P0340
Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor)
Published · Reviewed and updated
In plain English: The engine computer did not receive a valid changing signal from camshaft position sensor A; the code identifies the sensor circuit and signal path, not automatically a failed sensor.
A vehicle may still run using a backup strategy, but drive only a short distance if starting, idle and power are normal. Stop and arrange a tow for stalling, a no-start, severe misfiring, unusual timing-chain noise or an oil-pressure warning. An intermittent cam signal can disappear without warning.
A diagnostic starting point: Failed camshaft position sensor. Start by asking: Are cranking voltage, starter speed and scan-tool engine RPM normal? Illustrative parts budgets span $0–$2500 USD, with diagnosis, labor and taxes extra.
Quick answers about P0340
- What does P0340 mean?
- The engine computer did not receive a valid changing signal from camshaft position sensor A; the code identifies the sensor circuit and signal path, not automatically a failed sensor.
- What should I check first for P0340?
- One starting point is Failed camshaft position sensor. Internal electronics can fail permanently or only when hot, but the output should be tested before replacement. The code alone does not identify a failed part; follow the procedure for your vehicle.
- Can I drive with P0340?
- A vehicle may still run using a backup strategy, but drive only a short distance if starting, idle and power are normal. Stop and arrange a tow for stalling, a no-start, severe misfiring, unusual timing-chain noise or an oil-pressure warning. An intermittent cam signal can disappear without warning.
- How much does it cost to fix P0340?
- Illustrative parts budgets in this guide span $0–$2500 USD. Diagnosis, labor and taxes are extra. P0340 can be a corroded terminal, a failed sensor or a mechanical timing job. Testing the waveform at both ends separates those very different costs.
- How do I diagnose P0340?
- Start with: Are cranking voltage, starter speed and scan-tool engine RPM normal? Begin with a stable electrical and crank-signal baseline. Low voltage, slow cranking or a missing crank signal can prevent synchronization and make the cam data misleading.
Watch the P0340 videos
Full walkthrough — 9:07. Watch on YouTube
What P0340 actually means
A trigger wheel rotates with the camshaft at half crankshaft speed. Camshaft position sensor A changes its output as the target passes. The engine computer compares that signal with the crankshaft signal to identify the compression stroke, sequence injection and monitor valve timing. If the expected cam signal never changes or does not reach the computer, it can store P0340.
P0340 sets when the controller expects activity from the primary Bank 1 camshaft-position circuit but sees no valid switching, an electrically invalid signal or no usable signal for the required engine revolutions. Exact thresholds vary by vehicle, so P0340 cannot by itself distinguish a failed sensor from its power, ground, wiring, connector, target wheel or timing relationship.
Symptoms
- Long crank or an engine that cranks but will not startSome controllers need the cam signal to identify cylinder phase quickly or to start at all.
- Intermittent stall followed by a difficult restartHeat, vibration or connector movement can interrupt a marginal sensor circuit.
- Rough running, misfires or reduced powerThe controller may substitute a backup strategy when cam synchronization is unreliable.
- Check-engine light with P0341, P0342, P0343 or P0016Companion codes help separate a dead electrical circuit from an implausible pattern or timing relationship.
- Sometimes no symptom beyond the warning lightAn intermittent dropout may be stored even though the signal is normal during the next test.
Possible causes and what to check
This is a practical diagnostic order, not measured failure rates. Follow the tests and priorities specified for your vehicle; a code alone does not identify a failed part.
The fast clue: cam/crank synchronization while cranking
Illustrative graph, not a recording from your vehicle or a universal service limit. Confirm the test conditions, units and acceptance criteria in the applicable service procedure.
Support the battery, connect a scan tool and graph engine RPM together with cam or cam-crank synchronization while cranking. Parameter names vary, and some basic readers do not expose this data.
A known-good system shows cranking RPM and changes to synchronized after the controller recognizes the cam pattern. That proves a usable signal reaches the controller at this moment.
If crank RPM is present but cam synchronization stays at no, focus on the cam circuit, its target and the cam-to-crank relationship. If engine RPM is also zero, diagnose the crank signal or starting condition first.
Synchronization is a screening clue, not a parts verdict. A scope waveform checked first at the sensor and then at the computer shows whether the signal is missing, distorted or lost in the harness.
How to diagnose it, in order
-
Are cranking voltage, starter speed and scan-tool engine RPM normal?Begin with a stable electrical and crank-signal baseline. Low voltage, slow cranking or a missing crank signal can prevent synchronization and make the cam data misleading.Yes → go to step 2No → Repair the battery, starter, ground or crank-signal condition first
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Do cam-sensor power, ground and circuit-bias checks match specification?Confirm the exact sensor pinout before probing it. Load-test suspect power and ground circuits and inspect for oil, corrosion, spread terminals and harness rub-through.Yes → go to step 3No → Repair the supply, ground, connector or shared reference circuit
-
Is the specified changing CMP waveform present at the sensor?Scope the signal while cranking or running and compare switching voltage and pattern with service information. A resistance check alone cannot prove a powered Hall sensor works dynamically.Yes → go to step 5No → go to step 4
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Are sensor mounting, air gap, target wheel and mechanical timing correct?Check for a loose or incorrectly seated sensor, debris, impact damage, a shifted target and timing-chain or cam-phaser faults. Access may require a borescope or cover removal.Yes → Replace the signal-tested failed camshaft position sensorNo → Correct the mounting, target, timing or VVT fault
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Does the same clean CMP waveform arrive at the PCM connector?Compare the signal at both ends under the same conditions while moving the harness carefully. If it reaches the PCM, verify cam-crank relationship and application-specific software before suspecting the module.Yes → Check correlation, service bulletins and the PCM input as the final branchNo → Repair the open, short or high resistance in the signal wire
Follow the cam signal from its electrical supply and rotating target to the computer; the point where it fails determines the repair.
What you need to do this yourself
- A scan tool that reads live data — Choose vehicle-compatible access to the live data, freeze frame and monitor results required by the diagnostic procedure. Some checks also need bidirectional control.
- Digital multimeter — Use the specified meter and test method for electrical checks. Follow circuit diagrams and avoid applying an unsuitable test load to a computer driver.
- Vehicle-specific service information — Confirm the procedure, safety precautions, tools and acceptance limits for the exact year, model and engine.
Some links may be affiliate links. They cost you nothing extra and do not change which tools are recommended — the diagnostic order on this site is the same either way.
Illustrative repair budgets
These are rough US planning examples, not quotes or measured repair averages. Parts and labor are separate; diagnosis, taxes, difficult access and additional repairs can increase the total.
| Repair | Parts (USD) | Labor time |
|---|---|---|
| Connector or accessible wiring repair Cost depends on whether the fault is at an exposed plug or inside a buried harness. |
$10–$300 | 1.5 h |
| Camshaft position sensor Some sensors are exposed; others require intake or cover removal. |
$25–$250 | 0.8 h |
| Sensor mounting, air-gap or trigger-wheel correction Internal targets can turn a small part problem into substantial disassembly. |
$20–$600 | 2.5 h |
| Timing chain, cam phaser or VVT repair This branch needs waveform or mechanical evidence; P0340 alone does not prove it. |
$150–$2500 | 8.0 h |
| PCM calibration, input repair or module The rare final branch after the correct waveform is verified at the PCM pins. |
$0–$1500 | 1.5 h |
P0340 can be a corroded terminal, a failed sensor or a mechanical timing job. Testing the waveform at both ends separates those very different costs.
P0340 video summary · 1:07
A brief introduction to the code and a diagnostic starting point. Use the full guide and vehicle-specific service information for the complete procedure.
Written diagnostic walkthrough
Current written guidance organized by topic. This text may include corrections made after a video was published and is not a verbatim transcript of the archived video.
Meaning and driving guidance
Code P0340. Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor).
In plain English: the engine computer did not receive a valid changing signal from camshaft position sensor A; the code identifies the sensor circuit and signal path, not automatically a failed sensor.
A vehicle may still run using a backup strategy, but drive only a short distance if starting, idle and power are normal. Stop and arrange a tow for stalling, a no-start, severe misfiring, unusual timing-chain noise or an oil-pressure warning. An intermittent cam signal can disappear without warning.
How it is measured
Here's what your engine computer is actually measuring.
A trigger wheel rotates with the camshaft at half crankshaft speed. Camshaft position sensor A changes its output as the target passes. The engine computer compares that signal with the crankshaft signal to identify the compression stroke, sequence injection and monitor valve timing. If the expected cam signal never changes or does not reach the computer, it can store P0340.
P0340 sets when the controller expects activity from the primary Bank 1 camshaft-position circuit but sees no valid switching, an electrically invalid signal or no usable signal for the required engine revolutions. Exact thresholds vary by vehicle, so P0340 cannot by itself distinguish a failed sensor from its power, ground, wiring, connector, target wheel or timing relationship.
So the code is not a part failure report. It's a performance measurement that came back under spec.
Symptoms
What you'll usually notice, beyond the light itself.
Long crank or an engine that cranks but will not start. Some controllers need the cam signal to identify cylinder phase quickly or to start at all.
Intermittent stall followed by a difficult restart. Heat, vibration or connector movement can interrupt a marginal sensor circuit.
Rough running, misfires or reduced power. The controller may substitute a backup strategy when cam synchronization is unreliable.
Check-engine light with P0341, P0342, P0343 or P0016. Companion codes help separate a dead electrical circuit from an implausible pattern or timing relationship.
Sometimes no symptom beyond the warning light. An intermittent dropout may be stored even though the signal is normal during the next test.
Possible causes
Here is a practical order for checking the possible causes. These are diagnostic priorities, not measured failure rates.
Check 1: Failed camshaft position sensor. Internal electronics can fail permanently or only when hot, but the output should be tested before replacement.
Check 2: Chafed wiring, corrosion or a loose connector terminal. Oil, water, heat and engine movement can damage the signal path or create an intermittent connection.
Check 3: Missing sensor power, ground or circuit bias. Most Hall-effect sensors require a stable supply and ground; use the factory pinout and voltage specification.
Check 4: Incorrect air gap, loose mounting or damaged trigger wheel. A healthy sensor cannot switch correctly if it is too far from the target or the target is damaged.
Check 5: Mechanical timing, VVT or oil-control problem. A stretched or jumped chain and a cam phaser fault can make the cam signal implausible relative to the crank.
Check 6: Control-module calibration or PCM input fault. This is the final branch after the correct signal has been proven at the controller pins.
Use the test results to choose the repair. A position in this list does not prove that a part has failed.
Illustrative diagnostic pattern
This illustrative graph explains a diagnostic pattern. Use the vehicle-specific procedure to interpret it.
Support the battery, connect a scan tool and graph engine RPM together with cam or cam-crank synchronization while cranking. Parameter names vary, and some basic readers do not expose this data.
A known-good system shows cranking RPM and changes to synchronized after the controller recognizes the cam pattern. That proves a usable signal reaches the controller at this moment.
If crank RPM is present but cam synchronization stays at no, focus on the cam circuit, its target and the cam-to-crank relationship. If engine RPM is also zero, diagnose the crank signal or starting condition first.
Synchronization is a screening clue, not a parts verdict. A scope waveform checked first at the sensor and then at the computer shows whether the signal is missing, distorted or lost in the harness.
Diagnostic steps
So here is the order to actually test this, cheapest and most likely first.
Step 1. Are cranking voltage, starter speed and scan-tool engine RPM normal? Begin with a stable electrical and crank-signal baseline. Low voltage, slow cranking or a missing crank signal can prevent synchronization and make the cam data misleading.
Step 2. Do cam-sensor power, ground and circuit-bias checks match specification? Confirm the exact sensor pinout before probing it. Load-test suspect power and ground circuits and inspect for oil, corrosion, spread terminals and harness rub-through.
Step 3. Is the specified changing CMP waveform present at the sensor? Scope the signal while cranking or running and compare switching voltage and pattern with service information. A resistance check alone cannot prove a powered Hall sensor works dynamically.
Step 4. Are sensor mounting, air gap, target wheel and mechanical timing correct? Check for a loose or incorrectly seated sensor, debris, impact damage, a shifted target and timing-chain or cam-phaser faults. Access may require a borescope or cover removal.
Step 5. Does the same clean CMP waveform arrive at the PCM connector? Compare the signal at both ends under the same conditions while moving the harness carefully. If it reaches the PCM, verify cam-crank relationship and application-specific software before suspecting the module.
Follow the cam signal from its electrical supply and rotating target to the computer; the point where it fails determines the repair.
Illustrative repair budgets
These are illustrative US parts budgets with labor shown separately. Diagnosis, taxes, access and additional repairs can change the total.
Connector or accessible wiring repair: 10 to 300 dollars in parts, plus about 1.5 hours of labor. Cost depends on whether the fault is at an exposed plug or inside a buried harness.
Camshaft position sensor: 25 to 250 dollars in parts, plus about 0.8 hours of labor. Some sensors are exposed; others require intake or cover removal.
Sensor mounting, air-gap or trigger-wheel correction: 20 to 600 dollars in parts, plus about 2.5 hours of labor. Internal targets can turn a small part problem into substantial disassembly.
Timing chain, cam phaser or VVT repair: 150 to 2500 dollars in parts, plus about 8.0 hours of labor. This branch needs waveform or mechanical evidence; P0340 alone does not prove it.
PCM calibration, input repair or module: 0 to 1500 dollars in parts, plus about 1.5 hours of labor. The rare final branch after the correct waveform is verified at the PCM pins.
P0340 can be a corroded terminal, a failed sensor or a mechanical timing job. Testing the waveform at both ends separates those very different costs.
Sources and application limits
This legacy guide has not yet had a page-specific source list added. Check the factory service information for your exact year, make, model and engine before acting on a test or specification.