P0337 Error Code: Symptoms, Causes, Diagnosis, and How to Fix It

1. Introduction

P0337 Error Code There is an unspoken language between a driver and their car. You turn the key or press the start button, and you instantly expect that familiar, rhythmic hum of the internal combustion engine coming to life. But when that rhythm breaks—replaced by a starter motor that cranks endlessly without catching, or an engine that violently stumbles and dies at a busy intersection—that bond of trust is instantly severed. Suddenly, a bright amber check engine light pierces through your instrument cluster. If you have plugged an OBD2 scanner into your vehicle’s diagnostic port and found yourself staring at the P0337 error code, your car’s engine control module (ECM) is essentially telling you that it has lost its most vital sense of direction.

An internal combustion engine is a masterclass in split-second synchronization. For a motor to run smoothly, pistons move up and down, valves open and close, and spark plugs fire at intervals measured in fractions of a millisecond. To coordinate this complex mechanical ballet, the vehicle’s central computer must know the exact position and rotational speed of the crankshaft at all times. When the signal that carries this crucial data drops below an acceptable electrical threshold, the entire system falls into complete disarray. The engine becomes like an orchestra whose conductor has suddenly walked off the stage.

Dealing with the P0337 error code can be incredibly frustrating, especially because its real-world symptoms can range from a minor drop in fuel economy to a completely immobilized vehicle stranded on the side of the road. However, understanding what is happening under the hood can save you from unnecessary stress and expensive, misdiagnosed repairs at local repair shops. In this comprehensive guide, we will break down the engineering behind this specific fault code, explore the physical symptoms you should watch out for, isolate the root causes, and walk through a professional, step-by-step diagnostic routine to get your car back on the road safely.

2. What is the P0337 Error Code?

To truly grasp the mechanics of the P0337 error code, we need to translate its official automotive definition: “Crankshaft Position (CKP) Sensor ‘A’ Circuit Low Input.” In this specific diagnostic context, the letter “A” refers to the primary crankshaft position sensor or the main circuit dedicated to monitoring the engine’s lower rotating assembly. The term “Low Input” is the most critical piece of the puzzle. It indicates an electrical reality where the voltage signal arriving at the engine control module (ECM) remains consistently below the minimum parameters established by the manufacturer’s factory software.

The crankshaft position sensor operates as an electromagnetic watchman. Positioned directly adjacent to a reluctor wheel—a specialized metallic ring with a precise pattern of teeth attached to the spinning crankshaft—the sensor continuously monitors these passing teeth. As the crankshaft rotates, the teeth disrupt the magnetic field generated by the sensor, producing a distinct electrical signal. This signal is typically an alternating current (AC) sine wave in older variable reluctance sensors, or a digital square wave in modern Hall-effect configurations. The computer counts these voltage pulses to calculate the exact engine revolutions per minute (RPM) and determines exactly when the number one cylinder reaches Top Dead Center (TDC).

The P0337 error code is fundamentally different from other related crank codes. For instance, while a P0335 code frequently denotes a total electrical open circuit where the sensor is completely dead, and a companion code like the P0336 represents an erratic signal that is merely out of range, the P0337 error code explicitly points to a weak, severely attenuated, or shorted-to-ground voltage pattern. The ECM knows a sensor is connected, but the incoming electrical pulses are so weak, flatlined, or low in voltage that the computer cannot confidently use them to manage fuel injection pulses or ignition coil timing sequences.

3. Symptoms / What Will You Notice?

When the P0337 error code triggers within your vehicle’s onboard diagnostics, the car does not quietly suffer in silence. Because the crankshaft signal directly dictates the fundamental behavior of both the ignition and fuel systems, a low-input voltage failure will present itself through a series of unmistakable, frustrating, and sometimes intimidating physical driving symptoms:

• Illumination of the Check Engine Light: The most immediate indication is the yellow or red malfunction indicator lamp (MIL) on your dashboard. Depending on how low the voltage drops during specific driving intervals, this light may stay permanently lit or flash during hard acceleration. For a broader look at why these indicators behave this way, checking our guide on why is my check engine light on can offer valuable background.
• Extended Cranking or Failure to Start: Because the ECM requires a clean, high-amplitude voltage spike from the crankshaft sensor during initial startup to authorize spark and fuel delivery, you will likely notice your engine cranking for 5 to 10 seconds before starting. In severe cases of a total short to ground, the vehicle will experience a complete “no-start” condition. P0337 error code
• Sudden Engine Stalling While Driving: This is undoubtedly the most dangerous symptom associated with a failing CKP sensor circuit. If the signal drops below the required voltage threshold while you are traveling at highway speeds, the ECM will instantly lose its tracking capabilities and cut fuel delivery for safety, causing the engine to shut off unexpectedly.
• Severe Engine Misfires and Hesitation: If the voltage signal is weak but still barely readable, the engine timing will continuously drift backward and forward. This causes erratic combustion inside the cylinders, which drivers experience as a violent jerking or stumbling when trying to accelerate. If you suspect this is happening, reviewing the details on engine misfiring symptoms causes solutions can help clarify the connection.
• Rough and Unstable Idle: When your vehicle is idling at a red light, you may notice the RPM gauge needle bouncing up and down erratically. The engine may shake noticeably, vibrating the steering wheel and cabin floor as the computer struggles to maintain stable idle control.
• Noticeable Loss of Engine Power: When the ECM detects a low-voltage input from the crankshaft circuit, it often switches into a default protective operating program known as “limp mode.” This deliberately limits engine power, disables turbocharger boost or variable valve timing, and prevents the transmission from shifting into higher gears to protect the mechanical internals.
• Poor Fuel Economy: When combustion timing is uncoordinated, fuel is frequently sprayed at the wrong time, leading to incomplete combustion. This unburnt fuel is wasted out the exhaust system, noticeably increasing your weekly fuel costs and potentially triggering secondary emission faults over time.

4. Common Causes

The P0337 error code is rarely a localized issue that only points to a defective sensor. Because it is explicitly an electrical circuit code, any physical component, wiring connection, or mechanical deviation that reduces the voltage potential between the sensor and the computer can serve as the primary catalyst. The most frequent causes include: P0337 error code

1. Short Circuit to Ground in the Signal Harness: The most common driver of a “low input” code is a physical breach in the wiring insulation. If the delicate signal wire running from the sensor to the ECM rubs against a sharp metal bracket on the engine block, the voltage will bypass the computer and drain straight to the chassis ground, resulting in a near-zero voltage reading.
2. Defective Crankshaft Position Sensor: Internal component degradation within the sensor itself can cause a drop in electrical resistance. As a magnetic pickup sensor ages, its internal copper wire windings can short-circuit when exposed to extreme engine bay heat, dramatically lowering the output voltage amplitude.
3. Corroded, Loose, or Oil-Soaked Connectors: Located low on the engine block, the crankshaft sensor connector is constantly bombarded by road debris, water splash, and engine oil leaks. If oil creeps past the weather seals into the terminal pins, it acts as an insulator or creates a high-resistance bridge that severely degrades the incoming voltage signal. P0337 error code
4. Excessive Sensor-to-Reluctor Wheel Air Gap: If the crankshaft sensor was poorly installed during a previous repair, or if its mounting bolt has backed out due to engine vibration, the physical distance between the sensor tip and the reluctor wheel teeth increases. Because magnetic strength drops exponentially with distance, a wider gap results in a critically low voltage signal.
5. Damaged or Deformed Reluctor Ring Dihes: If the engine has suffered mechanical trauma, or if debris has somehow entered the timing cover area, the teeth on the reluctor wheel can become chipped, bent, or filled with magnetic metallic shavings. This prevents the sensor from generating a strong magnetic field disruption. P0337 error code
6. Stretched Timing Chain or Faulty Belt Tensioners: If there is excessive slack in the mechanical timing components, the relationship between the crankshaft and camshaft becomes unaligned. This mechanical delay can cause the ECM to flag a low performance/input error because the expected signals do not align with internal engine phase maps, sometimes mirroring a complex P0300 random misfire condition.
7. Faulty Engine Control Module (Rare): While uncommon, the internal processing circuit or hardware pin inside the ECM responsible for pulling up the reference voltage can fail. If this internal circuit degrades, it will read a low input regardless of how well the external sensor is performing. P0337 error code

5. How Serious Is It?

The P0337 error code carries a very high severity rating and demands your immediate diagnostic attention. It is absolutely not an issue that you should ignore or postpone while continuing your normal daily commute. The most pressing concern with a low-input crankshaft circuit is the total unpredictability of when the engine might completely shut off. Stalling unexpectedly while driving at high speeds on an open expressway or trying to cross a multi-lane intersection places you, your passengers, and other drivers in immediate danger. When an engine stalls while in motion, you instantly lose your power steering assistance and your brake booster loses its vacuum reserve, making the vehicle incredibly heavy and difficult to maneuver safely to the shoulder. P0337 error code

From a purely mechanical standpoint, operating a vehicle with a degraded and failing crankshaft signal can cause severe collateral damage to your powertrain. When the timing of the spark plug detonation is incorrect, it can cause an engine phenomenon known as pre-ignition or detonation (engine knocking). This creates massive, uncoordinated pressure waves inside the combustion chamber that can physically crack piston rings, bend connecting rods, or blow out head gaskets. P0337 error code

Furthermore, the raw, unburnt gasoline resulting from these timing errors travels straight down into your hot exhaust tract. This raw fuel will ignite inside the delicate precious metal matrices of your emissions system, causing them to overheat, melt, and completely fail. Ignoring a simple electrical wiring issue can quickly cascade into a costly multi-thousand-dollar repair bill that involves replacing highly sensitive components or undergoing a complete engine rebuild. P0337 error code

6. How to Diagnose?

Properly diagnosing the P0337 error code requires a methodical approach that rules out simple wiring and mounting flaws before you rush to purchase replacement parts. Following this structured diagnostic routine will ensure you locate the exact root cause of the low-input fault:

Step 1: Scan for Codes and Examine Freeze Frame Data

Connect your professional OBD2 scan tool to the diagnostic port under the dashboard. Read all active, pending, and permanent trouble codes. Pay close attention to whether the P0337 code is accompanied by related electrical system faults or camshaft synchronization errors. Next, extract the freeze frame data to analyze the engine environment when the code occurred. Did the low voltage manifest at a cold idle, or did it happen while cruising at 3,000 RPM? P0337 error code

Step 2: Thorough Physical Inspection of the Harness

Locate the crankshaft position sensor on your specific engine block (it is typically found near the main crank pulley at the front, or low down near the flywheel housing at the back). Carefully trace the wiring harness back from the sensor toward the main engine loom. Inspect every inch for signs of heat damage, melting against exhaust manifolds, insulation chafing against metal edges, or wires that have been stretched taut by engine movement. P0337 error code

Step 3: Inspect the Sensor Connector and Terminals

Disconnect the electrical plug from the CKP sensor. Look inside both the male and female ends of the plug using a bright inspection light. Check for the presence of engine oil, green copper corrosion, or moisture intrusion. Tug gently on the individual wires to ensure the internal metal pins haven’t broken free from their crimps inside the plastic connector housing. If the plug is saturated with engine fluid, it must be thoroughly decontaminated. P0337 error code

Step 4: Check Sensor Mounting and Air Gap

P0337 error code Ensure that the sensor is sitting perfectly flush against its mounting surface on the engine block and that the retaining bolt is torqued down to factory specifications. If the sensor is loose, or if an incorrect aftermarket sensor without the proper depth profile was installed, the air gap will be too wide, directly creating the low-input condition.

Step 5: Electrical Voltage and Continuity Testing with a Multimeter

Set your digital multimeter (DMM) to the DC Volts setting to test the circuit integrity.

• Reference Voltage: Turn the vehicle’s ignition to the “ON” position without cranking the engine. Test the power wire at the sensor connector to ensure the ECM is sending a stable 5-volt or 12-volt reference signal (depending on vehicle design).
• Ground Circuit: Switch your meter to the Continuity/Ohm setting and test the ground wire between the connector and a clean chassis ground. It should read very close to 0 Ohms.
• Signal Wire Short to Ground: Disconnect the ECM connector and check for continuity between the signal wire and a chassis ground. If your meter beeps or shows low resistance, the signal wire is physically shorted to ground somewhere within the harness, which perfectly explains the low-input code. P0337 error code

Step 6: Live Signal Waveform Analysis with an Oscilloscope

For the most accurate assessment of a performance-based code like P0337, connect a digital storage oscilloscope to the back-probed signal wire while the engine is running or cranking. A healthy sensor should display a crisp, uniform wave pattern with consistent peak-to-peak voltage heights. If the waveform appears flattened, barely registers above zero volts, or shows dropped pulses at specific intervals, the sensor’s internal magnetic core has failed, or you are dealing with a heavily damaged reluctor wheel.P0337 error code

7. How to Fix It?

Once your systematic testing has isolated the broken link in the crankshaft monitoring chain, you can implement the corresponding repair procedure to permanently clear the P0337 error code:

• Replacing the Crankshaft Position Sensor: If your multimeter or oscilloscope testing indicates that the sensor itself is internal shorting or failing to generate the necessary voltage amplitude, it must be replaced. When performing this repair, always opt for an original equipment manufacturer (OEM) or high-quality name-brand component. Cheap, unbranded aftermarket sensors often exhibit poor electrical resistance properties out of the box, which can trigger a recurrence of the code within a few hundred miles.
• Repairing Shorted or Damaged Signal Wiring: If you locate a section of wiring where the insulation has rubbed away and exposed bare copper, cut out the compromised segment. Solder a new piece of automotive-grade wire of the identical gauge into place, and seal the connection securely with marine-grade heat-shrink tubing to keep out moisture. Never rely on basic electrical tape for sensitive sensor circuits.
• Cleaning or Replacing the Connector Plug: If the connector plug is filled with oil or showing signs of pin corrosion, spray it thoroughly with an electronic contact cleaner and brush away any debris. If the plastic locking tab is broken or the pins are loose, cut the old pigtail connector off and splice a new replacement harness plug into place. P0337 error code
• Correcting the Sensor Air Gap or Reseating: If the sensor was simply loose or crooked, remove it entirely, clean its mounting bore hole of any rust or dirt buildup, reinsert it so it seats perfectly flush, and torque the retaining bolt down properly to bring the sensor tip back within the correct physical distance from the reluctor wheel.
• Reluctor Wheel Remediation or Replacement: If you discovered that the reluctor wheel has debris stuck in its teeth, carefully clean the ring through the sensor port. However, if teeth are bent or broken, the reluctor wheel must be replaced. This is a highly intensive mechanical procedure that often requires removing the front timing assembly or separating the transmission from the engine block.
• Clearing the Error Code and Road Testing: After completing your repairs, reconnect your OBD2 scanner and manually clear the stored P0337 trouble code from the ECM memory. Start the vehicle and let it reach full operating temperature. Then, execute a comprehensive road test that spans both low-speed city driving and high-speed highway cruising to verify that the check engine light remains completely off and the signal stays stable.
• P0337 error code

8. Repair Cost

The overall financial cost to resolve a P0337 error code can vary significantly based on whether your issue stems from a simple loose connection, a failed sensor body, or a deep mechanical timing misalignment. To help you budget effectively, here is a detailed breakdown of the average parts and labor costs you can expect to encounter at a professional automotive repair shop:

Disclaimer: The financial figures listed in this table are baseline industry estimates. Actual costs will vary depending on your specific vehicle make and model, your geographic location, and local shop labor rates. P0337 error code

9. Related Issues

When your vehicle struggles with an electrical circuit failure as foundational as the P0337 error code, it rarely exists completely in a vacuum. The erratic or missing electrical data often triggers a chain reaction across other onboard systems, leading to a variety of interconnected diagnostic trouble codes and mechanical driving issues. P0337 error code

For instance, because the engine control module cannot accurately verify exactly when each cylinder reaches the top of its compression stroke, it will often begin firing the spark plugs at incorrect intervals. This directly leads to an irregular power balance, which frequently triggers a P0300 random misfire code or causes targeted single-cylinder combustion failures such as the P0301 code or P0302 code configurations.

Additionally, a low input on the crankshaft circuit can severely disrupt how the vehicle’s computer monitors fuel delivery parameters. If the timing becomes slightly retarded or delayed, the engine may draw in more unmetered air relative to the amount of fuel injected, causing the vehicle to flag a P0171 lean system error. P0337 error code

Over a longer timeline, if you continue to drive the vehicle while experiencing these uncoordinated combustion cycles, the resulting raw, unburnt gasoline escaping into your exhaust manifold will cause catastrophic thermal stress to your emission controls. This will rapidly degrade your catalytic converters, eventually forcing your vehicle to flag an expensive P0420 catalyst efficiency code.

10. Frequently Asked Questions

Can I drive my car with a P0337 error code active?

No, you should not continue to drive your car with an active P0337 code. Because this code signifies that the crankshaft position sensor circuit voltage is critically low, the signal could cut out entirely at any moment. This poses a major safety risk if the engine suddenly stalls while you are moving in heavy traffic or traveling at high highway speeds. P0337 error code

What is the primary difference between P0335, P0336, and P0337?

The P0335 code typically indicates a fundamental electrical failure where the ECM detects no signal or a total open circuit. The P0336 code means a signal is present but it is erratic, noisy, or dropping pulses out of its expected range. The P0337 code explicitly means that the signal wire voltage is staying below the required minimum threshold, which is usually caused by a short circuit to ground or a heavily degraded sensor core.

Can a bad car battery cause a P0337 error code?

Yes, a severely weak or dying car battery can sometimes cause a P0337 code to trigger. When you attempt to start an engine with a weak battery, the voltage across the vehicle’s electrical system can drop significantly during cranking. If the system voltage drops below 9 volts, the ECM may flag a low-input code simply because it didn’t have enough electrical power to read the sensor correctly.

Where is the crankshaft position sensor typically located?

The exact location depends heavily on your vehicle’s engine layout, but it is almost always located low down on the engine block near the rotating center line. On many front-wheel-drive vehicles, it is positioned near the main crankshaft harmonic balancer pulley at the front of the engine. On other rear-wheel-drive configurations, it may be mounted at the back of the engine block, reading a reluctor wheel built onto the transmission flywheel. P0337 error code

Why does my engine only stall once it gets hot when this code is present?

This is a classic symptom of an internal sensor winding failure. As the engine runs, heat builds up inside the sensor casing. This thermal expansion causes the ultra-fine copper wires inside the sensor’s electromagnet to expand. If the wire insulation has degraded, this heat expansion causes the wires to touch each other and short out internally, dropping the output voltage and triggering the P0337 code until the engine cools back down.

Will changing the crankshaft sensor always fix the P0337 code?

Not necessarily. While a bad sensor is a very common culprit, the P0337 code is explicitly a circuit code. If the signal wire running between the sensor plug and the computer is rubbed bare and shorting against the engine block, replacing the sensor will not solve the issue. You must test the entire wiring harness and check the physical condition of the reluctor wheel teeth to ensure a permanent fix.

Can a bad camshaft sensor trigger a P0337 code?

A bad camshaft sensor will usually trigger its own specific diagnostic trouble codes (such as P0340 or P0341). However, because the ECM constantly compares the crankshaft position signal against the camshaft position signal to verify proper engine timing synchronization, a massive timing chain stretch or jump that misaligns both sensors can sometimes trick the computer into setting a P0337 performance or circuit code. P0337 error code