OBD2 codes.
A code identifies a signal or system that needs to be checked, not a part you should replace.
Got an OBD2 Bluetooth adapter? Read the codes straight from your car.49 code entries · 0 related faults
P0016The intake camshaft is out of sync with the crankshaft (bank 1)Urgency high
Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
The crankshaft (turned by the pistons) and the camshafts (which open the valves) turn linked by the timing chain or belt. This code means the sensor A camshaft —usually the intake one— on bank 1 (the cylinder 1 side) is not in the position that matches the crankshaft.
What the car has detected
The engine computer compares the crankshaft and camshaft sensor signals and has seen the cam running advanced or retarded by more degrees than allowed.
The most serious cause is a stretched timing chain or one that has jumped a tooth: if it gets worse, the valves can hit the pistons and wreck the engine. Avoid long trips and get it to a garage as soon as possible.
Symptoms
- Engine warning light on
- Chain noise or rattle, especially on cold start
- Rough idle or hesitation
- Loss of power or limp mode
- Hard starting
Possible causes
- Stretched timing chain (common at high mileage) or one that has jumped a tooth
- Worn timing tensioner or guides
- Stuck camshaft phaser (variable timing) or its control valve
- Low, old or wrong-viscosity oil that doesn't feed the phaser properly
- Faulty camshaft or crankshaft sensor, or a shifted reluctor wheel
- Timing assembled incorrectly after a repair
Checks for the garage
- Ask whether engine or timing work was done recently
- Check the oil level and condition
- Compare requested and actual cam angle in live data
- Look for other timing codes: several at once point to the main chain
- Verify the timing marks per the manual and the condition of chain and tensioners
- Check the phasers and their control valves
Next step
Check the oil level and have the timing (chain or belt, tensioners) and the camshaft phaser checked.
Go to a garage as soon as possible, especially if you can hear the chain. Checking timing and the chain needs specific tools and the engine manual.
Original sources · Date indicated: 2026-10-12
P0017The exhaust camshaft is out of sync with the crankshaft (bank 1)Urgency high
Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
The crankshaft (turned by the pistons) and the camshafts (which open the valves) turn linked by the timing chain or belt. This code means the sensor B camshaft —usually the exhaust one— on bank 1 (the cylinder 1 side) is not in the position that matches the crankshaft.
What the car has detected
The engine computer compares the crankshaft and camshaft sensor signals and has seen the cam running advanced or retarded by more degrees than allowed.
The most serious cause is a stretched timing chain or one that has jumped a tooth: if it gets worse, the valves can hit the pistons and wreck the engine. Avoid long trips and get it to a garage as soon as possible.
Symptoms
- Engine warning light on
- Chain noise or rattle, especially on cold start
- Rough idle or hesitation
- Loss of power or limp mode
- Hard starting
Possible causes
- Stretched timing chain (common at high mileage) or one that has jumped a tooth
- Worn timing tensioner or guides
- Stuck camshaft phaser (variable timing) or its control valve
- Low, old or wrong-viscosity oil that doesn't feed the phaser properly
- Faulty camshaft or crankshaft sensor, or a shifted reluctor wheel
- Timing assembled incorrectly after a repair
Checks for the garage
- Ask whether engine or timing work was done recently
- Check the oil level and condition
- Compare requested and actual cam angle in live data
- Look for other timing codes: several at once point to the main chain
- Verify the timing marks per the manual and the condition of chain and tensioners
- Check the phasers and their control valves
Next step
Check the oil level and have the timing (chain or belt, tensioners) and the camshaft phaser checked.
Go to a garage as soon as possible, especially if you can hear the chain. Checking timing and the chain needs specific tools and the engine manual.
Original sources · Date indicated: 2026-10-12
P0019The exhaust camshaft is out of sync with the crankshaft (bank 2)Urgency high
Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor B)
The crankshaft (turned by the pistons) and the camshafts (which open the valves) turn linked by the timing chain or belt. This code means the sensor B camshaft —usually the exhaust one— on bank 2 (the side opposite cylinder 1, only on V engines) is not in the position that matches the crankshaft.
What the car has detected
The engine computer compares the crankshaft and camshaft sensor signals and has seen the cam running advanced or retarded by more degrees than allowed.
The most serious cause is a stretched timing chain or one that has jumped a tooth: if it gets worse, the valves can hit the pistons and wreck the engine. Avoid long trips and get it to a garage as soon as possible.
Symptoms
- Engine warning light on
- Chain noise or rattle, especially on cold start
- Rough idle or hesitation
- Loss of power or limp mode
- Hard starting
Possible causes
- Stretched timing chain (common at high mileage) or one that has jumped a tooth
- Worn timing tensioner or guides
- Stuck camshaft phaser (variable timing) or its control valve
- Low, old or wrong-viscosity oil that doesn't feed the phaser properly
- Faulty camshaft or crankshaft sensor, or a shifted reluctor wheel
- Timing assembled incorrectly after a repair
Checks for the garage
- Ask whether engine or timing work was done recently
- Check the oil level and condition
- Compare requested and actual cam angle in live data
- Look for other timing codes: several at once point to the main chain
- Verify the timing marks per the manual and the condition of chain and tensioners
- Check the phasers and their control valves
Next step
Check the oil level and have the timing (chain or belt, tensioners) and the camshaft phaser checked.
Go to a garage as soon as possible, especially if you can hear the chain. Checking timing and the chain needs specific tools and the engine manual.
Original sources · Date indicated: 2026-10-12
P0087Fuel rail pressure too lowUrgency high
Fuel Rail/System Pressure - Too Low
On direct injection engines (common rail diesels and many petrol engines), fuel reaches the injectors at very high pressure from a shared pipe, the rail. A sensor measures that pressure and a regulator adjusts it. This code means rail pressure has dropped below the minimum.
What the car has detected
The engine computer has measured a rail fuel pressure below the minimum threshold for the engine's conditions.
With low pressure the engine may lose power, be slow to start or cut out while driving, which is dangerous on the road. Have it checked as soon as possible and avoid long trips.
Symptoms
- Engine warning light on
- Loss of power or limp mode
- Hard or long starting
- Hesitation or the engine cuts out while driving
Possible causes
- Clogged fuel filter or bent or squashed lines
- Weak low-pressure pump in the tank, or its strainer dirty
- Leaks on the high-pressure side or leaking injectors
- Rail pressure regulator sticking open or a worn high-pressure pump
- High-pressure pump out of time or wear of its cam and follower
- In cold weather, ice from water in the fuel at the tank pick-up strainer
Checks for the garage
- Read the other codes (for example pump timing ones) and the freeze frame data
- Compare actual and requested rail pressure in live data, at idle and when accelerating
- Command the pressure up and down with diagnostics and see whether the sensor follows
- Check power, earth and wiring of the regulator and the pressure sensor
- Measure the in-tank pump pressure with a gauge and check filter, lines and leaks
Next step
Make sure there is enough fuel and have the fuel filter, pump and possible leaks checked.
Go to a garage as soon as possible, especially if the engine pulls badly or has ever cut out. Pressure tests need diagnostics and a gauge.
Original sources · Date indicated: 2026-10-12
P0088Fuel rail pressure too highUrgency medium
Fuel Rail/System Pressure - Too High
On direct injection engines (common rail diesels and many petrol engines), fuel reaches the injectors at very high pressure from a shared pipe, the rail. A sensor measures that pressure and a regulator adjusts it. This code means rail pressure has gone above the maximum allowed.
What the car has detected
The engine computer has measured a rail fuel pressure above the maximum allowed deviation over the requested value.
You can drive carefully, but have it checked soon: if the pressure really is high, the engine may knock and smoke. Often the cause is the sensor or its wiring.
Symptoms
- Engine warning light on
- Engine sounds harsher (combustion knock)
- Smoke from the exhaust
- Loss of power or limp mode
Possible causes
- Faulty rail pressure sensor or a wiring or connector fault
- Sticking pressure regulator or valve
- Voltage drops from the battery or the engine computer's supply
- On some engines, a stretched timing chain that throws the pump out of time
Checks for the garage
- Read the other codes (for example pump timing ones) and the freeze frame data
- Compare actual and requested rail pressure in live data, at idle and when accelerating
- Command the pressure up and down with diagnostics and see whether the sensor follows
- Check power, earth and wiring of the regulator and the pressure sensor
- Check battery and charging voltage
Next step
Have the rail pressure sensor, its wiring and the pressure regulator checked.
Go to a garage if the code comes back or if you notice knocking or smoke. Checking the sensor and regulator needs diagnostics.
Original sources · Date indicated: 2026-10-12
P0089The fuel pressure regulator can't reach the requested pressureUrgency medium
Fuel Pressure Regulator 1 Performance
On direct injection engines (common rail diesels and many petrol engines), fuel reaches the injectors at very high pressure from a shared pipe, the rail. A sensor measures that pressure and a regulator adjusts it. This code means the regulator cannot achieve the pressure the engine computer requests.
What the car has detected
The engine computer compares the pressure it commands with the one it measures and has seen a difference, or a correction, larger than allowed.
You can drive carefully, but the engine may run unevenly or lose power. Get it checked soon.
Symptoms
- Engine warning light on
- Uneven running or hesitation
- Loss of power
- Hard starting
Possible causes
- Rail pressure sensor reading off or failing intermittently
- Pressure regulator or its circuit with excessive resistance
- Leaking or restricted injector
- Short circuits in nearby circuits (crankshaft sensor or camshaft actuator)
Checks for the garage
- Read the other codes (for example pump timing ones) and the freeze frame data
- Compare actual and requested rail pressure in live data, at idle and when accelerating
- Command the pressure up and down with diagnostics and see whether the sensor follows
- Check power, earth and wiring of the regulator and the pressure sensor
- Test the injectors if the circuit and sensor are fine
Next step
Have the rail pressure sensor, the regulator and its circuit, and the injectors checked.
Go to a garage if the code comes back or if the engine runs unevenly. Diagnosing the regulator and sensor needs equipment.
Original sources · Date indicated: 2026-10-12
P0101The mass air flow sensor gives readings that don't add upUrgency medium
Mass or Volume Air Flow Circuit Range/Performance
The mass air flow (MAF) sensor measures the air going into the engine; the engine computer uses it to work out how much fuel to inject. This code means the value it sends doesn't match what the engine computer expects for the current engine speed and load.
What the car has detected
The MAF signal is outside the believable range for the engine's state (it is not a cut signal, but a value that doesn't fit the rest of the data).
You can drive, but the engine may lack power or run with the wrong mixture, and in the long run use more fuel or foul the catalytic converter. Get it checked soon.
Symptoms
- Engine warning light on
- Lack of power
- Higher fuel consumption
- Rough idle, hesitation or stalling
- Hard starting
- Black smoke from the exhaust
Possible causes
- Dirty or worn MAF sensor (on some diesels it gets dirty over the years and loses accuracy)
- Air leak between the MAF sensor and the engine (air that isn't measured)
- Restricted airflow: dirty air filter, blocked screen or clogged exhaust
- Corroded or faulty MAF wiring, connector or earth points
- Mechanical loss of engine performance that makes the reading not add up
Checks for the garage
- Check the MAF wiring, connector and earth points
- Check the air filter and intake for restrictions
- Look for leaks between the MAF sensor and the engine (on turbo engines, also before the turbo)
- Compare the MAF reading in live data with the expected values at idle and when revving
- Clean the MAF sensor with a dedicated cleaner without touching the element and replace it if it doesn't improve
Next step
Check the air filter and that there are no loose hoses between the MAF sensor and the engine; if it continues, have the sensor and its connector checked.
Go to a garage if the filter and intake are fine and the code comes back, or if the car loses a lot of power. Checking the MAF signal needs diagnostic equipment.
Original sources · Date indicated: 2026-10-12
P0102Mass air flow sensor signal too lowUrgency medium
Mass or Volume Air Flow Circuit Low Input
The mass air flow (MAF) sensor measures the air going into the engine; the engine computer uses it to work out how much fuel to inject. This code means the electrical signal arriving is lower than possible, as if the sensor wasn't measuring or the circuit was broken.
What the car has detected
The voltage or frequency of the MAF signal is below the minimum a working sensor can produce.
You can drive carefully: without that reading the engine computer uses back-up values and the engine may lose power. Get it checked soon.
Symptoms
- Engine warning light on
- Loss of power or limp mode
- Hesitation or stalling
- Hard starting
- Higher fuel consumption
Possible causes
- Loose, corroded or damaged connector pins
- Broken or damaged wire between the MAF sensor and the engine computer
- Missing power supply or earth to the sensor
- Failed MAF sensor
Checks for the garage
- Check the MAF connector and wiring
- Measure the supply with the ignition on (roughly battery voltage) and the earth
- Measure the signal at idle and when revving with a multimeter or the diagnostic tool
- Replace the MAF sensor only if wiring, supply and earth are fine
Next step
Check that the MAF connector is properly fitted and free of corrosion, and have the wiring and sensor checked.
Go to a garage if the connector is fine and the code persists, or if the car goes into limp mode. Electrical measurements need a multimeter and diagnostics.
Original sources · Date indicated: 2026-10-12
P0128The engine doesn't reach its normal temperature (thermostat)Urgency low
Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
The thermostat is a valve that keeps the coolant hot until the engine reaches its working temperature. This code means the engine takes too long to warm up or doesn't reach that temperature.
What the car has detected
After several minutes of running, the coolant temperature is still below the level the thermostat should hold. It is usually stored when this happens on two trips in a row.
It is not dangerous in the short term, but the engine uses more fuel, the heater is weaker and some emissions checks don't complete. If the coolant level is also dropping, have it checked now.
Symptoms
- Engine warning light on
- The temperature gauge barely rises or takes a long time
- The heater blows only lukewarm air
- Higher fuel consumption
Possible causes
- Thermostat stuck open (the most common cause)
- Low coolant level
- Coolant temperature sensor reading too low
- Faulty intake air temperature sensor (the engine computer uses it in its calculations)
- Radiator fan that never switches off
- Water pump or heater valve not working properly
Checks for the garage
- Check the coolant level and look for leaks first
- Compare coolant, intake air and ambient temperatures with the engine cold: they should be similar
- Confirm the radiator fan switches off when it should
- Measure the coolant temperature sensor's resistance at different temperatures
- Test the thermostat and check the temperature at which it opens
- Clear the code and do two trips to confirm the repair
Next step
Check the coolant level with the engine cold and have the thermostat and engine temperature sensor checked.
Go to a garage if the coolant level is fine and the code comes back: replacing the thermostat usually means draining the system. If you are losing coolant or the gauge climbs too high, go as soon as possible.
Original sources · Date indicated: 2026-10-12
P0135Fault in the oxygen sensor heater (front sensor, before the catalytic converter)Urgency low
O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
The oxygen sensor measures oxygen in the exhaust gas and has to be very hot to work, so it has a heating element. This code means a fault in that heater circuit on the front sensor, before the catalytic converter (bank 1, sensor 1).
What the car has detected
The engine computer monitors the current drawn by the sensor heater and has seen a value too high or too low, or an open circuit.
The car usually drives the same. It may use a little more fuel and take longer to set the mixture correctly when cold, and it may fail the emissions inspection. It can wait, but it should be repaired.
Symptoms
- Engine warning light on
- Slightly higher fuel consumption
- Slower mixture control with a cold engine
- Usually no change when driving
Possible causes
- Failed sensor heating element (the most common cause)
- Blown heater fuse
- Damaged wiring or a corroded or melted connector near the exhaust
- Open control circuit or, less often, a fault in the engine computer
Checks for the garage
- Check the heater fuse; if it blows again, suspect the sensor
- Inspect the connector and wiring for corrosion, melted pins or contact with the exhaust
- Measure the heater resistance and compare it with the specification
- Check that power arrives with the ignition on and that the engine computer switches the control on
- Replace the sensor if the fuse and wiring are fine and the resistance is wrong
Next step
Have the sensor heater fuse, its wiring and the sensor's resistance checked before replacing the sensor.
If the fuse is fine, the garage needs to measure the circuit and the sensor. It is not urgent, but repair it before the next inspection.