Mercedes-Benz ML320 Engine Crankshaft Position Sensor: A Complete Guide (1998-2009)
If your ML320 stalls when it gets warm or refuses to start, the crankshaft position sensor is the most likely culprit.
- The most common symptom of failure is the engine stalling when hot and refusing to restart until it cools down.
- For reliable results, use only a Bosch brand sensor, which is the original equipment manufacturer (OEM).
- This is a common DIY repair that can be done with basic tools, but access is tight, especially on the V6 gas engine.
- A recall was issued for the 2007 ML320 CDI diesel model for this specific issue; check your VIN's recall status.
Understanding the ML320 Model Years
It is important to know which ML320 you own, as the engine and sensor location are different. This guide covers both.
- 1998-2003 ML320 (Gasoline V6): This model uses the M112 V6 gasoline engine. The crankshaft sensor is a very common failure item on these.
- 2007-2009 ML320 CDI (Diesel V6): This model uses the OM642 V6 turbo-diesel engine. The sensor location and part number are different from the gasoline version.
Recall Information for 2007 ML320 CDI
There was a recall issued by the NHTSA for the 2007 Mercedes-Benz ML320 CDI. The recall addressed a faulty crankshaft sensor that could fail, leading to a sudden loss of engine power and stalling. If you own a diesel model from this year, it is crucial to check with a Mercedes-Benz dealer or use the official NHTSA website to see if your vehicle was affected or serviced.
Symptoms of a Failing Crankshaft Position Sensor
A bad crankshaft sensor has very distinct symptoms. The most common issue is heat-related failure. The sensor works when the engine is cold but fails as it heats up.
- Engine Stalls When Hot: The number one symptom. The engine runs fine, but after 15-30 minutes of driving, it will suddenly stall.
- No-Start When Hot: After stalling, the engine will crank but will not restart. You may have to wait 10-30 minutes for the engine to cool down before it will start again.
- Check Engine Light: A failing sensor will almost always trigger the Check Engine Light. The most common diagnostic trouble code (DTC) is P0335 (Crankshaft Position Sensor 'A' Circuit Malfunction).
- Rough Idle and Misfires: The engine may run rough, vibrate, or feel like it's stumbling.
- Poor Acceleration: Your ML320 may feel sluggish and unresponsive when you press the gas pedal.
Choosing the Right Aftermarket Sensor
For many electronic parts on a Mercedes-Benz, the brand you choose matters significantly. This is especially true for the crankshaft position sensor. A cheap, low-quality sensor can fail quickly, leaving you stranded again.
Brand Tiers
- Tier 1 - OEM / Recommended: Bosch is the Original Equipment Manufacturer (OEM) for this part on the M112 gas engine. This means it's the same part you would get from a Mercedes-Benz dealership, just in a different box. For reliability and peace of mind, Bosch is the best choice.
- Tier 2 - Reputable Aftermarket: Brands like Hella and Delphi are generally considered reputable. However, forum discussions suggest that for this specific, critical sensor, the small savings are not worth the risk compared to using the proven OEM Bosch part. Some users report fitment or early failure issues with non-Bosch brands.
- Tier 3 - Budget Brands to Avoid: It is strongly recommended to avoid unknown or store-brand sensors. Forum users frequently report that these parts are often dead-on-arrival or fail within a few weeks or months. The labor to replace it again outweighs any initial savings.
Pro Tip: Stick with Bosch
The overwhelming consensus from Mercedes-Benz mechanics and owners is to use only the Bosch sensor for this repair. The price difference is minimal, but the difference in reliability is significant.
Replacement Overview
Replacing the sensor is a common DIY job for many ML320 owners. Access is tight, but it does not require complex procedures.
- Gasoline ML320 (M112): The sensor is on the driver's side, at the back of the engine where it connects to the transmission. It is held in by a single E8 Torx bolt. Access is tight, and it's often done by feel. You will need a 1/4-inch drive ratchet with long extensions and an E8 female Torx socket.
- Diesel ML320 CDI (OM642): The sensor is also at the back of the engine. Access requires removing the engine cover and the passenger-side air filter housing assembly. The job requires E10 and E11 Torx sockets.
| Part Type | Estimated Cost |
|---|---|
| New OEM (Dealer) | $110 - $160 |
| New Aftermarket (Bosch - Recommended) | $45 - $87 |
| New Aftermarket (Other Brands) | $24 - $60 |
| Shop Labor | $73 - $107 |
Frequently Asked Questions
Where is the crankshaft sensor located on my ML320?
On the 1998-2003 gasoline V6, it's on the driver's side of the bell housing at the rear of the engine. On the 2007-2009 diesel V6, it's in a similar area but requires removing the passenger-side air filter box for access.
Can I replace this sensor myself?
Yes, this is a very popular DIY repair. The main challenge is the tight access space, not the complexity of the task. You will need an E8 (for gas) or E10 (for diesel) external Torx socket and long extensions. Always work on a cold engine to avoid severe burns.
Why did my cheap aftermarket sensor fail so quickly?
Low-quality sensors often use inferior materials and electronics that cannot withstand the high heat at the back of the engine bay. This is why they fail quickly, often exhibiting the same heat-related stalling as the original failed part. This is why sticking to the OEM Bosch brand is highly recommended.
Do I need to reset the computer after replacing the sensor?
Once the new sensor is installed, the car should start and run correctly. The Check Engine Light may turn off on its own after a few drive cycles, or you can clear the P0335 code with a standard OBD-II scanner.
Technical Specifications
OEM Part Numbers: A0031532828 A0031532728 A6429050000
The sensor for the gasoline M112 engine is a 2-pin inductive sensor held by one E8 Torx bolt. The sensor for the diesel OM642 engine is a 3-pin Hall effect sensor held by one E10 Torx bolt.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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