P0393 Camshaft Position Sensor "B" Circuit High Input (Bank 2)

The P0393 diagnostic trouble code means the engine control module (ECM/PCM) has detected an abnormally high electrical signal from the Camshaft Position Sensor “B” circuit on Bank 2.

This is primarily an electrical circuit fault. The code does not automatically mean that the camshaft position sensor itself is defective.

A high signal can be caused by a faulty sensor, a short to voltage, damaged wiring, a connector problem, a reference-voltage issue, a ground problem, or an abnormal signal caused by the camshaft trigger mechanism. On some engines, problems with variable valve timing can also affect the signal and create additional synchronization faults.

Understanding “Sensor B” and “Bank 2”

Two terms in P0393 need particular attention: “B” and “Bank 2.”

Bank 2 refers to the cylinder bank that does not contain cylinder number 1.

On a V6, V8, or another multi-bank engine, the engine is divided into two cylinder banks. Bank 2 is not universally the left or right side because that depends on the engine's physical design.

Sensor B is also manufacturer-specific.

On many engines, Sensor B is associated with a particular camshaft, often the exhaust camshaft, but this is not a universal rule. Engines equipped with separate intake and exhaust camshafts, variable valve timing, or multiple camshaft sensors can have different naming strategies.

Therefore, the exact location of the P0393 sensor should be confirmed using the vehicle's wiring diagram or service information.

What Does “High Input” Mean?

The phrase “High Input” refers to the electrical signal detected by the ECM/PCM, not necessarily to high engine speed or a physically high camshaft position.

The ECM continuously monitors the camshaft sensor circuit.

If the signal remains at a voltage or electrical state higher than the expected operating range, the module can set P0393.

Possible causes include:

• Signal wire shorted to battery voltage

• Open or poor ground circuit

• Faulty sensor

• Damaged connector

• Reference-voltage problem

• Wiring damage

• Incorrect sensor installation

• Electrical interference

• Trigger-wheel or camshaft-related problems

An important point is that an open circuit can sometimes produce a high input reading, depending on the sensor design and how the ECM biases the circuit.

How the Camshaft Position Sensor Works

The camshaft position sensor monitors a rotating target attached to or integrated with the camshaft.

As the camshaft rotates, teeth, slots, magnets, or other target features pass the sensor.

The sensor converts this movement into an electrical signal.

The ECM uses that signal to determine the camshaft's position relative to the crankshaft.

This synchronization is essential because the engine needs to know which cylinder is approaching a particular point in its four-stroke cycle.

If the camshaft signal becomes incorrect or unreliable, the ECM may have difficulty determining:

• Injection timing

• Ignition timing

• Camshaft position

• VVT position

• Cylinder synchronization

• Engine startup position

Common Causes of P0393

Faulty camshaft position sensor

The sensor itself can develop an internal electrical fault and produce an abnormally high output.

Heat, vibration, oil contamination, age, and repeated thermal cycling can eventually damage the sensor.

However, the sensor should not automatically be replaced simply because P0393 is stored.

Signal wire shorted to voltage

A damaged signal wire may contact a battery-voltage or another powered circuit.

This can force the camshaft sensor signal higher than expected.

This is especially important when the code appears immediately after wiring repairs or engine work.

Open or damaged wiring

A broken wire can interrupt the intended sensor circuit.

Depending on the sensor design, the ECM's internal pull-up or bias circuit can cause the signal to remain high when the circuit is open.

Connector corrosion

Oil, moisture, dirt, or corrosion inside the connector can alter the electrical characteristics of the circuit.

A connector can look relatively clean externally while its terminals have poor electrical contact.

Loose or damaged terminals

A terminal that has lost its proper tension can intermittently disconnect the sensor from the ECM.

This can create unstable camshaft signals and may produce additional synchronization codes.

Ground circuit problem

Some camshaft sensors require a dedicated sensor ground.

If the ground circuit has excessive resistance or becomes open, the signal can become abnormal.

A simple continuity check is not always sufficient because a circuit can show continuity while still having excessive resistance under operating conditions.

Reference voltage problem

Depending on the sensor architecture, a reference-voltage circuit may be involved.

A problem shared with other sensors can sometimes produce multiple DTCs simultaneously.

If several sensors suddenly report abnormal signals, a shared reference or ground circuit should be considered.

Incorrect sensor

A sensor that looks physically identical may not have the same electrical characteristics or signal strategy.

Installing an incorrect or incompatible aftermarket sensor can cause an abnormal signal.

Camshaft trigger/reluctor problem

The sensor can be electrically healthy while the target it reads is damaged, loose, incorrectly positioned, or contaminated.

Possible problems include:

• Damaged reluctor teeth

• Missing target features

• Loose trigger wheel

• Incorrect camshaft component

• Excessive mechanical movement

• Foreign material affecting the signal

Variable valve timing problem

On engines with VVT, the actual camshaft position can change relative to the crankshaft.

A sticking VVT actuator, oil-control problem, incorrect oil pressure, or mechanical timing problem can produce additional camshaft correlation faults.

However, a pure circuit-high condition should first be investigated electrically rather than assuming that a mechanical timing problem is responsible.

ECM/PCM fault

A failed ECM input circuit is possible but relatively uncommon.

The module should be considered only after the sensor, wiring, connector, power, ground, reference circuits, and signal have been properly tested.

Symptoms of P0393

The symptoms can range from almost unnoticeable to severe.

Possible symptoms include:

• Check Engine Light

• Difficult starting

• Extended cranking

• Engine may crank but not start

• Rough idle

• Engine hesitation

• Poor acceleration

• Reduced engine power

• Increased fuel consumption

• Engine misfires

• Stalling

• Limp-home mode

• Variable valve timing problems

• Reduced performance

Some engines may continue running relatively normally even though P0393 is stored.

Other engines may have significant starting or synchronization problems because the ECM relies heavily on the camshaft signal.

Can P0393 Cause a No-Start?

Yes.

The severity depends on the engine's synchronization strategy.

If the ECM cannot obtain a reliable camshaft signal, it may have difficulty determining the correct relationship between the camshaft and crankshaft.

Some engines can fall back to a backup strategy and continue operating.

Others may have:

• Extended cranking

• Difficult starting

• Intermittent no-start

• Complete crank-no-start

If P0393 is accompanied by a crankshaft/camshaft correlation code, the diagnosis should include the timing relationship between the two signals.

Can P0393 Cause Misfires?

It can.

Incorrect camshaft information can affect injection and ignition timing.

If the ECM receives an incorrect camshaft position signal, combustion may occur at the wrong time or the system may lose proper cylinder synchronization.

This can result in:

• Misfires

• Rough running

• Hesitation

• Poor acceleration

• Stalling

However, a misfire should not automatically be blamed on the camshaft sensor. Ignition, fuel delivery, compression, and timing problems can independently cause misfire codes.

Diagnosing P0393 Correctly

A proper diagnosis should begin with the electrical circuit and then move toward mechanical causes if the electrical system checks out.

1. Scan for all DTCs

Do not diagnose P0393 in isolation.

Look for codes involving:

• Camshaft position

• Crankshaft position

• Cam/crank correlation

• Variable valve timing

• Engine misfire

• Sensor reference voltage

• Sensor ground

• Communication

Additional codes can dramatically change the diagnostic direction.

2. Check freeze-frame data

Freeze-frame information can show when P0393 was detected.

Useful information includes:

• Engine RPM

• Engine coolant temperature

• Battery voltage

• Engine load

• Vehicle speed

• Throttle position

• Camshaft position

• Crankshaft position

If the code appears only during engine startup, vibration, or high engine temperature, that can provide a useful clue.

3. Identify the exact Sensor B

Before testing anything, confirm which physical sensor the manufacturer identifies as Camshaft Position Sensor B, Bank 2.

Do not rely solely on generic diagrams found online.

The location and sensor designation can differ significantly between engines.

4. Inspect the connector

Check the sensor connector for:

• Corrosion

• Bent terminals

• Loose terminals

• Broken locking tabs

• Oil contamination

• Water intrusion

• Heat damage

The connector should make firm electrical contact with the sensor.

5. Inspect the wiring

Follow the harness away from the sensor.

Look for areas where it may have:

• Rubbed against the engine

• Been damaged by heat

• Been pinched

• Been stretched

• Been contaminated by oil

• Been repaired incorrectly

The wiring should also be inspected while gently moving the harness if the fault is intermittent.

6. Check the power, reference, and ground

Determine the sensor's circuit design before testing.

A Hall-effect sensor may use a power supply, ground, and signal.

A variable-reluctance sensor can have a different circuit arrangement.

The correct test procedure therefore depends on the sensor type.

There is no universal camshaft sensor voltage or resistance specification that can safely be applied to every vehicle.

Use the manufacturer's wiring diagram and specifications.

7. Check for a short to voltage

Because P0393 specifically identifies a high input, a short-to-voltage test is important.

The signal circuit should be checked for unintended contact with:

• Battery voltage

• Ignition voltage

• Another powered circuit

This can be particularly useful when the sensor itself tests normally.

8. Monitor the live camshaft signal

A scan tool may show camshaft synchronization or camshaft position data.

Observe the signal during:

• Cranking

• Idle

• Acceleration

• Engine warm-up

An oscilloscope is even more useful because it allows the technician to see the actual waveform rather than only the calculated value reported by the scan tool.

9. Compare camshaft and crankshaft signals

If the electrical circuit appears correct, compare the camshaft and crankshaft signals.

An abnormal relationship may indicate:

• Timing chain/belt problem

• Incorrect mechanical timing

• Damaged reluctor

• VVT problem

• Camshaft movement

• Installation error

This becomes particularly important if correlation codes are also present.

Why an Oscilloscope Can Be Useful

A multimeter can tell you whether voltage is present, but a camshaft position sensor produces a changing signal.

An oscilloscope can show:

• Signal amplitude

• Frequency

• Pulse shape

• Missing pulses

• Electrical noise

• Dropouts

• Timing relationship

For a P0393 diagnosis, this can be much more informative than measuring resistance alone.

A sensor can have a resistance value that appears acceptable while producing an incorrect signal under actual operating conditions.

Do Not Rely Only on Sensor Resistance

Resistance testing is particularly limited for modern camshaft sensors.

Some sensors are Hall-effect or electronically integrated devices where resistance measurements do not provide a meaningful pass/fail diagnosis.

Even where resistance testing is specified, the correct value depends on the exact sensor design.

Therefore, never replace a camshaft sensor simply because its resistance does not match a generic internet specification.

The manufacturer's testing procedure should be followed.

P0393 vs P0391 and P0392

The camshaft Sensor “B,” Bank 2 codes are related but describe different signal conditions.

P0391 – Camshaft Position Sensor “B” Circuit Range/Performance, Bank 2

The signal is present but does not behave within the expected operating range or performance parameters.

P0392 – Camshaft Position Sensor “B” Circuit Low Input, Bank 2

The ECM detects a signal that is lower than expected.

P0393 – Camshaft Position Sensor “B” Circuit High Input, Bank 2

The ECM detects a signal that is higher than expected.

The distinction is important because a P0393 diagnosis should pay particular attention to the signal circuit, reference/ground conditions, and possible short-to-voltage or open-circuit conditions.

P0393 vs P0348

Both codes involve a camshaft position sensor circuit reporting a high input, but they identify different sensor locations.

P0348 refers to Camshaft Position Sensor “A” Circuit High Input, Bank 2.

P0393 refers to Camshaft Position Sensor “B” Circuit High Input, Bank 2.

The exact physical sensors represented by A and B depend on the engine.

Can You Drive With P0393?

Driving with P0393 is not recommended for an extended period.

If the engine starts and runs normally with only a steady Check Engine Light, it may be possible to drive a short distance to a repair facility.

However, a camshaft signal problem can deteriorate and cause:

• Stalling

• No-start conditions

• Severe hesitation

• Misfires

• Reduced power

If the engine is stalling, running very roughly, or experiencing significant power loss, the vehicle should not be driven unnecessarily.

A Practical Diagnostic Sequence

A sensible approach to P0393 is:

P0393 detected → scan all codes → check freeze-frame → identify Sensor B on Bank 2 → inspect connector and wiring → verify sensor power/reference and ground → check signal circuit → test for short to voltage/open circuit → monitor live camshaft data → inspect signal waveform if necessary → compare camshaft and crankshaft synchronization → check mechanical timing/VVT if indicated → repair the confirmed cause → clear codes and verify the repair.

This approach prevents unnecessary sensor replacement.

Final Perspective

P0393 means the ECM/PCM has detected a high electrical input from Camshaft Position Sensor “B” on Bank 2.

The sensor itself may be faulty, but it is only one possibility.

Because the code specifically describes a high input, the diagnostic process should pay close attention to the sensor signal circuit, wiring condition, connector terminals, sensor power/reference and ground, and possible short-to-voltage conditions.

If the electrical circuit proves healthy, the investigation can then move toward the sensor's actual waveform, the camshaft trigger mechanism, mechanical timing, and variable valve timing system.

In other words, P0393 identifies an abnormal camshaft sensor signal—not a guaranteed bad sensor. The most reliable repair comes from determining why the ECM is seeing that high signal in the first place.