Bad Crankshaft Position Sensor Symptoms

Match the behavior before choosing a part

If your car struggled to start and now shakes at idle, we'd put diagnosis ahead of buying a sensor because ignition and fuel-system faults can look much the same. Your observations give the investigation a starting point; inspection and testing establish what's actually wrong.

Why one signal affects so much

The crankshaft position sensor, also called the CKP sensor, tells the engine computer where the crankshaft is and how fast it's turning. That information helps the computer coordinate fuel injection and ignition timing. A missing or inaccurate signal can therefore affect both starting and the way the engine runs.

Think of the signal as timing information the computer needs to do its job. When that information becomes unreliable, fuel delivery and spark timing can suffer together, so one fault can show up as several different changes behind the wheel.

That connection explains why a sensor problem can feel like a fueling or ignition problem. Those systems depend on the crankshaft signal, while faults within the ignition or fuel-injection system can also cause similar behavior.

It struggles to start or stalls

When the computer loses the crankshaft information it needs during starting, the engine may struggle to start or fail to start altogether. Cold-engine starting trouble can appear alongside misfire or shaking at idle. Note whether the problem happened on the first start or after the engine had already been running.

Delphi's UK guidance describes a possible pattern in which an engine keeps running after a crankshaft sensor issue develops, with trouble becoming apparent at a later restart. That makes a failed restart relevant even when the previous run seemed uneventful.

Innova identifies another possible response: an internal CKP fault can interrupt the signal to the engine computer and cause hard starting or stalling. Continued running and stalling are both possible patterns, so describe the sequence your car actually showed.

The warning light can be on or absent

An engine computer receiving missing or troubling crankshaft information may turn on the check-engine light. The same light also covers many other faults, so its useful message is that the vehicle needs assessment. Diagnostic information helps narrow the investigation.

Delphi's UK guidance also notes that, depending on the vehicle's camshaft-sensor arrangement, a crankshaft sensor problem may produce neither an engine warning light nor a fault reported by the diagnostic tool. Give starting and running symptoms their own place in your notes, even when the dashboard stays quiet.

If you already have a diagnostic report, these descriptions distinguish the reported crankshaft sensor A circuit faults. Keep the exact code with your observations because an intermittent fault, a low input and a range/performance fault describe different signal problems.

• P0339 identifies an intermittent crankshaft position sensor A circuit fault.
• P0337 identifies low input from the crankshaft position sensor A circuit.
• P0338 identifies high input from the crankshaft position sensor A circuit.
• P0336 identifies a crankshaft position sensor A circuit range/performance fault.
• P0335 identifies a crankshaft position sensor A circuit malfunction.

A circuit code does not by itself confirm a failed sensor; damaged or faulty wiring can interfere with the signal, so diagnosis needs to account for that path too.

The engine shakes or misfires

Shaking while the engine idles can fit a crankshaft signal problem. Inaccurate position information can also cause misfire, leaving the engine running unevenly. These are useful details to describe separately: shaking while idling and an engine that misfires give a clearer picture than saying it simply feels wrong.

Arrange inspection and testing with a repair shop when you suspect a crankshaft sensor fault, and tell them about the starting behavior and any idle shaking. If the engine is misfiring, seek repair as soon as possible because the fault can damage components.

Confirmation means sorting out whether the crankshaft signal is responsible or whether an ignition or fuel-injection fault is producing the same behavior. That distinction determines which problem needs repair.

Acceleration weakens and fuel use rises

Mixed or missing crankshaft signals can leave acceleration weak or unresponsive because the computer relies on that information to manage fuel injection. Uneven acceleration is another possible sign. Describe a change you've already felt, including whether the engine seemed short of power or responded unevenly.

Incorrect timing information can also make combustion less effective. The engine may sputter, produce less power and consume more fuel to deliver the same performance. Using more fuel over the same distance is a useful change to note alongside the running symptoms.

An engine that continues running with a faulty crankshaft sensor may enter limp mode, with reduced performance and poorer fuel economy. This is a possible response, and higher fuel consumption also has other causes. Keep the power change and fuel-use change together in your symptom history.

What can disrupt the crankshaft signal

Loose, worn or damaged wiring can disrupt communication between the sensor and engine computer. Incorrect voltage can also interrupt that communication. This puts the electrical path among the possibilities a diagnosis needs to consider, alongside the sensor itself.

The sensor can also suffer physical damage. Excessive engine heat can melt its plastic covering, and contact with another component or road debris can damage it. These are possible explanations for a fault, rather than a reason to assign every starting problem to heat or impact.

On sensors that contain magnets, accumulated dirt can interfere with sensing rotation, and an aging magnet can become less capable of supporting an accurate signal. Damage to the components the sensor monitors can also distort the information reaching the computer. The underlying problem can therefore sit at several points in the sensing system.

Put the symptom history in order

While parked, write down the sequence you remember. A car that struggled on a cold start, one that wouldn't restart after running and one that stalled have different symptom histories worth preserving.

Add whether the check-engine light appeared and whether the engine shook at idle or misfired. If you already have a diagnostic report, copy its exact codes alongside those observations. Keep what the car did and what the report recorded as separate entries.

Finish your notes with any existing change in acceleration, power or fuel use over the same distance. You now have the observed behavior, its timing and any reported faults together for the diagnosis.