P0340

00:00What this code means

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.

00:40How the test actually works

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.

01:43Symptoms

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.

02:41Most likely causes, ranked

Now the part you came for: what actually causes this, ranked by how often it turns out to be the culprit.

28 percent of the time, it's this: Failed camshaft position sensor. Internal electronics can fail permanently or only when hot, but the output should be tested before replacement.

26 percent of the time, it's this: Chafed wiring, corrosion or a loose connector terminal. Oil, water, heat and engine movement can damage the signal path or create an intermittent connection.

16 percent of the time, it's this: Missing sensor power, ground or circuit bias. Most Hall-effect sensors require a stable supply and ground; use the factory pinout and voltage specification.

11 percent of the time, it's this: 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.

11 percent of the time, it's this: 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.

8 percent of the time, it's this: Control-module calibration or PCM input fault. This is the final branch after the correct signal has been proven at the controller pins.

Notice that the most expensive repair is not the most likely one. That matters, because the cheap checks come first.

04:14The measurement that decides it

This is the single measurement that tells you whether you need the expensive part or the cheap one.

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.

05:13Diagnostic order

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.

07:01Repair costs

What this costs to put right, in US dollars, parts and labor.

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.

08:29Recap and related codes

Quick recap. P0340 means the computer did not receive a valid changing signal from camshaft position sensor A; it does not automatically mean the sensor failed. Verify cranking voltage and crank RPM, test sensor power and ground, scope the cam signal, inspect its target and timing, then follow the waveform to the PCM before buying parts.

If your scan tool showed a related code alongside this one, check those too: P0341, P0342, P0343, P0016.

Codes are on screen and linked below.