Timing and crank/cam sensorsGeneric OBD-II codeUrgency: As soon as possible

P0340 on Mercedes-Benz: causes and affected engines

P0340 means: camshaft position sensor "A" circuit (bank 1 or single sensor).^[1][2][3] Mercedes-Benz has 6 documented faults that can trigger it, across 6 engines, including OM651, M271, OM654 and OM642. Only a diagnosis can confirm the cause on your car.

Documented faults

that can trigger it

Engines

used by Mercedes-Benz, with at least one of them

Mercedes-Benz models

with at least one of these faults

Urgency

As soon as possible

Reviewed on 2 October 20264 sources How we work

Documented faults in Mercedes-Benz engines that can trigger P0340

Grouped by engine or model, from most to least important. These are faults with the timing chain and with the timing belt: not all of them will necessarily set the code, and only a diagnosis confirms the cause on your car.

OM651

In CLA C117, Clase A W176, Clase B W246, Clase C W204, Clase C W205, Clase E W212 and 9 more models

- Critical severityFrequency: Very frequentTimingTiming chain stretch and tensioner failureYes: the OM651 timing chain can stretch prematurely, above all on units built up to 2013, and in 2014-2015 Mercedes-Benz recalled around 114,000 vehicles in Germany over a defective sealing ring in the tensioner. A metallic rattle on a cold start is the first sign.Repair (garage): €2,000–€3,500Appears at around 120,000 km

M271

In Clase C W203, Clase C W204, Clase E W211, Clase E W212, CLK C209, SLK R171 and SLK R172

- Critical severityFrequency: CommonTimingTiming chain stretch and wear of the camshaft sprocketsYes: the M271 timing chain can stretch prematurely and wear the teeth of the camshaft sprockets, with a risk of damaging the engine. A specialist source describes this weak point as persistent throughout production, including the EVO turbo revision.

OM654

In Clase C W205, Clase E W213, Clase V W447, CLS C257, GLC X253 and Vito W447

- Critical severityFrequency: CommonTimingTiming chain wear or breakage (2016 to 2021 units)Yes: Mercedes-Benz recalled OM654 units built between January 2016 and February 2021 because the timing chain can wear and even break, risking engine damage. The campaign has already been carried out at official workshops; you should check whether the vehicle received it.

OM642

In Clase E W211, Clase G W463, Clase M W164, Clase R W251, CLS C219, GL X164 and 2 more models

- Critical severityFrequency: OccasionalTimingRear timing chain wear and tensioner failureThe OM642's timing chain, at the rear next to the gearbox, usually lasts a long time: normal stretch begins at around 300,000-350,000 km. On older units (up to 2009) cases of premature tensioner failure have been documented, uncommon but serious if the chain skips.Repair (garage): €3,500–€5,000Appears at around 300,000 km

1.2 TCe

In Citan W415

- High severityFrequency: OccasionalTimingTiming chain stretch and breakageThe 1.2 TCe chain has no scheduled replacement, but in engines that burn oil the low level makes the camshaft phaser vibrate and the chain stretches until it becomes noisy or breaks. The dealer network replaces the tensioner if compression is good; if not, the short block or the engine.

M270/M274

In CLA C117, Clase A W176, Clase B W246, Clase C W205, Clase E W212, Clase E W213 and 3 more models

- Medium severityFrequency: RareTimingTiming chain and tensioner: a strong point compared with earlier enginesGenerally no: unlike earlier Mercedes engines, the M270/M274 timing chain is not a common source of faults. The specialist workshops consulted agree that it hardly gives any trouble now, with only isolated cases cited online.

Common causes of P0340 on any make

From most to least likely, according to the sources.

1Faulty or failing camshaft sensor. Carista considers it the most common cause: over time, the internal Hall element degrades from heat.^[1][2][4]
2Damaged wiring or connector: grounded, short-circuited or worn wires, or a corroded or oil-soaked connector. Carista points out that this is common at the connector next to the timing cover on high-mileage engines.^[1][2][3][4]
3Dirty or damaged camshaft reluctor ring (tone wheel), producing missing pulses.^[2][4]
4Worn timing chain or belt (a stretched chain, or one that has jumped a tooth).^[2][4]

What to check first

The first diagnostic steps, from the most likely and cheapest to check to the most expensive.

1Read all the codes with a diagnostic tool and see whether there are others (P0335, P0341, P0016, misfires). Then clear the code and check whether it comes back.^[4]
2Inspect the sensor connector and its wiring: oil, corrosion, broken, chafed or grounded wires.^[1][2][3][4]
3With the diagnostic tool, compare the camshaft position with the crankshaft position in live data: they should stay in phase.^[2]

Full guide to P0340: symptoms, diagnosis and whether you can drive

Parts related to code P0340 on Mercedes-Benz cars

The parts that most often cause this code. The code points to the circuit, not always the part: diagnose before you buy.

Timing chain kit
- Buy part at Autodoc (affiliate link, opens in a new tab)
Timing kit
- Buy part at Autodoc (affiliate link, opens in a new tab)
Alternator
- Buy part at Autodoc (affiliate link, opens in a new tab)

Affiliate links: if you buy from these shops, MotorFiable may receive a commission at no cost to you. Check compatibility against the registration plate or VIN before ordering. Affiliate links

Frequently asked questions

Which Mercedes-Benz engines have faults that can trigger P0340?

OM651 (1 fault), M271 (1 fault), OM654 (1 fault), OM642 (1 fault), 1.2 TCe (1 fault) and M270/M274 (1 fault). Each fault has its own page with the affected years and versions, the symptoms and the repair cost.

What does code P0340 mean on a Mercedes-Benz?

Camshaft position sensor "A" circuit (bank 1 or single sensor). The ECU has detected a fault in the camshaft position sensor "A" circuit (bank 1 or single sensor): it is not receiving a valid signal telling it where the camshaft is. It uses that data to coordinate ignition timing and fuel injection. It is a generic OBD-II code: it means the same on a Mercedes-Benz as on any other make.^[1][2][3][4]

Can I keep driving with P0340?

As soon as possible. The sources agree that this is not a fault to ignore. Autodoc Club considers it a safety hazard, because the car may not start or may start with great difficulty, and urges fixing it immediately to avoid serious engine damage; MechanicBase rates it as serious and advises against driving with it, mainly because of the risk of losing power in the middle of traffic; and Carista gives it a high severity and cites sudden stalling while driving, followed by long cranking before the engine restarts.^[1][2][4]

Sources

Every fact on this page links to its source. If you find an error, let us know.

Código OBD2 P0340: causas, síntomas y cómo corregirloAutodoc Club · Technical documentation · consulted 2 October 2026 · in Spanish
P0340: OBD-II code P0340 flags a fault in the camshaft position sensor circuitCarista · Technical documentation · consulted 2 October 2026
DTC P0340 Camshaft position sensor "A" circuit (bank 1 or single sensor), Saab 9-2X (9346) 2005, 2.5iSaab WIS Online (Saab Workshop Information System) · Technical documentation · consulted 2 October 2026
What Does The P0340 Code Mean?Mechanic Base · Technical documentation · consulted 2 October 2026