P0340 means the Altima ECM lost or rejected the Bank 1 cam-position signal; it does not prove the sensor itself. Confirm engine and connector, inspect harness routing, load-test power, ground and signal, then scope cam against crank. Missing or noisy edges support a sensor, connector or wiring fault. Clean signals with a stable phase error plus P0011 or timing noise point toward the valve-timing system, chain or reluctor rather than repeated sensor replacement.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Check RPM and cam sync.
What can set P0340—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Cam sensor failure | Power/ground good; waveform absent | Signal test |
| Connector/reference/ground fault | Loaded circuit fails | Voltage-drop test |
| Harness chafe | Multiple codes/contact damage | Routing inspection |
| Cam/crank correlation fault | P0016/sync error/noise | Correlation/timing |
| Reluctor or PCM issue | Circuit passes; waveform abnormal | Scope/reluctor inspection |
Verify which signal the ECM rejected
Use the VIN-correct ESM connector view because engine families and harness routing changed across Altima generations. Read all codes for crank-sensor or shared-supply clues before disconnecting parts.
Inspect terminals for oil, corrosion and lost tension, especially near prior valve-cover or timing work. A connector that appears latched can still have a backed-out terminal.
Loaded electrical tests beat static continuity
Verify power and ground while the circuit carries an appropriate load and scope the signal during cranking. A nearly broken wire can pass meter current yet lose waveform amplitude with heat or vibration.
If several sensors share power or ground and fail together, isolate branches systematically. Replacing every sensor leaves a common wiring fault untouched.
Waveform shape chooses electrical or mechanical work
Intermittent missing edges or noise favor sensor, connector, air-gap or harness causes. Recreate the temperature and engine movement associated with the original event.
A repeatable offset between clean cam and crank patterns favors phaser, chain indexing or reluctor position. That measured relationship—not the code name—justifies opening the timing system.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Exact VIN, platform, model year and engine sales code
- All confirmed, pending and permanent companion codes
- RPM, load, coolant temperature and vehicle speed
- Relevant commanded and actual scan data
- Recent service, repairs and symptom conditions
- Manufacturer bulletin and current software/VIN status
A practical diagnostic workflow
- 01Identify sensor and engine
Cam layouts differ.
- 02Read all codes
Shared faults change priority.
- 03Inspect harness routing
Look for heat/chafe/contact.
- 04Load-test circuits
Continuity alone can mislead.
- 05Scope cam and crank
Separate dropout from phase shift.
- 06Verify hot and cold
Confirm sync and no pending code.
Do not replace the most commonly named component from P0340 alone. Confirm the exact engine, preserve evidence and complete the manufacturer test sequence before ordering parts.
Why the model year changes the test
Altima diagnostics span L31, L32, L33 and L34 generations with QR25DE, PR25DD, VQ35DE, KR20DDET and other market-specific engines, plus several conventional-automatic and CVT designs. Airflow learning, catalyst banks, valve timing, EVAP access and P1778 service strategy change across those boundaries. Confirm VIN, model year, engine, transmission code, current ECM/TCM part numbers and software before using a bulletin or diagram.
- QR/PR/KR inline-four and VQ35DE sensor layouts differ.
- Some Nissan cam and crank sensors may be physically similar; identify connectors before swapping.
- P0011/P0016 companions raise mechanical or oil-control priority.
- Repeated stalling or no-start makes diagnosis urgent.
P0340 FAQ
Is P0340 always the sensor?+
No.
Can I drive?+
Limit driving due to stall/no-start risk.
Can P0016 relate?+
Yes.
Why check other codes?+
They can reveal a shared circuit.
Can heat matter?+
Yes.
Why scope the signal?+
It separates circuit loss from timing shift.
Can a reluctor cause it?+
Yes.
What confirms repair?+
Stable cam/crank sync and no pending P0340.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01Mopar vehicle informationOfficial owner manuals and model-year engine, oil, warning and operating information↗02Stellantis/Mopar service informationFactory VIN-, platform-, engine-sales-code and calibration-specific service information↗