Crankshaft Position Sensor P0335 Code: Step-by-Step Diagnosis and Replacement Guide

Your check engine light just came on, and your scan tool reads P0335 "Crankshaft Position Sensor A Circuit Malfunction." Maybe your engine is cranking but won't start. Maybe it stalls at random. Either way, you need to figure out what's wrong before it leaves you stranded or causes expensive engine damage. Diagnosing this code the right way saves you from replacing parts that aren't broken and gets your car running again faster. This guide walks you through exactly how to diagnose a P0335 crankshaft position sensor code, step by step, so you can fix the real problem instead of guessing.

What Does the P0335 Code Actually Mean?

P0335 is a generic OBD-II trouble code that tells you the engine control module (ECM) has detected a problem with the crankshaft position sensor circuit. The "A" in the code description refers to the primary crank sensor, not a second sensor some engines use. This sensor monitors the position and rotational speed of the crankshaft, and that data is essential for fuel injection timing, ignition timing, and misfire detection.

When the ECM can't read the signal from the crankshaft position sensor or the signal is erratic, missing, or out of range it sets P0335. Without this signal, most engines won't start at all, or they'll run poorly and stall.

What Are the Common Symptoms of a P0335 Code?

Before you start testing, it helps to know what you're dealing with. P0335 usually shows up with one or more of these symptoms:

Engine cranks but won't start the most common symptom, since the ECM needs the crank signal to fire the injectors and ignition coils.
Engine stalling while driving the signal drops out intermittently, and the ECM loses timing reference.
Rough idle or misfires an unstable signal can cause erratic timing decisions.
Check engine light illuminated with or without drivability issues.
Hard starting or long cranking time the engine eventually starts but takes longer than normal.

Some of these overlap with other codes and sensor failures, which is exactly why testing matters before you replace anything.

What Causes a P0335 Code?

The code doesn't automatically mean the sensor is bad. Here's what commonly triggers it:

Failed crankshaft position sensor internal circuit failure from heat, age, or vibration.
Damaged wiring or connectors chafed wires, corroded pins, or broken connectors near the sensor.
Reluctor ring (tone ring) damage cracked, missing, or worn teeth on the crankshaft reluctor wheel.
Poor ground connection a weak or corroded ground can disrupt the sensor signal.
Timing chain or belt issues if the crank and cam are out of sync, the ECM may flag the crank sensor circuit.
ECM failure rare, but possible if everything else tests good.

On GM vehicles with the 5.3 Vortec engine, for example, crank sensor wiring problems are a well-known issue. If you're working on one of those, this guide on fixing engine speed signal problems on the GM 5.3 Vortec covers model-specific details that apply directly.

What Tools Do You Need to Diagnose P0335?

Gather these before you start. Having everything ready keeps the diagnosis moving and prevents you from cutting corners.

OBD-II scan tool one that reads live data and freeze frame, not just codes.
Digital multimeter (DMM) for testing resistance, voltage, and continuity.
Back-probe pins or test leads to check the sensor connector without damaging it.
Wiring diagram for your specific vehicle the pinout and wire colors vary by make and model.
Basic hand tools sockets, ratchets, and trim tools to access the sensor.
Oscilloscope (optional but helpful) to see the actual waveform from the sensor.

How Do You Diagnose P0335 Step by Step?

Follow these steps in order. Skipping ahead and replacing the sensor first is the single biggest mistake people make with this code.

Step 1: Scan for All Codes and Record Freeze Frame Data

Connect your scan tool and read every stored, pending, and history code. Write them all down. P0335 often appears alongside P0336 (crankshaft position sensor range/performance), P0340 (camshaft position sensor), or misfire codes. Freeze frame data shows you the engine conditions RPM, load, temperature, speed when the fault happened. That context helps you figure out if the problem is intermittent or constant.

If you also see camshaft position sensor codes, that's a strong hint the issue might be a timing chain problem or a shared wiring fault between the two sensors.

Step 2: Visually Inspect the Sensor and Wiring

Locate the crankshaft position sensor. On most engines, it's mounted near the crankshaft pulley, the flywheel/flexplate, or the engine block. Check these things with your eyes first:

Is the sensor connector plugged in tight?
Are there broken locking tabs or pushed-out pins?
Do you see oil contamination on or around the sensor? (Oil can wick into the connector and cause signal problems.)
Is the wiring harness rubbing against anything exhaust components, brackets, sharp edges?
Are there visible cracks, melted sections, or exposed copper on the wires?

A visual check takes two minutes and catches a surprising number of problems. Don't skip it.

Step 3: Check for Technical Service Bulletins (TSBs)

Before you start testing individual circuits, search for TSBs related to P0335 on your specific year, make, and model. Manufacturers sometimes issue bulletins for known wiring harness routing problems, sensor design updates, or ECM reflash procedures. A TSB can save you hours of diagnostic work.

You can search for TSBs through the NHTSA recall and complaints database or your vehicle manufacturer's service information.

Step 4: Test the Sensor's Resistance

Unplug the crankshaft position sensor connector. Set your multimeter to measure resistance (ohms). Place the probes on the sensor's signal and ground terminals. Compare your reading to the manufacturer's specification.

For most magnetic (variable reluctance) crank sensors, you'll see a resistance reading somewhere between 200 and 1,500 ohms, depending on the vehicle. Hall-effect sensors use different specs and testing methods your service manual will tell you which type you have.

If resistance is out of spec or reads open (OL): the sensor is likely bad. Replace it.
If resistance is within spec: the sensor might still be fine, but keep testing it could have an intermittent internal failure that only shows up under operating conditions.

For a detailed breakdown of wiring harness resistance testing, this wiring harness resistance test procedure walks through the process for common applications.

Step 5: Test the Wiring Between the Sensor and the ECM

This is where many diagnoses fall apart. A good sensor connected by bad wiring will still set P0335.

With the sensor unplugged and the ignition off, check each wire in the harness between the sensor connector and the ECM connector:

Continuity test: Probe both ends of each wire. You should see near-zero ohms (under 5 ohms). Anything higher means a break, high-resistance splice, or corrosion somewhere in the wire.
Short-to-ground test: Probe each wire to a known good ground. You should see no continuity (OL). If you get a reading, that wire is shorted to ground somewhere.
Short-to-power test: Probe each wire to battery positive. Again, you should see no continuity. A reading here means a short to power.

Check the ground wire separately at the sensor connector. Measure resistance from the sensor ground pin to the battery negative terminal. It should be under 1 ohm. Anything higher points to a corroded or broken ground path.

Step 6: Check the Reference Voltage and Signal Voltage

Reconnect the sensor. With the ignition on (engine off), back-probe the sensor connector to check for the reference voltage the ECM sends to the sensor. This is typically 5 volts on Hall-effect sensors. If you don't see the expected reference voltage at the connector, the problem is on the ECM side a wiring issue or a failing ECM.

If you have access to an oscilloscope, crank the engine and watch the sensor's output signal. A healthy crank sensor produces a clean, consistent waveform with evenly spaced pulses. Irregular, missing, or distorted pulses confirm a sensor or reluctor ring problem.

Step 7: Inspect the Reluctor Ring

If the sensor and wiring both test good, the reluctor ring (also called a tone ring or trigger wheel) could be the issue. This ring has evenly spaced teeth that the sensor reads as the crankshaft turns.

A cracked or chipped reluctor creates gaps in the signal.
A wobbly reluctor (from a damaged crank or improper installation) produces an erratic pattern.
Missing teeth in the wrong spot confuse the ECM's timing calculation.

You can sometimes spot reluctor damage with a borescope through the sensor mounting hole. On some engines, you'll need to remove the oil pan, timing cover, or transmission to inspect it properly.

What Are the Most Common Mistakes When Diagnosing P0335?

These are the errors that waste time, money, and patience:

Replacing the sensor without testing the wiring first. The most expensive mistake on this list. A $20 sensor swap turns into $200 when the new sensor doesn't fix it and you have to go back and test anyway.
Ignoring related codes. P0335 alongside a cam sensor code usually means you have a different root cause than an isolated P0335.
Not checking the ground circuit. A bad ground gives you all the symptoms of a dead sensor but a new sensor won't help.
Using a cheap sensor. Low-quality aftermarket crank sensors fail fast and give erratic signals. Use OEM or a proven aftermarket brand.
Forgetting to clear codes and retest after each step. You need to confirm the fix actually worked, not just assume it did.

Should You Replace the Sensor or Keep Testing?

Replace the crankshaft position sensor only after you've confirmed it's the problem through resistance testing, waveform analysis, or by process of elimination after ruling out wiring and reluctor issues. If the sensor tests bad, or if you've ruled out every other cause, replace it with a quality part.

When you do swap the sensor, make sure the air gap between the sensor tip and the reluctor ring is correct for your application. Too wide and the signal weakens; too tight and the sensor can physically contact the ring.

For a complete sensor replacement walkthrough with torque specs and fitment notes, this crankshaft sensor replacement guide covers the full procedure.

P0335 Diagnostic Checklist

Scan and record all stored, pending, and history codes plus freeze frame data.
Visually inspect the sensor, connector, and wiring harness for damage.
Check for manufacturer TSBs related to P0335 on your vehicle.
Test sensor resistance against manufacturer specifications.
Test wiring continuity, short-to-ground, and short-to-power between the sensor and ECM.
Verify ground circuit resistance is under 1 ohm.
Check reference voltage (typically 5V) at the sensor connector with ignition on.
Use an oscilloscope to evaluate the sensor waveform during cranking if possible.
Inspect the reluctor ring for cracks, missing teeth, or wobble.
Replace the sensor only after confirming it's the root cause.
Clear all codes, road test, and rescan to verify the repair.

Quick tip: If you've replaced the sensor, fixed the wiring, and P0335 keeps coming back, have the ECM tested or reflamed before you keep throwing parts at it. ECM failures are rare, but they do happen especially on high-mileage vehicles or those with a history of electrical problems.