Crankshaft Position Sensor Failure
The crankshaft position sensor (CKP) reads the position and rotational speed of the crankshaft and sends this signal to the ECU. The ECU uses this data to control ignition timing and fuel injection. When the sensor fails, the ECU cannot determine crankshaft position, resulting in a no-start or intermittent stalling condition. This is one of the most common and affordable Mercedes repairs, but it mimics more serious problems like EIS failure or fuel pump failure.
Which models are at risk.
Warning signs to watch for.
Engine cranks but will not start (no-start, cranks normally)
Intermittent stalling while driving, especially when warm
Engine starts then immediately dies
Check engine light with P0335 or P0336 crankshaft position sensor codes
Rough running or misfires at certain RPM ranges
Why this happens.
Internal Hall-effect sensor element degrades from heat exposure over time
Wiring harness connector corrodes from moisture and engine bay heat
Sensor air gap changes due to debris accumulation on the reluctor ring
Heat soak causes intermittent signal loss — the sensor works when cold but fails when hot
Physical damage to the sensor or reluctor wheel from timing chain debris
How we diagnose it.
- 01
Scan for fault codes — P0335 (CKP circuit malfunction) or P0336 (CKP range/performance) confirms the sensor
- 02
Monitor the crankshaft RPM signal with Star Diagnostic during cranking — missing or erratic signal confirms failure
- 03
Check the sensor connector for corrosion, bent pins, or moisture intrusion
- 04
Measure sensor resistance with a multimeter (typically 800-1400 ohms, model-dependent)
- 05
If the issue is intermittent, test when the engine is at operating temperature — heat-related failures are common
How we fix it.
Crankshaft position sensor replacement (OEM sensor)
Simple repair; OEM sensor is reliable; resolves the no-start immediately; typically 30-60 minutes labor
Sensor location varies by engine — some engines require more disassembly for access
Sensor replacement with wiring harness repair
Addresses both the sensor and any wiring degradation; prevents future intermittent faults
Slightly more expensive; only necessary if the wiring is visibly damaged or corroded
Keep it from happening.
There is no specific preventive maintenance for the CKP sensor — it is a wear item
If your Mercedes is over 100,000 miles, consider proactive replacement during other engine work
Ensure engine bay wiring harnesses are not chafing against hot components
Keep a known-good spare sensor in the trunk for high-mileage vehicles — it is a $30-60 part
Common questions.
How do I tell the difference between a CKP sensor failure and an EIS failure?
With a CKP sensor failure, the engine will crank normally (the starter turns the engine) but will not fire and start. With an EIS failure, the key typically will not turn, or the engine will not crank at all. If the engine cranks strong but does not start, the CKP sensor is a primary suspect.
Can a bad CKP sensor cause intermittent problems?
Absolutely. Heat-related CKP sensor failures are very common in Mercedes. The engine may start and run fine when cold, then stall after 20-30 minutes of driving when the engine bay heats up. It may then restart after cooling down for 30 minutes. This intermittent behavior is the hallmark of a failing CKP sensor.
Is this an expensive repair?
No — this is one of the most affordable Mercedes repairs. The sensor itself costs $30-80 for an OEM part, and labor is typically under $200. The challenge is in diagnosis, as the symptoms can mimic more expensive problems. A proper scan with Star Diagnostic quickly identifies the issue.
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Learn more →Let’s take care of your Mercedes.
Give us a call. We’ll diagnose the problem with factory tooling and give you an honest assessment before any work begins.
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