P0335 Crankshaft Position Sensor "A" Circuit Malfunction

P0335 means the engine control module (ECM/PCM) has detected a malfunction in the Crankshaft Position Sensor “A” circuit.

The crankshaft position sensor is one of the most important sensors in the engine management system. It provides the ECM with information about crankshaft position and engine speed, which the computer uses to determine when fuel should be injected and when ignition should occur.

The important point with P0335 is that the code does not automatically mean the crankshaft position sensor itself is defective.

The actual problem can be the sensor, its power supply, ground, wiring, connector, reluctor/trigger wheel, sensor installation, or, less commonly, the ECM.

What Does the Crankshaft Position Sensor Do?

The crankshaft position sensor monitors the rotation of the crankshaft and sends a corresponding electrical signal to the ECM.

The ECM uses this information to determine:

• Engine RPM

• Crankshaft position

• Piston position

• Ignition timing

• Fuel injection timing

• Engine synchronization

• Misfire detection

• VVT control strategies

The crankshaft signal is effectively one of the engine's primary timing references.

If the ECM cannot obtain a valid crankshaft signal, it may not know exactly when the engine is rotating or where the crankshaft is positioned.

This is why a P0335 fault can produce anything from a Check Engine Light with no obvious drivability problem to a complete crank-no-start condition.

What Does “Sensor A” Mean?

“Sensor A” is a manufacturer-specific designation.

On many engines there is only one crankshaft position sensor, so identifying Sensor A is straightforward.

However, the exact sensor configuration varies between engines.

The physical location and circuit should therefore be confirmed using the manufacturer's wiring diagram and service information rather than relying solely on the generic OBD description.

What Does “Circuit Malfunction” Mean?

P0335 is a relatively broad code.

Unlike:

• P0337 – low input

• P0338 – high input

• P0339 – intermittent

P0335 does not specify exactly how the signal has failed.

The ECM has determined that the crankshaft sensor circuit is not functioning as expected, but the reason can be electrical, signal-related, or sometimes associated with the sensor's mechanical target.

The code therefore needs further testing before a component is replaced.

Common Causes of P0335

Faulty crankshaft position sensor

The sensor itself can fail internally and stop producing the expected signal.

Failure may be:

• Complete

• Intermittent

• Temperature dependent

• RPM dependent

• Vibration dependent

A sensor can sometimes work perfectly when the engine is cold and fail once it reaches operating temperature.

Damaged wiring

The wiring between the sensor and ECM can develop:

• Open circuits

• Short circuits

• Excessive resistance

• Broken conductors

• Chafed insulation

• Corroded connections

• Poor previous repairs

Because crankshaft sensors are often mounted close to the engine, the wiring can be exposed to significant heat, oil, vibration and movement.

Poor connector contact

A loose terminal or corroded connector can interrupt the crankshaft signal.

This can be especially difficult to find because the connector may look normal from the outside.

A terminal can have insufficient contact pressure even though there is no obvious physical damage.

Sensor power supply problem

Some crankshaft position sensors require an external power supply.

If that voltage is missing or incorrect, the sensor may not produce the expected output.

The exact circuit depends on the sensor design.

Poor ground

A sensor with a poor ground may produce an incorrect or missing signal.

Ground circuits should be tested under operating conditions because a simple continuity test does not always reveal excessive resistance.

Damaged reluctor or trigger wheel

The crankshaft sensor reads a physical target attached to the crankshaft or associated rotating assembly.

This target may be called a:

• Reluctor

• Tone wheel

• Trigger wheel

• Pulse wheel

If the target is damaged, loose, contaminated, or incorrectly positioned, the sensor may be unable to generate the expected signal.

Incorrect sensor air gap

On some sensor designs, the distance between the sensing element and reluctor is critical.

If the sensor is incorrectly installed or the mounting position has changed, the signal may become too weak or disappear.

Metal contamination

Magnetic crankshaft sensors can sometimes become contaminated with metallic debris.

Excessive debris around the sensing element can interfere with the signal.

This depends on the sensor design, so it should not be assumed to apply to every engine.

Mechanical crankshaft problem

Excessive crankshaft movement, damaged components, or another mechanical fault can change the relationship between the sensor and reluctor.

This can result in an apparently electrical sensor problem.

ECM/PCM fault

The ECM's crankshaft signal input circuit can fail internally.

However, this is considerably less common than a sensor, connector, wiring, or mechanical target problem.

The ECM should therefore be considered only after the external circuit has been thoroughly tested.

Symptoms of P0335

The symptoms depend on how the engine management system responds to the missing or incorrect crankshaft signal.

Possible symptoms include:

• Check Engine Light

• Hard starting

• Extended cranking

• Crank-no-start

• Intermittent no-start

• Engine stalling

• Rough running

• Misfires

• Hesitation

• Poor acceleration

• Sudden loss of power

• Abnormal tachometer behavior

• Reduced engine performance

A vehicle with P0335 may sometimes drive normally.

That does not necessarily mean the problem is minor.

If the crankshaft signal fails suddenly while driving, the engine can stall without warning.

Why Can P0335 Prevent the Engine From Starting?

During cranking, the ECM needs to know that the crankshaft is rotating and where it is positioned.

The starter can physically turn the engine even when the ECM is receiving no valid crankshaft signal.

This creates the classic:

engine cranks normally but does not start

situation.

Without a reliable crankshaft position reference, the ECM may be unable to determine the correct timing for ignition and fuel injection.

Some systems may also disable fuel injection or ignition when a valid crankshaft signal is absent.

This is why a crankshaft position problem can be much more serious than many other sensor faults.

Can the Engine Run Without a Crankshaft Sensor Signal?

In most modern engine management systems, the crankshaft position signal is fundamental.

Some systems may temporarily operate using alternative information or a backup strategy under particular circumstances, but the crankshaft signal is normally essential for accurate engine synchronization.

If the signal is completely lost, the engine will often stall or fail to start.

This is different from some camshaft sensor failures where the ECM can sometimes continue operating using the crankshaft signal.

Hall-Effect vs Variable-Reluctance Sensors

The correct diagnostic procedure depends on the sensor type.

A Hall-effect crankshaft sensor normally receives an external power supply and produces a digital switching signal.

A variable-reluctance (VR) sensor generates an AC voltage as the crankshaft reluctor passes the sensing element. The signal amplitude changes with engine speed.

Because these systems work differently, there is no universal voltage or resistance specification for P0335.

A resistance value that is normal for one sensor may be meaningless for another.

Always use the specifications for the particular engine.

How to Diagnose P0335 Correctly

The goal is to determine why the ECM cannot obtain a valid crankshaft signal.

Replacing the sensor immediately is often tempting, especially because the sensor is relatively inexpensive on many vehicles. But if the real problem is wiring or the trigger wheel, the new sensor will not solve the fault.

1. Scan all stored and pending codes

Start with the complete diagnostic picture.

Look for:

• P0336

• P0337

• P0338

• P0339

• Camshaft position codes

• Cam/crank correlation codes

• VVT codes

• Misfire codes

• Low-voltage codes

Additional codes can help determine whether the problem is isolated to the crankshaft sensor circuit.

Freeze-frame information is also valuable because it can show engine RPM, coolant temperature and other operating conditions when the fault was detected.

2. Check whether the ECM sees engine RPM during cranking

This is a useful diagnostic clue.

When the engine is cranking, observe the RPM parameter with a scan tool.

If the engine is physically turning but the ECM reports 0 RPM, the crankshaft signal should be investigated closely.

However, scan-tool update speed and data processing should be taken into account, so this observation should not be treated as absolute proof by itself.

3. Inspect the sensor and connector

Check for:

• Oil contamination

• Water intrusion

• Corrosion

• Bent terminals

• Loose terminals

• Damaged connector housing

• Broken locking tabs

• Harness damage

• Heat damage

The physical mounting of the sensor should also be checked.

4. Identify the sensor type

Determine whether the vehicle uses a Hall-effect, VR, or another sensor design.

This determines how the signal should be measured.

Avoid applying a generic resistance test without knowing the sensor architecture.

5. Verify power and ground

If the sensor requires external power, verify the correct supply voltage.

Check the ground circuit according to the manufacturer's procedure.

A voltage-drop test can be useful when a ground or power circuit appears normal but may have excessive resistance.

6. Test the wiring

Check the sensor circuit for:

• Open circuit

• Short to ground

• Short to voltage

• Excessive resistance

• Poor terminal contact

• Intermittent connections

Continuity testing alone may not be enough.

A wire can show continuity while still having excessive resistance or an intermittent break.

7. Check the crankshaft signal with an oscilloscope

For difficult P0335 cases, oscilloscope testing is often one of the most valuable diagnostic methods.

The waveform can reveal whether the sensor is producing:

• No signal

• Weak signal

• Distorted signal

• Missing pulses

• Irregular pulse spacing

• Electrical noise

• Intermittent dropouts

This allows the technician to observe what is actually happening rather than relying only on the fault code.

Inspect the Reluctor and Sensor Gap

If the sensor and wiring test correctly, the mechanical target needs to be considered.

Inspect the reluctor or trigger wheel for:

• Damaged teeth

• Missing or abnormal teeth

• Cracks

• Loose components

• Excessive contamination

• Incorrect positioning

Also verify the sensor installation and air gap where applicable.

A sensor can be electrically perfect but still fail to produce the expected signal if it is too far from the target or if the target itself is damaged.

Can a Bad Crankshaft Sensor Cause P0335?

Yes.

A defective crankshaft position sensor is one of the most obvious possibilities.

But the code does not prove that the sensor has failed.

For example, if the sensor has a good power supply, good ground, and produces a correct waveform at the sensor connector, replacing it would make little sense.

The problem would need to be investigated further toward the ECM, particularly the wiring and signal path.

Can Wiring Cause P0335?

Absolutely.

A wiring fault can completely interrupt the crankshaft signal.

Common examples include:

• Broken signal wire

• Corroded connector

• Short to ground

• Short to voltage

• Excessive resistance

• Loose terminal

• Damaged harness

Intermittent wiring damage can be particularly difficult because the vehicle may operate normally while stationary.

A harness that moves with engine torque can produce a fault only during acceleration or deceleration.

Can a Bad Reluctor Cause P0335?

Yes.

The crankshaft sensor cannot generate a correct signal if the target it reads is damaged or incorrectly positioned.

A reluctor problem becomes especially suspicious when:

• The sensor has already been replaced

• Wiring tests correctly

• The signal is abnormal on an oscilloscope

• The fault occurs at a particular engine speed

• Physical damage is found

Can a Timing Chain Cause P0335?

A timing-chain problem can produce crankshaft/camshaft correlation faults, but it should not automatically be blamed for P0335.

If the crankshaft sensor signal itself is missing, weak or electrically interrupted, the sensor circuit should be investigated first.

If the crankshaft signal is clean but the camshaft and crankshaft signals are incorrectly synchronized, then a timing-chain or VVT problem becomes more relevant.

Additional correlation codes can help distinguish these situations.

Can Low Battery Voltage Cause P0335?

Low battery voltage is not the direct definition of P0335.

However, battery voltage can be important during engine cranking.

If the starter causes system voltage to drop excessively, the ECM or sensor may not operate correctly.

If multiple unrelated electrical codes appear together, check:

• Battery condition

• Battery terminals

• Charging voltage

• Engine grounds

• ECM power supply

• Cranking voltage

But a healthy battery does not eliminate a crankshaft sensor circuit fault.

P0335 vs P0336, P0337, P0338 and P0339

These codes are related but provide different diagnostic information.

P0335 – Crankshaft Position Sensor “A” circuit malfunction.

P0336 – Crankshaft Position Sensor “A” circuit range/performance.

P0337 – Crankshaft Position Sensor “A” circuit low input.

P0338 – Crankshaft Position Sensor “A” circuit high input.

P0339 – Crankshaft Position Sensor “A” circuit intermittent.

The distinction is important.

P0335 is the broader circuit-malfunction code. It does not tell the technician whether the signal is specifically too high, too low, intermittent, or outside the expected performance range.

That additional information must come from testing and other diagnostic data.

What Should Be Replaced for P0335?

There is no universal part that should automatically be replaced.

If testing proves the crankshaft sensor is faulty, replace the sensor.

If the connector has poor terminal contact, repair or replace the connector.

If the wiring is damaged, repair the harness correctly.

If the sensor installation or air gap is incorrect, correct it.

If the reluctor is damaged, repair the mechanical problem.

If excessive crankshaft movement is affecting the sensor relationship, the underlying mechanical problem must be repaired.

The ECM should be considered only after the complete external circuit has been proven good.

Final Diagnostic Approach

P0335 should be treated as a general crankshaft position sensor “A” circuit malfunction, not as an automatic instruction to replace the crankshaft sensor.

A logical diagnostic path is:

Check all codes → verify whether RPM is seen during cranking → inspect the sensor and connector → identify the sensor type → verify power and ground → test the wiring → observe the actual sensor waveform → inspect the reluctor and sensor gap → compare crankshaft and camshaft signals when necessary → investigate mechanical timing if the evidence points there → consider the ECM last.

The most important point is that P0335 tells you that the ECM is not receiving or recognizing the crankshaft position signal correctly. It does not, by itself, identify the failed component.

A faulty sensor is certainly possible, but so are a broken wire, poor connector, missing power or ground, incorrect sensor gap, damaged reluctor, or an ECM input problem.