P0338 Code: Crankshaft Position Sensor A Circuit High
The crank signal line sits at 5 or 12 volts and stops switching: open ground, open wire or short to power.
Stop driving
If the engine won't start, tow it rather than repeatedly cranking. If it runs, the fault is intermittent and can kill the engine without warning, so drive only a short, slow distance to a shop. A short to 12 volts can also damage the computer's input, so don't leave it unrepaired.
At a glance
Severity: High
- Meaning
- Crankshaft Position Sensor A Circuit High
- System
- Ignition & Misfire · Powertrain
- Safe to drive?
- With caution
- Typical repair cost
- $40–$1,500
- DIY difficulty
- Moderate
A Hall-effect crank sensor can only pull its signal line down; the engine computer's internal pull-up provides the high state. So when the sensor loses its ground, loses its supply, or the wire between sensor and computer breaks, the line simply floats up to about 5 volts and stays there. The same thing happens if the signal wire touches a powered circuit, except the reading may then be battery voltage. P0338 is set when the computer sees that line held above its upper threshold instead of toggling with the tooth pattern. The result for the engine is the same as a missing signal: no crank reference, so a no-start or a sudden stall.
How to read P0338
- P Powertrain
- 0 Generic (SAE)
- 3 Ignition / misfire
- 38 Specific fault
Symptoms
- Crank-no-start with zero rpm on the scan tool
- Engine stalls, then restarts normally a few minutes later
- Tachometer drops out at the moment of stalling
- Other codes on the same ground or reference, such as MAP or throttle position circuit high
- Problems started right after work near the sensor, a remote-start or alarm install, or engine washing
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Open or corroded sensor ground, including a loose engine-to-body ground strap
- Broken signal wire or a spread terminal in the connector, so the line floats high
- Crank sensor failed internally and no longer switches the line low
- Water or oil in the connector bridging the reference pin to the signal pin
- Signal wire shorted to a 12-volt feed, often at a poorly spliced remote-start, alarm or trailer harness
- Wrong replacement sensor (different output type or supply voltage)
- Engine computer input fault, sometimes after a 12-volt short
Diagnosis step by step
Note the exact signal voltage with the sensor connected
Back-probe the signal wire at the sensor with the connector plugged in and crank the engine. A good Hall sensor gives a rapidly changing reading averaging somewhere between 0 and 5 volts. A steady 5 volts means the sensor isn't pulling the line down; a steady 11 to 14 volts means the wire is touching a powered circuit.
Tools: Multimeter
Voltage-drop test the sensor ground
With one lead on the sensor's ground pin (back-probed) and the other on battery negative, crank the engine. More than about 0.1 volt means resistance in the ground path. Check the engine ground strap and the ground eyelets on the block or head, which are easy to leave loose after a repair.
Tools: Multimeter
Check the connector and pin tension
Unplug the sensor and look for water, coolant or oil between pins, green corrosion, and terminals that have been pushed back or spread by a test probe. A female terminal that grips a test pin loosely can open under vibration.
Tools: Flashlight, Screwdriver
Continuity-test the signal wire
Battery disconnected, computer connector unplugged, measure from the sensor connector signal pin to the matching computer pin. Expect under about 1 ohm. Wiggle the harness while measuring; an open that comes and goes with movement is a broken conductor inside intact insulation.
Tools: Multimeter
Hunt for a short to 12 volts
If you saw battery voltage on the signal wire, unplug the sensor and computer and measure from the signal wire to battery positive with the key on. Any reading means contact with a powered circuit. Look first at any aftermarket splices, then where the harness passes other powered looms.
Tools: Multimeter, Flashlight
Confirm the replacement part and verify
If the wiring is good and the sensor still holds the line high, replace it, checking the part matches the original's connector, tip length and supply voltage. Then crank while watching rpm on the scan tool and confirm the engine starts immediately, hot and cold.
Tools: OBD-II scanner
Where the parts are
- 1Ignition coil
- 2Spark plug
- 3Fuel injector
- 4Camshaft sensor
- 5Crankshaft sensor
- 6Engine computer (ECM)
- 7Intake manifold
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean and tighten engine ground strap or sensor ground | Yes | $40–$150 |
| Repair open signal wire or re-pin connector | No | $110–$380 |
| Replace crankshaft position sensor | Yes | $150–$450 |
| Remove faulty aftermarket splice and repair short to power | No | $120–$400 |
| Replace or repair engine computer after input damage | No | $500–$1,500 |
Rough US estimates for parts and labor; shop rates vary by region. Not a quote.
Emissions / smog test impact
Will fail
With P0338 stored and the check-engine light on, the vehicle fails an OBD emissions inspection. Because the fault can stop the engine, fix it before the test and let the monitors complete over a few drives.
Frequently asked questions
How can an open wire make the voltage high?
The computer supplies the high level itself through a resistor. The sensor's only job is to pull that level down at each tooth. If the wire breaks or the sensor loses its ground, nothing pulls the line down, so it sits at the pull-up voltage and the computer reads 'high'.
I see 12 volts on the signal wire. Is that bad?
Yes. The signal should never rise above about 5 volts on most engines, so battery voltage means the wire is touching a powered circuit. Find and fix the short quickly, because it can overheat the sensor or damage the computer's input stage.
Could this be caused by a remote starter or alarm?
It can. Some installations tap tachometer or crank signals, and a poor splice or a module fault can back-feed voltage onto the line. If P0338 appeared after an install, unplug that module and retest before replacing anything.
Is P0338 different from P0337 in practice?
Yes. P0337 means the line is pinned to ground, so you look for chafed wires touching metal. P0338 means it is stuck high, so you look for open grounds, broken wires, a dead sensor that no longer switches, or contact with a powered circuit.