P0337 Crankshaft Position Sensor A Circuit Low Input: Causes, Symptoms & Fixes

Quick answer

• What the code means: The P0337 code means the engine control module (ECM) has detected that the signal from the crankshaft position sensor 'A' is lower than the manufacturer's specified range.
• Severity: Severe. Your vehicle may not start, could stall unexpectedly while driving, or run very poorly. It's recommended to stop driving as soon as possible.
• Most common cause: The most common cause of a P0337 code is a faulty crankshaft position sensor.

What the P0337 code means

The official OBD-II definition for P0337 is "Crankshaft Position Sensor 'A' Circuit Low Input." In plain English, this means your car's main computer, the ECM, is not receiving a strong or stable signal from the crankshaft position sensor (CPS). This sensor is critical for engine operation.

The crankshaft position sensor's job is to monitor the rotational speed and precise position of the engine's crankshaft. It sends this information to the ECM, which then uses it to control ignition timing and fuel injection. The sensor typically works with a reluctor wheel (a toothed ring) on the crankshaft. As the teeth pass the sensor, they create a voltage signal. A "low input" code means the voltage produced by the sensor is below the expected threshold, indicating a problem with the sensor itself or its electrical circuit.

Without an accurate signal from the CPS, the ECM doesn't know when to fire the spark plugs or inject fuel, leading to significant engine performance issues.

Common symptoms

If your vehicle has a P0337 code, you will likely notice one or more of the following symptoms:

• Engine will not start: This is the most common symptom. The ECM needs the CPS signal to initiate spark and fuel.
• Engine stalling: The engine may stall intermittently, especially when it warms up, and may not restart.
• Rough running / misfiring: The engine may idle poorly, hesitate on acceleration, or misfire.
• Check Engine Light (CEL) is on: The ECM will illuminate the Malfunction Indicator Lamp (MIL), also known as the Check Engine Light, to alert the driver of the fault.
• Reduced fuel economy: Improper ignition and fuel timing will cause the engine to use more fuel than necessary.
• Tachometer not working or behaving erratically: On some vehicles, the tachometer gets its reading from the crankshaft position sensor.

Common causes

Here are the most common causes of a P0337 code, ranked from most to least likely:

1. Faulty Crankshaft Position Sensor (CPS): This is the most frequent culprit. The internal electronics of the sensor can fail over time due to heat and vibration.
2. Wiring or Connector Issues: The wiring harness going to the CPS can become damaged, frayed, corroded, or shorted. The connector itself can also become loose, corroded, or filled with oil or other contaminants.
3. Damaged Reluctor Ring/Tone Wheel: The reluctor ring on the crankshaft can become damaged, bent, or have debris (like metal shavings) stuck to it, which will disrupt the signal.
4. Weak or Dying Battery: A low battery voltage can sometimes cause a low input code to be set.
5. Faulty Engine Control Module (ECM): This is the least likely cause, but the ECM can fail and incorrectly report a P0337 code. This should only be considered after all other possibilities have been exhausted.

How a technician diagnoses it

A technician will follow a systematic process to pinpoint the cause of a P0337 code. This typically involves:

1. Scan for Codes: The first step is always to connect a professional OBD-II scanner to verify the P0337 code is present and check for any other related codes. The technician will also look at the freeze-frame data, which is a snapshot of the engine's operating conditions at the moment the fault was triggered.
2. Visual Inspection: A thorough visual inspection of the crankshaft position sensor, its wiring harness, and connector is performed. The technician will look for any signs of damage, melting, corrosion, or loose connections.
3. Check the Sensor's Signal: Using an oscilloscope or a specialized scan tool with live data capabilities, the technician will monitor the output signal of the CPS. A good sensor will produce a clean, square wave pattern that changes with engine speed. A bad sensor might produce a weak, erratic, or nonexistent signal.
4. Test the Circuit: The technician will perform electrical tests on the circuit. This includes checking for correct voltage and ground at the sensor's connector using a digital multimeter (DMM). They will check for continuity and resistance in the wiring between the sensor and the ECM to rule out an open or shorted wire.
5. Inspect the Reluctor Ring: If the sensor and wiring check out, the technician may need to visually inspect the reluctor ring for damage. This can be difficult as it often requires removing other engine components for access.
6. Test with a New Sensor: If all other tests are inconclusive, a known-good sensor may be temporarily installed to see if the code disappears and the symptoms are resolved.
7. ECM Testing: As a final and rare step, if all else fails, the ECM's driver circuit for the CPS will be tested.

Typical repair cost

The cost to repair a P0337 code can vary significantly based on the vehicle make and model, and the specific cause.

• Parts:

  • Crankshaft Position Sensor: $20 - $150

• Labor:

  • Diagnosis: $100 - $200 (typically a 1-1.5 hour diagnostic fee)
  • Sensor Replacement: $75 - $300 (Labor time can range from 30 minutes to over 2 hours depending on sensor location).

• Total Cost: For the most common repair—replacing the crankshaft position sensor—you can expect to pay between $120 and $450. If the issue is simply a loose connection, the cost could be as low as the diagnostic fee. If the reluctor ring is damaged or the ECM needs replacement, the cost will be significantly higher.

Can I keep driving with this code?

No, it is not recommended to continue driving with a P0337 code. The primary risks are that the engine could stall at any time, including in traffic or at high speeds, creating a serious safety hazard. You could also be left stranded if the engine fails to start at all. Driving with this code can also cause further damage to other engine components. Get the vehicle inspected and repaired as soon as possible.

Related codes

• P0335: Crankshaft Position Sensor 'A' Circuit Malfunction
• P0336: Crankshaft Position Sensor 'A' Circuit Range/Performance
• P0338: Crankshaft Position Sensor 'A' Circuit High Input
• P0339: Crankshaft Position Sensor 'A' Circuit Intermittent
• P0385: Crankshaft Position Sensor 'B' Circuit Malfunction

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