OBD-II Diagnostic Trouble Code
P0385 — Crankshaft Position Sensor B Circuit
P0385 means the ECM is not getting a valid signal from crankshaft position sensor B. Only some engines use a second crank sensor, often for redundancy or for a separate timing function, so where sensor B sits and how the ECM uses it differs by engine.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Crankshaft Position Sensor B Circuit
Code
P0385
Category
Powertrain
Subsystem
Ignition
Truck-relevant
Yes
What this means for truckers
P0385 (Crankshaft Position Sensor B Circuit) — some commercial diesels (Cummins X15) have two crank sensors. The secondary failed. Truck may run on the primary but lose redundancy. Replacement: $80-300 part.
Before you replace parts — try this first
P0385 on the Ignition system is most often failed crankshaft position sensor b — 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
Check-engine light, possibly longer cranking or rough running. If sensor A is working, many engines run normally on it. If both crank signals are compromised, the engine may not start or may stall.
Common causes
- CommonFailed crankshaft position sensor B ($150–$500)
- CommonDamaged wiring or connector for sensor B ($100–$500)
- OccasionalDebris on the sensor tip or a damaged tone wheel ($150–$1500)
- RareECM input fault ($1200–$3500)
How to fix
Identify sensor B with service information, then inspect its connector and harness
When to use: First step
Check supply, ground and signal and scope the output while cranking
When to use: To separate sensor from wiring faults
Remove the sensor, clean debris, inspect the target and replace the sensor
When to use: When the signal is missing or weak
Test the ECM input per OEM procedure
When to use: Only after the sensor and wiring are cleared
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 P0385?
Drive with caution. P0385 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0385 on a commercial truck?
Total repair cost ranges $100–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Failed crankshaft position sensor B — 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 P0385 fail a DOT inspection?
P0385 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 P0385 and related codes?
P0385 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 P0385 is set without the companions, the issue is more isolated.
How do I prevent P0385 from coming back after a repair?
For P0385 (Crankshaft Position Sensor B Circuit), 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.