P0338 – Crankshaft Position Sensor “A” Circuit High

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit High | Location: Designator A

Definition source: SAE J2012/J2012DA (industry standard)

P0338 indicates the powertrain control module has detected a high electrical input on the Crankshaft Position Sensor “A” circuit. In practical terms, the module is seeing the crank sensor signal or its circuit held higher than expected, which can disrupt how it calculates engine speed and crank position for ignition and fuel control. This is an electrical condition, not proof that the sensor itself is bad. The exact monitor strategy, enabling conditions, and what the module considers “high” vary by vehicle, so always confirm connector pinouts, circuit type, and test specifications using the correct service information before repairs.

What Does P0338 Mean?

P0338 – Crankshaft Position Sensor “A” Circuit High means the control module detected that the Crankshaft Position Sensor “A” signal circuit is reporting a consistently high voltage level (high input) compared to what the module expects during self-tests or normal operation. Under SAE J2012 terminology, “circuit high” points to an electrical fault category such as a short-to-power, an open ground, a pulled-up signal, or a biased circuit that cannot switch correctly. The code identifies the circuit behavior (high input) and the monitored circuit (“A”), and it should be diagnosed with circuit testing rather than assumed component replacement.

Quick Reference

• Subsystem: Crankshaft position sensor “A” signal circuit (engine speed/position input to the powertrain control module).
• Common triggers: Signal wire shorted to a power feed, sensor ground open/high resistance, connector damage causing pull-up, incorrect reference/feed present where it should not be, or signal biased high due to harness faults.
• Likely root-cause buckets: Wiring/connector faults, power/ground distribution issues, sensor internal electrical fault, incorrect installation/connector pin fit, control module input circuit fault (less common).
• Severity: Often high—may cause no-start, stall, misfire, or reduced power because crank position is critical for engine timing.
• First checks: Verify connectors fully seated, inspect harness routing near heat/moving parts, check for shared power/ground issues, and review scan data for RPM/crank signal behavior during cranking.
• Common mistakes: Replacing the sensor before verifying shorts-to-power, ground integrity, and connector pin tension; ignoring intermittent harness faults that only appear with vibration or heat.

Theory of Operation

The crankshaft position sensor provides the control module with a repeating signal that corresponds to crankshaft speed and position. Depending on vehicle design, the sensor may be a magnetic pickup (generating an AC-like waveform) or a digital sensor that uses a supplied reference and ground to switch a signal on and off. The module uses this input to calculate engine RPM, synchronize fuel injection, and control ignition timing.

For a “circuit high” fault, the module detects the crank sensor input stuck high, biased high, or otherwise above the expected range for too long when the engine is cranking or running. This can happen if the signal wire is shorted to a voltage source, if the sensor ground is open (allowing the signal to float high), or if connector/harness damage alters the circuit’s ability to transition normally.

Symptoms

• No-start condition, especially if the module cannot determine crank position during cranking.
• Stalling or sudden engine shut-off if the signal fails while driving.
• Hard start with extended cranking time before the engine fires.
• Misfire or rough running due to incorrect timing calculations from an invalid crank input.
• Reduced power or limited performance if the module enters a fallback strategy.
• Tachometer reading erratic, stuck, or dropping to zero (varies by vehicle and network logic).
• Check engine light illuminated and possibly additional related sensor/ignition/injection codes depending on strategy.

Common Causes

• Harness damage or chafing causing a short-to-power on the crankshaft position sensor “A” signal circuit
• Open ground (broken ground wire, loose ground fastener, poor splice) driving the signal high relative to module ground
• Poor connector fit (spread terminals, corrosion, moisture intrusion) creating an unintended high signal or skewed return path
• Crossed circuits after repairs (signal wire pinned into a power or reference cavity, or harness swapped between similar connectors)
• Sensor internal fault producing an abnormally high output or failing in a way that biases the signal high
• Reference/feed circuit fault (if the design uses a supplied reference/voltage feed) that backfeeds the signal circuit high
• Aftermarket wiring changes or add-on electronics that introduce backfeed voltage into the sensor circuit
• Module or terminal issue at the control module connector (backed-out pin, corrosion, damaged terminal) causing erroneous high input detection

Diagnosis Steps

Tools that help: a scan tool that can read live data and capture logs, a digital multimeter, and (where available) an oscilloscope for signal integrity checks. You’ll also want basic back-probing leads, a wiring diagram/service information for your exact vehicle, and supplies to clean/repair terminals. Perform testing with safe access to wiring and rotating components.

1. Confirm the DTC and freeze-frame data: Scan for P0338 and record freeze-frame/extended data (engine speed, battery voltage, temperature, cranking vs running). Check for related codes (crank/cam correlation, sensor supply, power/ground) and address power supply or network codes first if present.
2. Verify the complaint and operating condition: Determine whether P0338 sets during cranking, idle, decel, or at steady RPM. If possible, reproduce the condition in a controlled setting to avoid chasing a one-time event.
3. Initial visual inspection: With ignition off, inspect the crankshaft position sensor “A” connector and harness routing. Look for rubbing, melted insulation, oil saturation, pin damage, prior repair splices, or evidence of the harness contacting a power feed. Confirm connectors are fully seated and locked.
4. Check live data plausibility (signal presence, not thresholds): On the scan tool, observe engine speed (RPM) and any crank sensor PID while cranking/running. If RPM is erratic, drops out, or shows an implausible jump when the code sets, note the exact moment and conditions. Save a data log if your tool allows it.
5. Wiggle test with logging: While monitoring the live data log (and with the engine idling if it can run safely), gently wiggle the sensor connector, nearby harness segments, and any intermediate connectors. If RPM/signal glitches or the DTC sets, isolate the section that triggers the fault and focus inspection there.
6. Connector and terminal checks: Disconnect the sensor and inspect both sides for corrosion, moisture, terminal push-out, or spread terminals. Verify terminal tension (pin fit) mechanically. Clean/repair as needed before proceeding; poor pin fit can mimic a circuit-high condition.
7. Circuit high diagnostics (key on, engine off where applicable): Using the wiring diagram, identify the signal circuit, sensor ground/return, and any reference/feed. Check for unintended voltage on the signal circuit. If the signal shows power when it should not, suspect a short-to-power or backfeed from a neighboring circuit.
8. Short-to-power isolation: If the signal circuit is high, unplug modules/sensors on the same harness branch one at a time (as service info allows) to see when the high condition disappears. This helps separate a harness short from an internal sensor or module backfeed. Recheck after each change.
9. Voltage-drop testing of grounds and returns: With the circuit loaded (cranking or running if possible and safe), perform voltage-drop tests on the sensor ground/return and the module ground paths related to this input. Excessive drop indicates high resistance or an open/weak ground that can cause the module to interpret the signal as high.
10. Signal integrity check (preferred with a scope): If available, scope the crankshaft position sensor “A” signal at the sensor connector and at the module connector. Compare for distortion, unexpected bias high, or dropouts that appear only at one end (pointing to wiring/connector issues). Avoid relying on generic wave shape/voltage “normals”; use service information and relative comparison.
11. Sensor and harness decision point: If the signal stays high with the sensor unplugged, the issue is in wiring/connector/module input (short-to-power, backfeed, terminal issue). If the signal returns to normal with the sensor unplugged and goes high only when connected, suspect the sensor or its immediate connector/terminal fit, then retest after repair or substitution per service info.
12. Post-repair verification: After correcting the verified cause, clear codes and perform a road test/drive cycle under the same conditions captured in freeze-frame. Recheck for pending codes and confirm stable RPM/signal data in the log.

Professional tip: If P0338 is intermittent, prioritize capturing a live-data log during the exact event and correlate it with a targeted wiggle test. A brief harness-to-power contact or an intermittent ground open can set a circuit-high code without leaving obvious physical damage, so combine terminal tension checks with voltage-drop testing under load rather than relying on static continuity tests alone.

Possible Fixes & Repair Costs

Repair costs for P0338 vary widely because the correct fix depends on what is driving the crankshaft position sensor “A” circuit high: wiring faults, connector issues, sensor problems, or (less commonly) a control module input concern. Labor and access also vary by vehicle.

• Repair wiring damage in the crankshaft position sensor “A” signal circuit (short-to-power, rubbed-through insulation, melted harness sections)
• Clean, reseat, or replace affected connectors/terminals (corrosion, moisture intrusion, spread pins, poor pin fit, damaged locks)
• Restore proper power/ground integrity for the sensor circuit (repair opens, high resistance, or ground faults found during voltage-drop testing)
• Replace the crankshaft position sensor “A” only after confirming the circuit and power/ground are correct and the signal remains high
• Correct routing/retention issues so the harness cannot chafe or contact hot/moving components
• Repair related circuit faults at the control module connector (pin tension, corrosion) when proven by testing
• Reprogram/replace the control module only if service information supports it and circuit testing confirms the input remains biased high with known-good wiring/sensor

Can I Still Drive With P0338?

Driving with P0338 is not recommended if the engine stalls, will not start, runs in reduced-power mode, or the tachometer/engine speed signal is erratic, because a crankshaft position input issue can cause sudden loss of power. If the vehicle seems to run normally, keep trips short, avoid high-speed driving, and schedule diagnosis promptly; stop driving immediately if stalling, misfiring, or warning indicators appear.

What Happens If You Ignore P0338?

Ignoring P0338 can lead to intermittent no-start, stalling, or unstable engine operation as the control module loses a reliable crankshaft position signal. Continued operation with an electrical high input fault may also complicate future diagnostics, trigger additional fault codes, and increase the chance of being stranded due to an unpredictable restart condition.

Related Sensor Crankshaft Codes

Compare nearby sensor crankshaft trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P0388 – Crankshaft Position Sensor “B” Circuit High
• P0393 – Camshaft Position Sensor “B” Circuit High Bank 2
• P0368 – Camshaft Position Sensor “B” Circuit High Bank 1
• P0808 – Clutch Position Sensor Circuit High
• P2963 – Intake Air Metering Control Valve Position Sensor Circuit High
• P2619 – Crankshaft Position Signal Output Circuit High

Key Takeaways

• P0338 indicates a detected high input condition in the crankshaft position sensor “A” circuit, not a confirmed mechanical failure.
• The most common root causes are short-to-power wiring faults, connector/terminal issues, or power/ground integrity problems.
• Test-driven diagnosis should focus on the sensor signal circuit and its reference/ground paths before replacing parts.
• Live-data logging and wiggle testing are effective for catching intermittent circuit-high events.
• Do not continue driving if stalling or no-start occurs; address the fault promptly to avoid being stranded.

Vehicles Commonly Affected by P0338

• Passenger cars with electronically controlled fuel injection and distributorless ignition
• Light-duty trucks and vans using a crankshaft position sensor for engine speed and timing
• Vehicles with sensor harness routing near heat sources or moving components (chafe risk varies by vehicle)
• High-mileage vehicles where connector seals and terminal tension may be degraded
• Vehicles operated in wet, salty, or dusty environments that promote connector contamination
• Vehicles with recent engine work where sensor connectors may be left loose or harnesses misrouted
• Vehicles with modified electrical systems where added wiring can introduce shorts or poor grounds
• Vehicles that have experienced prior collision or underbody damage affecting harness integrity

FAQ

Does P0338 mean the crankshaft position sensor is bad?

No. P0338 means the control module detected the crankshaft position sensor “A” circuit signal as high. That can be caused by a short-to-power, an open/failed ground path, connector/terminal problems, or a sensor fault. Confirm the circuit condition with testing before replacing the sensor.

What electrical problems most often cause a “circuit high” code like P0338?

Common causes include a signal wire shorted to a power feed, a damaged harness where insulation has rubbed through, a corroded connector that biases the input high, or an open ground/reference return that prevents the signal from being pulled to its proper range. The exact failure mode varies by vehicle design.

Can a loose connector cause P0338?

Yes. Poor pin fit, spread terminals, partial engagement, or moisture/corrosion in the connector can create an abnormal high input condition or intermittent spikes that the module interprets as circuit high. A careful connector inspection and pin-tension check is an important first step.

Will P0338 cause a no-start or stalling?

It can. If the control module cannot rely on the crankshaft position signal, it may disable fuel and/or spark timing control, which can result in extended cranking, a no-start, or sudden stalling. Some vehicles may also enter a reduced-power strategy depending on how the system is designed.

What should I check first before replacing parts for P0338?

Start with a visual inspection of the sensor harness and connector, then verify power/ground integrity and check for a short-to-power on the signal circuit. If available, log scan-tool data while performing a wiggle test to catch intermittent circuit-high events. Confirm the fault with repeatable evidence before replacing components.

After repairs, clear the code, verify normal crankshaft signal behavior on live data (varies by vehicle), and complete a road test or run procedure to confirm P0338 does not return.