P0335 Mers: Crankshaft Position Sensor A Circuit Malfunction – Complete Diagnostic Guide
Quick Summary: The P0335 code in Mers vehicles indicates a malfunction in the crankshaft position sensor circuit. This critical sensor provides essential data to your engine’s computer for proper ignition timing and fuel injection. When faulty, it can cause no-start conditions, stalling, and poor engine performance. This comprehensive guide provides detailed diagnostic procedures, cost estimates, and repair solutions.
1.0 Understanding the P0335 Code in Mers Vehicles
The P0335 – Crankshaft Position Sensor “A” Circuit Malfunction is a generic powertrain code that indicates your Mers’ Engine Control Module (ECM) is not receiving a valid signal from the crankshaft position sensor (CKP Sensor). This sensor is fundamental to modern engine management systems, acting as the primary source of information about engine position and speed.
The crankshaft position sensor monitors the rotational speed and precise position of the crankshaft. This data enables the ECM to calculate optimal timing for:
- Ignition spark delivery to each cylinder at the exact moment for efficient combustion
- Fuel injector pulse timing to ensure the correct air-fuel mixture
- Variable valve timing system operation (if equipped) for optimal engine performance
- Engine misfire detection by monitoring crankshaft acceleration patterns
- Cylinder deactivation systems (in some models) for improved fuel economy
- Transmission shift points calculation based on engine load and speed
When the ECM detects an implausible signal, no signal, or signal interruptions from this sensor for a predetermined period (typically two consecutive drive cycles), it will trigger the P0335 code, illuminate the check engine light, and may default to a pre-programmed limp mode with reduced performance to prevent engine damage.
Technical Note: The crankshaft position sensor typically works in conjunction with the camshaft position sensor. While the ECM can sometimes infer engine position from the camshaft sensor alone, the crankshaft sensor provides the primary timing reference needed for precise ignition and fuel delivery.
2.0 Symptoms of P0335 in Mers Vehicles
When the P0335 code is stored in your Mers’ ECM, you may experience one or more of the following symptoms, ranging from mild drivability issues to complete engine failure:
- Engine Cranks But Won’t Start: The most definitive symptom. Without crankshaft position data, the ECM cannot synchronize fuel injection and ignition timing, preventing combustion. This occurs because the ECM doesn’t know when to fire the injectors and ignition coils.
- Intermittent Stalling: The engine may start but stall unexpectedly during idle, deceleration, or under load when the sensor signal drops out momentarily. This is particularly common with wiring issues or failing sensors that work when cold but fail when hot.
- Extended Cranking Time: The engine may require significantly longer cranking before starting as the ECM struggles to establish synchronization with an intermittent or weak sensor signal.
- Rough Idle and Misfires: Inconsistent sensor signals can cause improper spark timing, leading to rough running and potential misfire codes (P0300-P0308). The engine may feel like it’s “shaking” at idle.
- Hesitation and Power Loss: During acceleration, the engine may hesitate, stumble, or lack power due to incorrect ignition timing. You may notice a significant reduction in engine performance, especially under load.
- Poor Fuel Economy: Inefficient combustion resulting from improper timing reduces fuel efficiency. You may see a 10-25% decrease in miles per gallon.
- Illuminated Check Engine Light: The P0335 code will be stored, and depending on severity, may flash during active misfires. Some models may also display “Engine Malfunction” or “Reduced Power” messages.
- Failure to Remain Running After Start: The engine may start but immediately stall, as the ECM loses the crankshaft signal once the starter disengages.
Safety Warning: If your Mers experiences sudden stalling while driving, especially at highway speeds, it can create a dangerous situation. Have the vehicle inspected immediately if you notice any stalling behavior.
3.0 Root Causes of P0335 Code in Mers
Diagnosing the P0335 code requires a systematic approach to identify the underlying cause. The issue could be electrical, mechanical, or related to the sensor itself. Below are the most common causes with detailed explanations:
- Failed Crankshaft Position Sensor: Internal electronic failure due to heat, vibration, or age. Mers sensors typically last 80,000-120,000 miles. The sensor contains a magnetic element and coil that can degrade over time, or the integrated circuit can fail completely.
- Damaged Wiring or Connectors: Chafed, pinched, or cut wires in the sensor circuit. Common near connectors, engine movement points, or where wiring passes through brackets. Engine heat can also cause wire insulation to become brittle and crack over time.
- Corroded or Loose Connector: Moisture intrusion causing terminal corrosion, or connectors not fully seated, leading to intermittent connections. This is particularly common in vehicles driven in wet climates or those that have been through automatic car washes frequently.
- Damaged Reluctor Ring: The toothed wheel on the crankshaft (which the sensor reads) can have cracked, missing, or damaged teeth from impact, metal fatigue, or improper previous repairs. Even a single damaged tooth can cause intermittent P0335 codes.
- Excessive Sensor Air Gap: Incorrect installation, damaged mounting bracket, or debris between sensor and reluctor ring creating improper reading distance. The gap is typically 0.5-1.5mm and is critical for proper signal generation.
- Magnetic Interference: Aftermarket components or improperly routed wires creating electromagnetic interference with the sensor signal. High-current accessories installed near the sensor wiring can induce noise that corrupts the signal.
- Failed PCM/ECM: Rare, but possible internal processor failure preventing proper signal interpretation (requires professional diagnosis). This should only be considered after all other possibilities have been eliminated.
- Oil Contamination: Engine oil leaking onto the sensor can interfere with its operation, particularly for magnetic-type sensors where oil can attract metallic particles that disrupt the magnetic field.
4.0 Step-by-Step Diagnostic Procedure
A systematic approach to diagnosing P0335 will save time and money by ensuring you address the root cause rather than just replacing parts. Follow these steps in order:
4.1 Preliminary Safety and Visual Inspection
Tools Needed: Safety glasses, gloves, basic hand tools, flashlight
Time Estimate: 15-30 minutes
Skill Level: Beginner
- Park the vehicle on a level surface, set the parking brake, and disconnect the negative battery terminal to prevent electrical shorts or accidental engine start.
- Locate the crankshaft position sensor (refer to Mers service manual – typically near the main crankshaft pulley, transmission bell housing, or engine block). On most Mers models, it’s accessible from underneath the vehicle.
- Visually inspect the sensor mounting for damage, corrosion, or looseness. Ensure the sensor is securely fastened and properly positioned.
- Trace the sensor wiring harness back 12-18 inches, checking for:
- Chafing or rubbing against engine components, especially near moving parts
- Melting from exhaust contact – look for discolored or bubbled insulation
- Cracked or brittle insulation from heat aging
- Evidence of rodent damage – look for chew marks or nesting materials
- Previous repair attempts – poorly executed splices or electrical tape repairs
- Inspect the electrical connector for:
- Secure locking mechanism engagement – ensure it clicks when connected
- Corrosion on terminals (white/green deposits) indicating moisture intrusion
- Bent, pushed-out, or damaged pins that may not make proper contact
- Moisture intrusion or oil contamination inside the connector body
4.2 Electrical Testing Procedures
Tools Needed: Digital multimeter (DMM), back-probe pins, wiring diagram, Mers service manual
Time Estimate: 30-45 minutes
Skill Level: Intermediate
- Resistance Test (Sensor Disconnected):
- Set multimeter to resistance (Ohms Ω) at the appropriate scale
- Measure across sensor terminals (typical range: 200-1000Ω for magnetic sensors, 250-1500Ω for Hall-effect sensors)
- Compare to Mers specifications – significant deviation indicates sensor failure. No continuity (OL reading) indicates an open circuit in the sensor.
- Reference Voltage Check:
- Reconnect connector and back-probe the reference voltage wire (typically 5V or 12V – consult wiring diagram)
- With ignition ON, engine OFF, verify proper voltage. No voltage indicates wiring harness or ECM issue.
- Check for voltage drop by measuring between the reference voltage pin and battery positive while wiggling the harness.
- Ground Circuit Verification:
- Back-probe the ground wire with multimeter set to DC volts
- Measure voltage between ground terminal and battery negative – should read less than 0.1V with ignition ON
- Higher voltage indicates a poor ground connection that needs to be addressed
- Signal Output Test:
- Set multimeter to AC Volts scale (or use oscilloscope for best results)
- Back-probe the signal wire while assistant cranks engine – observe fluctuating AC voltage (typically 0.5V-5V)
- No signal indicates failed sensor or reluctor ring issue. Intermittent signal suggests wiring problems.
4.3 Reluctor Ring Inspection
Tools Needed: Inspection mirror, flashlight, borescope (recommended), socket set
Time Estimate: 20-60 minutes
Skill Level: Intermediate to Advanced
- Remove the crankshaft position sensor if necessary for visual access. Note the orientation for reinstallation.
- Using a borescope or inspection mirror, examine the reluctor ring teeth for:
- Cracks or physical damage to teeth – look for hairline fractures
- Missing teeth sections – even one missing tooth will cause problems
- Metal debris stuck to magnetic sensor area – clean thoroughly if found
- Excessive rust or corrosion affecting signal – particularly in older vehicles or those in coastal areas
- Build-up of metallic particles on magnetic sensors – clean with non-magnetic tool
- Slowly rotate engine (using socket on crankshaft pulley bolt) to inspect entire circumference of the reluctor ring.
- Check for proper alignment and mounting of the reluctor ring. It should be centered and securely attached to the crankshaft.
- If accessible, measure the air gap between the sensor mounting surface and reluctor ring using a feeler gauge. Compare to specifications (typically 0.5-1.5mm).
5.0 P0335 Repair Cost Estimation for Mers Vehicles
Repair costs for P0335 vary significantly based on the root cause, your Mers model, and whether you use OEM or aftermarket parts. Below is a detailed cost breakdown:
| Repair Scenario | Parts Cost | Labor Cost | Total Estimate | Complexity |
|---|---|---|---|---|
| Replace CKP Sensor Only Most common solution |
$75 – $200 OEM: $120-$200 Aftermarket: $75-$150 |
$100 – $250 0.5 – 1.5 hours |
$175 – $450 | Low |
| Repair Wiring Harness For damaged wires |
$25 – $75 Wire, connectors, loom, heat shrink |
$150 – $350 1 – 2.5 hours |
$175 – $425 | Moderate |
| Sensor Replacement + Wiring Repair Combination repair |
$100 – $275 Sensor + wiring materials |
$200 – $450 1.5 – 3 hours |
$300 – $725 | Moderate |
| Replace Reluctor Ring Major mechanical repair |
$80 – $300 Part only, varies by model |
$600 – $1,800 4 – 12 hours, transmission/engine removal |
$680 – $2,100+ | High/Complex |
| Complete Diagnosis (Professional) No repair, diagnosis only |
N/A | $100 – $200 Diagnostic fee, typically applied to repair |
$100 – $200 | Low |
| ECM/PCM Replacement Rare, last resort |
$800 – $1,500 New or reprogrammed unit |
$200 – $400 Programming and installation |
$1,000 – $1,900 | High/Complex |
Cost Variables to Consider
Note on Cost Variables: Luxury Mers models (S-Class, G-Class) typically incur 20-40% higher labor rates than entry-level models. Dealership repairs are generally 25-50% more expensive than independent specialists. Geographic location also significantly impacts labor rates ($85-$165/hour). Vehicles with all-wheel drive may require additional labor time for sensor access. Always request a detailed estimate before authorizing repairs.
6.0 Professional vs. DIY Repair Considerations
Deciding whether to attempt a P0335 repair yourself or seek professional help depends on several factors. Consider the following before making your decision:
When to Seek Professional Help:
- Diagnosis points to reluctor ring replacement (requires specialized tools and expertise)
- You lack electrical diagnostic experience or proper tools (multimeter, wiring diagrams)
- The vehicle is under warranty or service contract (DIY repairs may void coverage)
- Multiple error codes are present alongside P0335 (indicating a more complex issue)
- Previous DIY attempts have not resolved the issue (suggesting misdiagnosis)
- The sensor location requires significant disassembly to access
- You need the vehicle for daily transportation and cannot afford extended downtime
When DIY May Be Appropriate:
- You have intermediate automotive repair skills and proper tools
- Visual inspection reveals obvious sensor or wiring damage
- You have access to a quality scan tool, multimeter, and service information
- The sensor is easily accessible on your specific Mers model
- Vehicle is not your primary transportation (allowing time for troubleshooting)
- Budget constraints make professional repair difficult
- You enjoy learning about automotive systems and have time for proper diagnosis
7.0 Frequently Asked Questions (FAQ)
Not recommended. While some vehicles may run with a P0335 code, most will experience stalling, no-start conditions, or run very poorly. The risk of being stranded or causing further damage makes driving inadvisable. Have the vehicle towed to a repair facility if it’s not starting reliably. In rare cases where the vehicle is running, limit driving to essential trips only and avoid highways or high-speed roads.
P0335 indicates a complete circuit malfunction – no signal or implausible signal from the sensor. P0336 indicates the signal is present but out of expected range or erratic. P0336 often points to reluctor ring damage or sensor alignment issues, while P0335 typically indicates complete sensor failure or wiring problems. P0336 is generally easier to diagnose as the signal is present but incorrect.
Most Mers crankshaft position sensors last between 80,000 and 120,000 miles. However, they can fail earlier due to heat exposure, oil contamination, or electrical issues. Some models have known sensor reliability concerns, so checking Mers-specific forums for your model year is recommended. Proper installation and using OEM parts can extend sensor life.
Yes, disconnecting the battery will temporarily clear the code, but it will return almost immediately if the underlying problem isn’t fixed. The ECM continuously monitors the crankshaft sensor signal, so the code will reset once the fault is detected again (usually within one drive cycle). Clearing codes without diagnosis is not a repair strategy and can make intermittent issues harder to diagnose.
The reluctor ring is typically pressed onto the crankshaft, often requiring transmission removal or even engine disassembly to access. This labor-intensive process accounts for 80-90% of the total cost. Additionally, special tools may be needed to remove and install the ring without damaging the crankshaft. In some cases, the reluctor ring is integrated with the crankshaft, requiring complete crankshaft replacement.
While the sensor itself won’t directly damage the engine, the symptoms it causes potentially can. Incorrect timing from a faulty sensor can lead to pre-ignition, detonation, or misfires that may damage pistons, valves, or the catalytic converter. Additionally, sudden stalling can cause loss of power steering and brakes, creating dangerous driving situations. It’s best to address P0335 promptly to prevent potential collateral damage.
For critical sensors like the crankshaft position sensor, OEM parts are generally recommended. While more expensive, they’re designed specifically for your Mers model and have proven reliability. Aftermarket sensors can be hit-or-miss in terms of quality and longevity. If budget is a concern, choose a reputable aftermarket brand with a good warranty rather than the cheapest option available.
Final Recommendation from 24car-repair.com: The P0335 code requires proper diagnosis before parts replacement. Start with a thorough visual inspection, then proceed with systematic electrical testing. While sensor replacement is often the solution, don’t overlook wiring issues or the rare but costly reluctor ring damage. When in doubt, consult a professional Mers specialist to avoid unnecessary repairs and expenses. Proper diagnosis typically costs less than replacing parts without confirmation of failure.
