P0335 Code: Crankshaft Position Sensor Circuit Malfunction

A P0335 code means the PCM is not getting a valid signal from the crankshaft position (CKP) sensor. This is one of the most critical sensors on the engine — without it, the engine will not start. Period. The CKP tells the PCM exactly where each piston is in its stroke and how fast the engine is turning. The PCM uses this to fire the ignition coils and injectors at the right time.

If a customer rolls in with a crank-no-start and you pull P0335, do not start throwing parts. This code means circuit malfunction — the problem could be the sensor, the wiring, the reluctor wheel, or even a mechanical failure.

How the CKP Sensor Works

The CKP sensor reads a toothed reluctor wheel (tone ring) that is mounted on the crankshaft or flexplate/flywheel. The reluctor has a specific number of teeth with one or more missing teeth that serve as a reference point. The PCM counts the teeth to track RPM and identifies the missing-tooth gap to determine crankshaft position.

Hall Effect Type (3-wire)

Produces a clean digital square wave. Needs 5V or 12V reference power, ground, and signal. This is the most common type on vehicles from roughly 2005 and newer.

Variable Reluctance Type (2-wire)

Self-generating. Produces an AC sine wave signal. The voltage output increases with RPM — at cranking speed, it may only produce 0.2-0.5V AC. At idle, 1-3V AC. At higher RPM, 5V or more AC. Common on older vehicles and many Asian applications.

Common Causes of P0335

Sensor Failure

Internal failure of the sensor element. Heat is the biggest killer — the CKP sensor sits near the crankshaft, right next to the block, exposed to high temperatures. Over time, thermal cycling breaks down the internal components. Common failure on Nissan, Hyundai, and Kia applications.

Wiring and Connector Problems

The CKP sensor harness runs through a harsh environment — near the engine block, transmission bellhousing, or behind the harmonic balancer. Wires get chafed against metal edges, connectors corrode from exposure to road spray, and oil leaks can saturate connectors. Check for heat damage where the harness passes near exhaust components.

Damaged Reluctor Wheel

A cracked or chipped reluctor wheel sends an irregular signal pattern. The PCM sees the irregular pattern and flags P0335. On vehicles where the reluctor is on the flexplate, flexplate cracks can affect the signal. If the reluctor is pressed onto the crank, it can slip — rare but it happens.

Excessive Sensor Air Gap

The gap between the sensor tip and the reluctor teeth is critical. Too wide, and the signal is too weak (especially at cranking speed). Most CKP sensors have a spec gap of 0.5-1.5mm. If someone reinstalled the sensor without checking the gap, or if the sensor mounting surface has debris on it, the gap may be too large.

Harmonic Balancer Issues

On engines where the reluctor ring is bonded to the harmonic balancer (common on many GM V8s and some Ford engines), the outer ring of the balancer can slip or separate from the hub. This changes the reluctor position and corrupts the signal. Look for the outer ring being visibly offset or wobbling.

Step-by-Step Diagnosis

Step 1: Verify the Code and Check for Companion Codes

Look for related codes:

• P0340 (CMP sensor): If both CKP and CMP are setting codes, think about shared wiring, a common power/ground issue, or a timing chain problem.
• P0336 (CKP range/performance): This points more toward a reluctor issue or intermittent signal rather than a complete loss of signal.
• P0016-P0019 (cam/crank correlation): Timing chain stretched or jumped — mechanical problem, not sensor.

Step 2: Confirm Signal Presence

The fastest check: connect your scan tool and look at RPM while cranking. If the scan tool shows 0 RPM during cranking, the PCM is not receiving a CKP signal. If it shows RPM (usually 150-300 RPM during cranking), the signal is present at least intermittently and the code may be from a different condition.

Step 3: Check Power and Ground at the Connector

Unplug the CKP sensor. Key on, engine off:

• Hall effect (3-wire): Check for 5V (or 12V) reference on the power wire. Check for good ground (less than 0.1V drop) on the ground wire. If the reference is missing, check the PCM connector and the 5V reference circuit — other sensors may share it.
• VR sensor (2-wire): Measure resistance across the sensor terminals. Typical range is 200-2,000 ohms — compare to spec. OL (open) or near 0 ohms (shorted) means the sensor is bad.

Step 4: Scope the Signal

Back-probe the signal wire and crank the engine. This is the gold standard test:

• Hall effect: Look for a clean, consistent square wave. Each pulse should be the same height (0-5V). Look for the missing-tooth reference gap in the pattern — it should be a wider space between pulses. Any dropouts, glitches, or noise spikes indicate a sensor or wiring issue.
• VR sensor: Look for a clean sine wave with consistent amplitude. Each tooth should produce the same peak voltage. The missing-tooth gap will show as two wider peaks with a gap between. Look for uneven peaks (damaged reluctor teeth), low amplitude (excessive air gap or weak sensor), or noise (wiring issues).

Step 5: Inspect the Reluctor

If the sensor tests good and wiring is clean, look at the reluctor wheel. Remove the sensor and look into the bore with a light or borescope. Rotate the engine by hand and inspect every tooth. Look for chips, cracks, or debris stuck between teeth. On engines with the reluctor on the harmonic balancer, visually check for balancer separation (outer ring wobble or offset).

Step 6: Check for Intermittent Issues

P0335 can be intermittent — the engine starts fine when cold but stalls and will not restart when hot. This is classic CKP sensor heat failure. The sensor works when cool but loses its signal as it heats up from engine heat. If the code is intermittent, try to reproduce it by running the engine to full operating temperature and monitoring the CKP signal on a scope.

Common Mistakes

• Replacing the sensor without checking the reluctor. A new sensor reading a damaged tone ring is going to set the same code.
• Not checking the harmonic balancer. On GM LS engines, Chevy 3.8L V6s, and many Ford applications, a separated balancer is a common cause that gets missed.
• Ignoring the air gap. After installing a new sensor, verify the gap is within spec. Some sensors have a paper spacer on the tip that sets the gap automatically — make sure you do not remove it before installation (it wears off during engine operation).
• Not testing for intermittent heat failure. If the customer says it dies after driving 20 minutes and will not restart for 30 minutes, that is a textbook heat-soak CKP failure. Test it hot, not just cold.

Confirming the Fix

After repair, clear codes and verify CKP signal on your scan tool (RPM reads during cranking and running). Drive through a complete warm-up and cool-down cycle. Verify no codes return. If the original complaint was a no-start, verify multiple hot restarts — do not just start it once cold and call it good.

For more on sensor testing and scope diagnostics, check out the APEX Tech Nation Academy engine performance and electrical courses.