OBD-II Diagnostic Trouble Code
P0338 — Crankshaft Position Sensor A Circuit High
P0338 means the ECM sees the crankshaft position sensor A signal voltage above the expected range, usually from an open signal or ground circuit, or a short to voltage. The ECM cannot read engine speed and position correctly.
Severity 5/5
Truck-relevant
Stop now
Severity
Stop now — do not drive
Crankshaft Position Sensor A Circuit High
Code
P0338
Category
Powertrain
Subsystem
Ignition
Truck-relevant
Yes
What this means for truckers
P0338 (Crankshaft Position Sensor A High) — CKP open or shorted to power.
Before you replace parts — try this first
P0338 on the Ignition system is most often open sensor ground or signal wire, or a loose connector pin — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Crank-no-start, stalling, or rough running on a camshaft backup signal with reduced power. The tachometer may be erratic or dead. The fault may come and go with temperature or harness movement.
Common causes
- CommonOpen sensor ground or signal wire, or a loose connector pin ($80–$400)
- CommonFailed crankshaft position sensor ($150–$500)
- OccasionalSignal wire shorted to a voltage source ($100–$500)
- RareECM input fault ($1200–$3500)
How to fix
Check the sensor ground and signal circuits for continuity and the connector for spread or backed-out pins
When to use: First step
Check the signal wire for voltage with the sensor unplugged to find a short to power
When to use: When the signal reads high with the sensor disconnected
Replace the crankshaft position sensor
When to use: When the wiring tests good
Test the ECM input per OEM procedure
When to use: Only after the sensor and wiring are confirmed good
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0300 — Random/Multiple Cylinder Misfire Detected
- → P0301 — Cylinder 1 Misfire Detected
- → P0302 — Cylinder 2 Misfire Detected
- → P0303 — Cylinder 3 Misfire Detected
- → P0304 — Cylinder 4 Misfire Detected
Frequently Asked Questions
Can I drive with code P0338?
No — P0338 is severity 5. Stop and tow if you're not near a service location. Continuing to drive can cause catastrophic engine damage. The cost of a tow ($300–800) is small compared to the cost of an engine rebuild ($15,000+).
How much does it cost to fix P0338 on a commercial truck?
Total repair cost ranges $80–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Open sensor ground or signal wire, or a loose connector pin — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0338 fail a DOT inspection?
P0338 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0338 and related codes?
P0338 is closely related to: P0300 (Random/Multiple Cylinder Misfire Detected), P0301 (Cylinder 1 Misfire Detected), P0302 (Cylinder 2 Misfire Detected), P0303 (Cylinder 3 Misfire Detected). These codes share the same subsystem (ignition) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0338 is set without the companions, the issue is more isolated.
How do I prevent P0338 from coming back after a repair?
For P0338 (Crankshaft Position Sensor A Circuit High), prevention centers on the ignition system. Use OEM-spec injectors and spark plugs (gas). Address fuel quality issues immediately — bad fuel kills injectors. Cylinder balance test annually for early warning.