P0342
PowertrainCamshaft Position Sensor "A" Circuit Low Input
You turn the key and it cranks for ages before catching, or it fires up but idles rough and feels gutless when you pull away. That's the classic feel of P0342. The ECU watches the camshaft position sensor on bank 1 to know exactly where the cam is, so it can time the spark and injectors correctly. When that signal drops too low or keeps dropping out, the ECU loses its reference, throws this code, and often pulls the engine into a protective limp mode until it sorts itself out.
ⓘ Information only. This page provides general educational information about fault code P0342. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0342 mean?
P0342 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Camshaft Position Sensor "A" Circuit Low Input.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine light on, sometimes flickering on and off as the signal comes and goes
- • Long crank before it catches, or it just turns over and over and won't start at all
- • Rough, hunting idle that won't settle
- • Hesitation or a flat spot pulling away from a junction or a standstill
- • Limp mode kicking in: revs capped, throttle feels dead
- • Stalling at idle or as you come to a stop, then sometimes restarting fine
Possible causes
Causes commonly associated with P0342, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Faulty cam sensor on bank 1, the most common cause. These sensors get heat-soaked and oil-fouled over the years and the signal goes weak. Common on the VAG 1.6/2.0 TDI lump and plenty of older petrols
- 2. Damaged or oil-soaked wiring at the sensor plug. Cam sensors live in a hot, dirty spot and the connector pins corrode or the loom chafes against something
- 3. Poor earth or a loose pin in the sensor connector, which drops the voltage below what the ECU wants to see
- 4. Weak battery or a failing charging system. On some cars a low supply voltage drags the sensor signal under threshold, especially on cold mornings
- 5. Oil contamination on the sensor tip from a leaking cam cover gasket, which is well worth checking on engines known for weepy gaskets
- 6. A stretched timing chain throwing the cam out of position relative to the crank, more likely if you've also got P0016
- 7. ECM internal fault reading a good signal as low. Rare, and the last thing you should suspect, not the first
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read the freeze-frame data and check for partner codes. P0335, P0016 or a crank sensor code alongside P0342 changes the whole picture and points away from a simple sensor swap
- 2. Unplug the cam sensor and look hard at the connector and pins. Oil in the plug, green corrosion, or a pin that's backed out is a five-minute find that explains a lot of these
- 3. Check battery voltage and a quick charging test. Anything under about 12.4V resting or a dodgy alternator can be the real culprit, so rule it out before you spend money on parts
- 4. Back-probe the sensor with a multimeter or scope on a known-good unit. You should see clean pulses, roughly 0.5 to 5V depending on type. A flat or noisy trace means the sensor or its feed
- 5. Do a voltage-drop test from the sensor connector back to the ECM pin. More than about 0.5V drop tells you the fault is in the wiring or earth, not the sensor itself
- 6. If the sensor, wiring and supply all check out clean, only then start looking at timing chain stretch or the ECM. Don't jump to the ECM because it's nearly always something cheaper
Common questions about P0342
How do I know if it's actually the sensor or just the wiring on my car? +
Get the plug off and check it first. If there's oil sitting in the connector or the pins are corroded, you've likely found it, and a clean-up plus a new pin can fix it for nothing. If the plug is dry and tidy, back-probe the sensor signal and compare it against the wiring side. A weak or missing signal at the sensor but a healthy feed to it points to the sensor. A good signal at the sensor that's gone by the time it reaches the ECM means you've got a broken or corroded wire somewhere in the loom. And if you've got P0016 sat next to this code, stop poking sensors and get the cam-to-crank timing checked, because a stretched chain reads like a cam sensor fault but isn't one.
Can I just replace the sensor myself and save the labour? +
On most engines, yes. The cam sensor is usually held by one bolt and a single plug, and the part runs roughly £15 to £60 for an aftermarket one or more for OEM. The catch is access. On some transverse engines it's buried behind the cam cover or up against the bulkhead and you'll be working blind. Use a quality sensor, not the cheapest no-name off eBay, because a poor one can set the same code straight back. Clean the connector and check the cam cover gasket isn't weeping oil onto it while you're in there, or you'll be doing the job twice.
If I clear the code does it stay gone or come straight back? +
Depends entirely on whether you fixed the cause. Clear it after replacing a dead sensor or sorting a corroded plug and it stays off. Clear it with a failing sensor still fitted and it'll be back within a few drive cycles, often the next cold start. An intermittent wiring fault is the frustrating one, it'll clear and then return days or weeks later when the loom flexes the wrong way or the connector heats up. If you keep clearing it and it keeps coming back at random, that's your sign it's a connection problem, not a one-off glitch.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →