A P0335 trouble code on a Subaru Forester means the engine control unit (ECU) has lost the signal from the crankshaft position sensor (CKP sensor): and without this signal, the ECU cannot determine where the crankshaft is in its rotation, which means it cannot time fuel injection or ignition spark, resulting in a no-start or stall condition.
This is one of the most definitive no-start codes because the CKP sensor is not optional: every modern engine requires crankshaft position data to run.
“P0335 on a Subaru is one of those codes where the diagnosis is usually straightforward once you know what to check. The sensor itself fails, or the wiring goes bad, or: and this is the one nobody expects: the reluctor ring on the crankshaft cracks. On high-mileage EJ engines especially, that ring check is not optional.” This guide covers the exact cause hierarchy for P0335 on Subaru Foresters, how to diagnose each cause step by step, generation-specific sensor locations, Subaru-specific failure patterns, and repair costs.
What P0335 Means on a Subaru Forester
Understanding the Code Definition
OBD-II Code P0335: Crankshaft Position Sensor “A” Circuit Malfunction The crankshaft position sensor (CKP sensor or CAS: crank angle sensor in Subaru documentation) is a magnetic or Hall-effect sensor that reads a reluctor wheel (also called a tone ring or trigger wheel) mounted on the crankshaft or flywheel. As the engine rotates, the reluctor wheel’s teeth pass the sensor face and generate a pulse pattern. The ECU reads this pattern to determine:
- Crankshaft rotational speed (RPM)
- Crankshaft position (which cylinder is approaching TDC: top dead center)
- Ignition timing reference
- Fuel injection timing reference When the ECU receives no signal, an intermittent signal, or a signal outside expected parameters, it stores P0335 and immediately loses the ability to fire injectors or spark plugs in proper sequence.
Why P0335 Causes a No-Start on a Subaru Forester
Without crankshaft position data, the Subaru ECU enters a fail-safe mode where it stops fuel injection entirely on most calibrations. The engine may crank normally (the starter motor and battery are separate from the CKP circuit) but will not fire and will not start. Some Subaru calibrations allow the engine to start briefly on the camshaft position sensor signal alone before shutting down again, resulting in a brief start that immediately stalls.
Subaru Forester Generation-Specific CKP Sensor Locations
EJ Engine Series (1998 to 2013 Forester: EJ25, EJ20)
On EJ-series Subaru Forester engines, the crankshaft position sensor is located at the rear of the engine, near the bell housing area on the passenger side of the transmission bellhousing flange. The sensor faces the flexplate (automatic transmission) or flywheel (manual transmission) reluctor ring. Access: the sensor is accessible from underneath the vehicle but requires removing the engine splash shield and may require removing an exhaust heat shield. It is not visible from above with the hood open.
FB Engine Series (2014 to Present Forester: FB25, FA20)
On FB-series Subaru Forester engines, the crankshaft position sensor is located lower on the engine block, typically on the front or driver’s side of the block, facing the crankshaft reluctor wheel that is integral to the crankshaft itself rather than on the flywheel. Access is generally from below after removing the engine splash shield. Note: the FA20 (used in the XT/turbo models) has a different sensor routing than the FB25. Always confirm the specific sensor location using a Subaru service manual or model-year-specific diagram before purchasing a replacement.
The P0335 Cause Hierarchy for Subaru Forester
Cause 1: Failed Crankshaft Position Sensor (Most Common)
The sensor itself fails electrically: the internal coil opens, the Hall-effect element fails, or the sensor body cracks from heat cycling. This is the most common cause and the first component to test.
How to Test the CKP Sensor
Resistance test (magnetic/inductive sensors: common on EJ engines): Disconnect the sensor electrical connector. Set a multimeter to the resistance (ohms) setting. Measure resistance across the two signal terminals of the sensor. Compare to the Subaru specification for your specific engine:
- EJ25 CKP sensor specification: approximately 1,630 to 2,370 ohms at 20°C (68°F)
- A reading of infinite resistance (open circuit) or near-zero resistance (short) indicates a failed sensor Voltage output test (Hall-effect sensors: common on FB engines): With the sensor connected and the engine cranking, use a multimeter on the AC voltage setting or a scan tool with live data to observe whether the sensor is producing a signal during cranking. No signal during cranking with voltage and ground confirmed at the connector indicates a failed sensor.
CKP Sensor Replacement Cost
Sensor part: $30 to $90 for OEM-spec replacement. Genuine Subaru (Denso-sourced): $60 to $120. Aftermarket options are available but quality varies significantly: use a reputable brand. Labor: 1 to 2 hours at an independent shop. EJ-engine location near the bellhousing is less accessible than FB-engine locations. Total shop cost: $150 to $300 for a straightforward sensor replacement.
Cause 2: Wiring Harness Damage (CKP Circuit)
What the Wiring Circuit Consists Of
The CKP sensor on Subaru Forester models has a 2-wire (EJ inductive) or 3-wire (FB Hall-effect) connector. The wiring runs from the sensor along the engine harness to the ECU. On EJ-engine Foresters specifically, this harness segment runs along the bottom of the engine near exhaust components and is exposed to heat, moisture, and road debris.
Common Wiring Failures on Subaru Foresters
- Chafed insulation: the harness may have areas where insulation has worn through against the engine block, exhaust components, or chassis brackets, creating a short circuit or intermittent open
- Corroded connector terminals: moisture intrusion at the sensor connector corrodes the female terminals, increasing resistance or creating intermittent contact
- Broken wire inside intact insulation: wiring that has been flexed repeatedly can break internally while the insulation remains visually intact: this is called an intermittent open circuit
How to Test the Wiring
Step 1: Power and ground at the connector (FB/Hall-effect sensors): with the ignition on, backprobe the connector with a multimeter. Confirm 5V reference voltage on the reference wire and 0V (ground) on the ground wire. No voltage on the reference wire indicates a wiring problem between the connector and the ECU. Step 2: Continuity test: with both ends of the harness disconnected (sensor connector and ECU connector), test continuity along each wire. Infinite resistance anywhere in the wire indicates a break. Step 3: Wiggle test: with a scan tool monitoring live CKP sensor data (or with an assistant watching for the P0335 code to set or clear), wiggle the harness at the sensor connector, along its routing, and at the ECU connector while the engine cranks. If the signal drops or the code sets during the wiggle, the break is in that section of the harness. Wiring repair cost: $80 to $250 for a harness section repair at an independent shop. Full harness replacement if the damage is extensive: $300 to $600 including parts and labor.
Cause 3: Cracked or Damaged Reluctor Ring (Subaru-Specific Critical Check)
What the Reluctor Ring Is
The reluctor ring (tone ring, trigger wheel) is a toothed metal wheel that the CKP sensor reads as it rotates past the sensor face. On EJ-engine Subaru Foresters, this ring is pressed onto the crankshaft or integrated into the flexplate/flywheel assembly. On FB-engine Foresters, it is machined directly into the crankshaft.
Why This Is a Subaru-Specific Concern
On high-mileage EJ-series engines, the pressed-on reluctor ring can develop cracks or lose teeth from thermal cycling, corrosion, and fatigue. A cracked reluctor ring that has dropped a tooth produces a P0335 code but will not be resolved by replacing the CKP sensor: the sensor will correctly report the absence of the missing tooth as a signal error.
“We’ve had cars come in two and three times after sensor replacements at other shops still throwing P0335. When we pull the transmission and look at the flywheel ring, there it is: a crack right through one of the teeth. The sensor was fine the whole time.”
How to Check the Reluctor Ring
The reluctor ring inspection requires visual access to the flywheel or flexplate. On most Subaru Foresters, this requires:
- Removing the transmission inspection cover or starter motor to gain visual access to the flywheel/flexplate area
- Rotating the engine by hand (using the crankshaft pulley bolt) and inspecting each tooth of the reluctor ring with a flashlight
- Looking for missing teeth, cracks across tooth bases, or sections of the ring that have separated On FB-engine Foresters where the reluctor is machined into the crankshaft, damage is less common but still possible from impact or severe overheating. Reluctor ring replacement cost: on EJ engines with a pressed-on ring: ring replacement requires transmission removal: $500 to $1,000 including parts and labor. Replacement is often recommended alongside a clutch service on manual transmissions to avoid repeating the transmission removal cost.
Cause 4: ECU (Engine Control Unit) Failure: Rare
A failed ECU input circuit for the CKP sensor signal produces P0335 when every other component in the circuit tests correctly. This is the last-resort diagnosis after the sensor, wiring, and reluctor ring have all been confirmed as functional.
How to Confirm ECU Involvement
An ECU fault in the CKP input circuit is confirmed when:
- The CKP sensor tests within specification on the bench
- All wiring tests confirm continuity and correct voltage
- The reluctor ring is visually intact with no missing or cracked teeth
- Substituting a known-good CKP sensor does not change the code or the no-start condition ECU replacement or repair cost: a used ECU from a donor vehicle (requires VIN matching and in some cases immobilizer reprogramming): $100 to $300. Remanufactured ECU from a specialist: $250 to $600. New OEM ECU from Subaru: $800 to $1,500.
Step-by-Step P0335 Diagnosis Flowchart for Subaru Forester
| Step | Action | If Result Is Good | If Result Is Faulty |
|---|---|---|---|
| 1 | Read all stored codes; note any additional CMP (P0340) or related codes | Proceed to sensor test | Additional codes may indicate different root cause |
| 2 | Inspect CKP sensor connector for corrosion, moisture, and bent terminals | Proceed to sensor resistance test | Clean or repair connector first |
| 3 | Test CKP sensor resistance (EJ) or voltage output (FB) during cranking | Proceed to wiring test | Replace CKP sensor |
| 4 | Test wiring continuity and wiggle-test harness | Proceed to reluctor ring inspection | Repair wiring harness |
| 5 | Visually inspect reluctor ring teeth through inspection cover or with starter removed | Proceed to ECU test | Replace reluctor ring (transmission removal required) |
| 6 | Substitute known-good CKP sensor; verify signal at ECU connector | ECU input circuit confirmed faulty | Review diagnosis; retest sensor and wiring |
| 7 | If all tests pass and code remains with known-good sensor | ECU replacement or specialist ECU repair | : |
Frequently Asked Questions
What Is P0335 on a Subaru Forester?
P0335 on a Subaru Forester means the ECU has detected a malfunction in the crankshaft position sensor “A” circuit: either no signal is being received, the signal is intermittent, or the signal pattern is outside expected parameters. Without this signal, the ECU cannot determine crankshaft position and cannot time fuel injection or ignition, resulting in a no-start condition.
Can I Drive a Subaru Forester With a P0335 Code?
No. A P0335 code that causes a no-start means the vehicle cannot be driven. If the code is stored but the vehicle is currently starting and running (intermittent failure), driving should be limited to reaching a shop because the vehicle can stall at any time without warning when the intermittent failure recurs.
How Do I Fix P0335 on a Subaru Forester?
Start by inspecting the CKP sensor connector for corrosion and the wiring for damage. Test the sensor resistance or signal output per the procedure above. Replace the sensor if it fails its test. If the sensor tests correctly, inspect the reluctor ring for cracked or missing teeth before assuming the sensor is faulty. Confirm wiring continuity through the full harness before concluding ECU involvement.
How Much Does It Cost to Fix P0335 on a Subaru Forester?
Replacing the CKP sensor: $150 to $300 at an independent shop. Wiring harness repair: $80 to $250. Reluctor ring replacement (requires transmission removal): $500 to $1,000. ECU replacement or repair: $250 to $1,500. Always diagnose before replacing: replacing the sensor without checking the reluctor ring is the most common mistake and most common reason for repeat P0335 codes.
Why Does My Subaru Forester Crank But Not Start With P0335?
When the ECU cannot confirm crankshaft position from the CKP sensor, it stops fuel injection and ignition spark to prevent engine damage from a misfired injection sequence. The starter motor and battery are not involved in this logic: they continue to operate normally, which is why the engine cranks strongly but will not fire.
Is the Reluctor Ring the Same as the Flywheel Ring Gear?
No. The reluctor ring (tone ring) is a separate toothed ring that the crankshaft position sensor reads for position data. It has evenly spaced teeth except for one or two missing teeth that serve as reference points. The flywheel ring gear is a much larger ring with many more teeth that the starter motor engages to crank the engine. They are separate components with separate functions.
The Bottom Line
P0335 on a Subaru Forester is a code with a clear diagnostic path and a consistent cause hierarchy. Test the sensor first because it is the most common failure and the cheapest fix. Test the wiring second because harness damage near the exhaust is a well-documented Subaru failure point. Inspect the reluctor ring third: especially on EJ-engine models with high mileage: before concluding the sensor is bad just because the code points to the sensor circuit. The Subaru-specific pattern of reluctor ring cracking on EJ engines is the most commonly missed diagnosis in P0335 cases. A shop that replaces the CKP sensor without inspecting the reluctor ring and then returns the car still not starting has not completed the diagnosis. Insist that the ring be inspected before any repeat sensor replacements are authorized.