check cam timing against the marks. This is where to arrive last rather than where to start.
- What fixes it
- Repair on the finding. A low reading across every cylinder equally is wear; one low cylinder is a valve or a ring.
Codes that produce this symptom (844)
Listed with the codes that most typically present this way first — the likeliest place to start.
- P0001 Fuel Volume Regulator A Control Circuit/Open Typical of this code Stop driving High
- P0002 Fuel Volume Regulator A Control Circuit Range/Performance Typical of this code Stop driving High
- P0003 Fuel Volume Regulator A Control Circuit Low Typical of this code Stop driving High
- P0004 Fuel Volume Regulator A Control Circuit High Typical of this code Stop driving High
- P0008 Engine Position System Performance — Bank 1 Typical of this code Stop driving High
- P0009 Engine Position System Performance — Bank 2 Typical of this code Stop driving High
- P0010 A Camshaft Position Actuator A Control Circuit/Open Bank 1 Typical of this code Moderate
- P0011 Camshaft Position A — Timing Over-Advanced or System Performance (Bank 1) Typical of this code Moderate
- P0012 Camshaft Position A — Timing Over-Retarded (Bank 1) Typical of this code Moderate
- P0013 B Camshaft Position Actuator A Control Circuit/Open Bank 1 Typical of this code Moderate
- P0014 B Camshaft Position — Timing Over-Advanced or System Performance Bank 1 Typical of this code Moderate
- P0016 Crankshaft Position — Camshaft Position Correlation (Bank 1 Sensor A) Typical of this code Stop driving High
- P0017 Crankshaft Position — Camshaft Position Correlation (Bank 1 Sensor B) Typical of this code Stop driving High
- P0018 Crankshaft Position — Camshaft Position Correlation (Bank 2 Sensor A) Typical of this code Stop driving High
- P0019 Crankshaft Position — Camshaft Position Correlation (Bank 2 Sensor B) Typical of this code Stop driving High
- P0020 A Camshaft Position Actuator A Control Circuit/Open Bank 2 Typical of this code Moderate
- P0021 Camshaft Position A — Timing Over-Advanced or System Performance (Bank 2) Typical of this code Moderate
- P0022 Camshaft Position A — Timing Over-Retarded (Bank 2) Typical of this code Moderate
- P0023 B Camshaft Position Actuator A Control Circuit/Open Bank 2 Typical of this code Moderate
- P0024 B Camshaft Position — Timing Over-Advanced or System Performance Bank 2 Typical of this code Moderate
- P0026 Intake Valve Control Solenoid Circuit Range/Performance — Bank 1 Typical of this code Moderate
- P0027 Exhaust Valve Control Solenoid Circuit Range/Performance — Bank 1 Typical of this code Moderate
- P0028 Intake Valve Control Solenoid Circuit Range/Performance — Bank 2 Typical of this code Moderate
- P0029 Exhaust Valve Control Solenoid Circuit Range/Performance — Bank 2 Typical of this code Moderate
- P0033 Turbocharger/Supercharger Bypass Valve A Control Circuit Typical of this code Moderate
Information, not instruction
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.
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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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