OBD-II Diagnostic Trouble Code
P0340 — Camshaft Position Sensor A Circuit (Bank 1)
P0340 means the ECM is not getting a valid signal from camshaft position sensor A on bank 1 (on inline engines there is just one bank). The camshaft signal tells the ECM which stroke each cylinder is on for injection and ignition sequencing.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
Camshaft Position Sensor A Circuit (Bank 1)
Code
P0340
Category
Powertrain
Subsystem
Ignition
Truck-relevant
Yes
What this means for truckers
P0340 (Camshaft Position Sensor A Bank 1) — cam sensor circuit fault. Cam timing reference lost; engine may not start. Replacement: $80-300.
Before you replace parts — try this first
P0340 on the Ignition system is most often failed camshaft position sensor — 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
Longer cranking before start, or a no-start on engines that need the cam signal to sync. Once running, the engine may run normally, misfire or go into reduced power. Some diesels start only after the ECM syncs on the crank signal alone, which takes several seconds of cranking.
Common causes
- CommonFailed camshaft position sensor ($120–$450)
- CommonDamaged wiring or a corroded or loose connector at the cam sensor ($100–$450)
- OccasionalShorted or open 5-volt reference or ground circuit ($100–$600)
- RareDamaged camshaft target wheel or sensor air gap problem ($300–$2500)
- RareECM input fault ($1200–$3500)
How to fix
Inspect the cam sensor connector and harness, and check for supply, ground and signal while cranking
When to use: First step
Scope the cam signal alongside the crank signal
When to use: To confirm whether the sensor is putting out a pattern
Replace the camshaft position sensor
When to use: When supply and ground are good but there is no signal
Check for a shorted shared 5-volt reference by unplugging other sensors
When to use: When other sensor codes set at the same time
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 P0340?
Drive with caution. P0340 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 P0340 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 camshaft position sensor — 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 P0340 fail a DOT inspection?
P0340 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 P0340 and related codes?
P0340 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 P0340 is set without the companions, the issue is more isolated.
How do I prevent P0340 from coming back after a repair?
For P0340 (Camshaft Position Sensor A Circuit (Bank 1)), 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.