Symptoms of a Bad Crankshaft Position Sensor on a BMW

A failing crankshaft position sensor on a BMW typically causes hard or no starting, sudden stalling, misfires, loss of power, erratic tachometer readings, and the Check Engine Light—often with trouble codes like P0335. Understanding these symptoms in more detail can help BMW owners distinguish a sensor issue from other engine or fuel-related problems and decide when to seek professional diagnosis.

Why the Crankshaft Position Sensor Matters on a BMW

The crankshaft position sensor (often called the “crank sensor”) tells the engine control unit (ECU/DME in BMW terminology) where the crankshaft is in its rotation and how fast it’s spinning. This data is critical for precise fuel injection timing and ignition timing. When the sensor fails or sends erratic signals, the DME can’t reliably fire the injectors or spark plugs, leading to a range of drivability issues that can escalate from mild hesitation to complete engine shutdown.

Most Common Symptoms of a Bad Crankshaft Position Sensor

1. Engine Cranks but Won’t Start

One of the hallmark symptoms on many BMW models is an engine that turns over strongly but simply refuses to start. The starter motor works, the battery is fine, and you may even smell fuel, but the engine never actually fires.

In this scenario, the DME may not be seeing a valid crank signal, so it does not know when to trigger spark or fuel injection. As a result, the car can behave as if it is out of time or totally disabled, even though mechanical components are intact. Intermittent failures can mean the car starts sometimes and not others, particularly when hot.

2. Intermittent Stalling While Driving

A failing BMW crank sensor can cause the engine to shut off suddenly while driving, often without warning. The engine may die as if you turned the key off, sometimes restarting immediately, sometimes only after it cools down.

This is frequently described by owners as random, unpredictable stalling: the car runs fine for miles, then abruptly loses all power. Heat-related failure is common—sensors may work when cold, then fail once engine temperature rises, returning when cooled. This pattern can be a strong clue pointing to a crank sensor instead of a fuel pump or ignition coil issue.

3. Hard Starting and Extended Cranking

Instead of a total no-start, some BMWs with a weak crank sensor take noticeably longer to start. The engine may crank for several seconds before catching, especially after the car has been driven, shut off, and restarted while warm.

In these cases, the sensor is still providing some signal but not cleanly or reliably. The DME struggles to sync ignition and injection timing, causing delayed starts, rough initial idle, or a brief stumble right after the engine fires. Drivers may notice the issue gradually getting worse over weeks or months.

4. Misfires, Rough Idle, and Hesitation

A degrading crank sensor can also show up as rough running rather than outright stalling. The engine may misfire under load, idle roughly at stoplights, or hesitate during acceleration.

When the crankshaft signal is noisy or inconsistent, the timing for spark and fuel can vary, leading to cylinders firing late, weakly, or not at all on some cycles. While ignition coils, spark plugs, and injectors are also common misfire culprits on BMWs, a crank sensor problem is more likely if misfires coincide with other symptoms like hot-start issues or random stalling.

5. Loss of Power and Poor Acceleration

Drivers may feel a general drop in performance when the crank sensor is on its way out. Acceleration can feel flat, throttle response sluggish, and the car may struggle to rev freely, especially at higher RPMs.

The DME may enter a fallback or “limp” style strategy to protect the engine when it detects crank signal irregularities, reducing power or limiting revs. This protective behavior can mimic other issues like a failing MAF sensor or clogged catalytic converter, but diagnostic trouble codes and symptom patterns help narrow it down.

6. Erratic or Dead Tachometer Reading

On some BMW models, the tachometer (RPM gauge) reads directly or indirectly from the crankshaft sensor data. When the sensor signal drops out, the tach can behave strangely: bouncing, freezing, or dropping to zero even while the engine is still trying to run.

Although not every model’s tach is affected the same way, an RPM gauge that cuts out or lags at the exact moment the engine misbehaves is a useful visual clue that the crank signal may be compromised rather than a purely fuel-related issue.

7. Check Engine Light and Related Fault Codes

A bad crankshaft position sensor will frequently trigger the Check Engine Light (CEL) on BMWs, though in some intermittent cases it may not illuminate immediately. When scanned with an OBD-II scanner or BMW-specific diagnostic tool (like ISTA or INPA), the following codes are commonly found:

This list highlights the most frequent diagnostic trouble codes that point toward a crankshaft sensor or crankshaft signal issue on BMWs.

• P0335 – Crankshaft Position Sensor “A” Circuit (generic OBD-II)
• P0336–P0339 – Various crankshaft sensor range, performance, and circuit issues
• BMW-specific faults for “Crankshaft sensor: signal” or “Crankshaft: synchronization” (exact wording varies by DME and model)
• Sometimes related codes for camshaft position sensors if the DME detects mismatch between cam and crank signals

While fault codes do not guarantee the sensor itself is defective (wiring issues and connector corrosion can create similar errors), seeing these specific crankshaft-related codes alongside the drivability symptoms strongly directs attention toward that sensor and its circuit.

How Symptoms Differ Across BMW Models and Engines

Common Patterns Across Generations

Despite variations in design between older inline-six engines (such as the M52/M54), newer turbocharged four- and six-cylinder engines (N20, B48, N55, B58), and V8 units, crank sensor failure symptoms are broadly similar:

The following list outlines how crankshaft position sensor issues tend to present themselves across most BMW platforms.

• Older models (E36, early E46, E39, etc.): Often show intermittent hot-start issues and sudden stalling; sensors may fail gradually with heat cycling.
• Mid-2000s to early 2010s models (E90, E60, E70, etc.): Check Engine Light and limp-mode incidents more common, as DMEs use more advanced fault strategies.
• Newer F- and G-series models: More precise monitoring can log crank signal irregularities early, sometimes before severe drivability problems appear.

Although the electronic sophistication of BMW engines has evolved, the fundamental signs of crank sensor failure have stayed remarkably consistent—primarily in how they disrupt starting, stalling, and smooth engine operation.

Heat-Related and Intermittent Failures

Many BMW owners report that crank sensor issues are strongly temperature dependent. The car may run perfectly when cold, then act up once fully warmed, especially after a brief stop.

This symptom pattern is particularly important because it can mislead owners into suspecting the battery or starter when the real issue is a heat-soaked sensor whose internal electronics break down at higher temperatures and recover when cooled.

How to Distinguish a Bad Crank Sensor from Similar Problems

Symptoms That Overlap with Other Faults

Several other common BMW problems can imitate some of the crank sensor symptoms, so accurate diagnosis is critical before replacing parts:

The next list summarizes issues that can appear similar to a crankshaft sensor fault and notes how they typically differ in behavior.

• Failing fuel pump or clogged fuel filter: Often cause poor acceleration, surging, or stalling under heavy load, but the engine may still start reliably until the pump fails completely.
• Ignition coil or spark plug issues: Usually present as cylinder-specific misfires, roughness at certain RPMs or loads, and corresponding misfire codes (e.g., P0301–P0306) rather than crank sensor codes.
• Camshaft position sensor issues: Can also cause hard starts and misfires, but often allow the car to run in a limp mode, with codes pointing to cam sensors instead of crank.
• Battery, alternator, or main power issues: Typically bring dim lights, slow cranking, or electrical glitches, not clean sudden engine shutdown at speed with a strong crank afterward.
• Immobilizer or key problems: May cause a no-start, but the DME usually won’t activate the starter or fuel system, and the symptom pattern differs once security faults are scanned.

Because these conditions can mimic or overlap with crank sensor failure, using scan tools, checking live data, and inspecting wiring is usually necessary to pinpoint the true cause rather than relying on symptoms alone.

Diagnostic Clues Specific to the Crank Sensor

Technicians and experienced DIYers will look for a few specific clues when they suspect the crankshaft position sensor on a BMW:

The following list outlines practical diagnostic steps that help confirm whether the crank sensor is the primary culprit.

• No RPM signal during cranking: On diagnostic tools, if RPM stays at 0 while the engine is cranking, the crank sensor signal may be missing.
• Watching crankshaft speed or sync status while the engine runs can reveal momentary signal losses right before stalling.
• Heat test: Problems that appear only when hot and disappear when cool are classic for aging sensors.
• Connector and wiring inspection: Corrosion, oil contamination, or damaged wiring near the sensor can cause intermittent or weak signals.
• Resistance or waveform testing: On some engines, measuring sensor resistance or viewing the waveform with an oscilloscope can confirm failure.

These diagnostic approaches help differentiate between a genuine sensor failure, a wiring or connector fault, and unrelated engine or fuel system problems, allowing for more precise and cost-effective repairs.

Safety and Next Steps if You Suspect a Bad Crank Sensor

Driving Risks

Because a bad crankshaft position sensor can cause sudden, complete engine shutdown, it presents a safety risk—especially at highway speeds, in heavy traffic, or during turning maneuvers. Loss of engine power can reduce power steering assistance and brake boost, making the car harder to control.

For this reason, BMW owners who experience repeated stalling or no-start conditions linked to crank sensor faults should avoid extended driving until the issue is diagnosed and repaired. Continuing to drive the vehicle may leave you stranded or force emergency maneuvers if the engine cuts out in motion.

When to Seek Professional Diagnosis

If your BMW shows several of the symptoms described—particularly a combination of intermittent stalling, hot-start problems, and crankshaft-related fault codes—professional diagnosis is strongly recommended. Modern BMWs use complex electronics, and guessing at parts can quickly become expensive.

A reputable BMW specialist or dealer with factory-level diagnostic tools can quickly confirm whether the crank sensor is at fault, whether the wiring is damaged, or whether another system is causing similar behavior. Early attention can prevent tow bills, safety risks, and unnecessary replacement of unrelated components.

Summary

A bad crankshaft position sensor on a BMW typically reveals itself through a cluster of symptoms: hard or no starting despite good cranking, sudden or intermittent stalling (often when hot), rough idle and misfires, reduced power, erratic or dead tachometer readings on some models, and a Check Engine Light with crankshaft-related fault codes such as P0335. These problems stem from the DME losing accurate information on crankshaft position and speed, disrupting ignition and fuel timing.

While other issues—like fuel pump failure, ignition problems, or camshaft sensor faults—can mimic some of these signs, the pattern of heat-related intermittent failure, no-RPM readings during cranking, and specific diagnostic codes strongly points toward the crank sensor or its wiring. Because a failing crank sensor can cause sudden engine shutdown and safety risks, prompt diagnosis and repair by a qualified technician is the most reliable way to restore normal, safe operation of your BMW.