Most vehicles use a form of variable cam timing. Toyota has VVT, Honda has VTEC, and BMW VANOS, to name a few. These systems offer a range of benefits, from better fuel economy, performance, and smooth throttle curves. For these systems to work, the ECU needs to know the crankshaft position (engine speed).

To that end, a sensor is used to detect the camshaft position. This sensor is vital to the variable cam timing system’s function. When it malfunctions, the P0385 check engine light code is usually what your car will log. 

It’s one thing to know the trouble code, but another to diagnose what’s causing it and prevent any damage when it appears. This guide will show the causes, symptoms, and diagnostic techniques for the P0385 trouble code.

What is the P0385 Code, and What Does It Mean? 

A crankshaft translates the up-down motion of the pistons into a rotating motion. The P0385 code means that there is an issue with the crankshaft position sensor circuit. The full error message is “Crankshaft Position Sensor B Circuit Malfunction.” It specifically refers to circuit B of this sensor, which is the circuit for signal input from the sensor.

Where Is the Crankshaft Position Sensor Located?

The crankshaft position sensor is located either at the back or front of the crankshaft. It detects the movement of a reluctor wheel (sometimes flywheel) which is on the driveshaft. The location of this sensor means it will often require you to jack up your vehicle or get it up on the lift to properly diagnose it.

What Causes the P0385 Code?

The sensitivity of a crankshaft position sensor means the causes can vary. Tackling each one by one is the best way to pinpoint the root cause. Here are the most common causes:

• Wiring harness issues
• Malfunctioning crankshaft position sensor
• Failed reluctor ring

Wiring Harness Issues

Your wiring harness is the main carrier of voltage between the ECU and crankshaft position sensor. Any damage to the wiring harness can lead to a loss of voltage and faulty sensor readings. This can either stem from signal wire or voltage wire failure, but in the case of a P0385 code. 

Malfunctioning Crankshaft Position Sensor

Most modern crankshaft position sensors are hall effect sensors. These sensors are known for their reliability but can drift over time if exposed to heat. The location of the sensor means that this can become an issue if you drive your car on track or particularly hard.

Failed Reluctor Ring

A reluctor ring is a toothed ring mounted on the crankshaft that the sensor uses to detect the position of the crankshaft. Any damage to this ring means the sensor will no longer detect the position correctly. This can cause catastrophic damage or just the P0385 code.

In some cases, the magnetic sensor detects the crankshaft position using the flywheel. This is not common in modern cars as it can make diagnosis more difficult.

What Are the Common Symptoms of P0385 Fault Code?

The seriousness of this trouble code means that there are not many symptoms before your vehicle shuts down. However, there may be clear indicators of this code if you haven’t started your vehicle yet. Here are some common symptoms:

• Check engine light
• Poor starting behavior
• Cylinder misfires

Check Engine Light

The check engine light is a simple signal that something is wrong with your vehicle. With the P0385 code, your car will enter limp mode when the light turns on. This is to prevent any further damage that can be caused by a sensor failure.

Poor Starting Behavior

Variable cam timing is used to improve idle and starting. Of course, if your crankshaft position sensor malfunctions and your engine is tuned to operate using it, it may not even be able to start. Even if it can start, you may experience a rough idle or stalling as soon as you get going.

Cylinder Misfires 

Poor starting behavior goes along with misfiring cylinders due to poor cam timing. Of course, many issues can cause cylinders to misfire, so it’s not the most conclusive symptom. However, the P0385 can be caused by a cylinder misfire related to a crankshaft position sensor issue.

How to Diagnose and Fix the Cause of P0385 Code 

This section will walk you through each diagnostic process, from the tools to the methodology.

OBD-II Reader

An OBD-II reader is a perfect companion when diagnosing any car issue. Not only does it allow you to read error codes that the ECU logs, but it also lets you directly diagnose components using live data.

Plug your OBD-II reader into the connection port. This port is under the passenger-side dash. Once you’ve done that, scan for trouble codes and look for the P0385 code. Any additional crankshaft trouble codes are also important to look out for.

You can also use an OBD-II reader to read the live data coming from the crankshaft position sensor. You’re looking for an RPM signal because this sensor detects engine speed. Start your vehicle or attempt to crank it. You should get a consistent RPM reading on the OBD-II reader. It should also be the same as the rpm on the speedometer.

Visual Inspection

The location of a crankshaft position sensor can differ from vehicle to vehicle, so make sure you check your owner’s manual before completing this test. You should disconnect your battery as you will work under the vehicle for most of the diagnostic process.

Once you’ve found the sensor, look for any corrosion, dents, or whether the sensor is loose. If your wiring harness connector is frayed or there is any other damage to it, focus on that before you replace your sensor. If you find that it’s actually the sensor that’s causing the issue, get a quality one. Check our selection of crankshaft position sensors for reliable replacements.

Damage to your flywheel or reluctor ring can cause the P0385 code. It’s difficult to detect flywheel damage, as it is between the transmission and crankshaft and not accessible unless you disassemble the transmission. 

What you should look out for is the smell of a burned clutch. This is a sweet-tart apple smell and should be prominent when you inspect your engine. Any clutch issues or grinding when you attempt to start your vehicle are indicators of flywheel damage.

Of course, looking for reluctor ring damage is a similar process, but you may also look for chips or signs of scraping as the reluctor ring can be accessed from the bottom of the engine.

Wiring Harness Test

Inspecting your components is a great way to tell whether there is external damage. However, a compromised wiring harness may show no external signs of damage. 

A multimeter is a great tool to diagnose whether the wiring harness is damaged. Turn your multimeter to ohms as you will test for resistance.

Contact your red (positive) probe to the signal terminal and the black (negative) probe to the ground. The ground can be any piece of metal that has a route to the earth, even the vehicle chassis. You should get between 200 and 1000 ohms. Check your owner’s manual for a more specific resistance reading.

Crankshaft Position Sensor Test

For this test, we will use an oscilloscope to rule out whether the crankshaft position sensor is damaged. Contact your red oscilloscope probe to the sensor and the black probe to the chassis. You should get a clean 5-volt square wave on the screen.

Does P0385 Clear Itself?

Once you’ve fixed the issue causing the P0385, this code should clear itself within a drive cycle. As long as you don’t have a reluctor ring issue, it should be safe to start your vehicle and run it once you’ve completed the repair. As always, clearing the codes with an OBD-II reader is a good option as well.

Is It OK to Drive with P0385?

Most vehicles will enter limp mode when you experience a crankshaft position issue. However, some vehicle manufacturers allow your vehicle to continue running. Any cylinder misfires or abnormal sounds should be an indicator to stop your vehicle to prevent any further damage that an otherwise minor issue may cause. 

With that in mind, you should not drive your vehicle with the P0385 code.

Get Quality Crankshaft Position Sensors to Fix P0385 Code

Now you’ve run through all the causes, symptoms, and diagnostic processes. You’ve narrowed down the exact cause of the P0385. Fixing any trouble code is impossible without the correct replacement parts or tools. So you need the correct parts in record time.

Here at eEuroparts.com, we have what you need. Our comprehensive list of components allows you to pick the parts that you need for your vehicle. Just select your vehicle from the dropdown menu and the parts that you need. It’s that simple!