P0390 Camshaft Position Sensor "B" Circuit (Bank 2)

P0390 is an OBD-II diagnostic trouble code indicating that the engine control module (ECM/PCM) has detected a problem in the electrical circuit associated with Camshaft Position Sensor “B” on Bank 2.

The important point is that P0390 is fundamentally a circuit fault code. It does not automatically mean that the camshaft sensor itself has failed, nor does it prove that the engine's mechanical timing is incorrect.

The exact definition of Camshaft Position Sensor “B” can vary between manufacturers. On many engines, Sensor B refers to the sensor monitoring the second camshaft or the exhaust camshaft, but this is not universal. The manufacturer's wiring diagram and service information should always be used to identify the correct sensor.

What Does Camshaft Position Sensor “B” Do?

The camshaft position sensor tells the ECM where the camshaft is in its rotation. The ECM uses this information together with the crankshaft position signal to determine things such as:

• Which cylinder is approaching the combustion event

• When to operate the fuel injectors

• Ignition timing

• Variable valve timing (VVT) control

• Camshaft-to-crankshaft synchronization

• Engine start and synchronization strategy

On a modern engine, the camshaft signal is therefore much more than a simple RPM measurement. The ECM needs an accurate camshaft signal to know where the engine is in its four-stroke cycle.

If the signal from Sensor B on Bank 2 becomes unavailable or electrically incorrect, the ECM may have difficulty maintaining proper synchronization.

What Does “Bank 2” Mean?

Bank 2 normally refers to the cylinder bank that does not contain cylinder #1 on a multi-bank engine.

For example, on a V6 or V8 engine there are two cylinder banks. One is Bank 1 and the other is Bank 2.

On a four-cylinder inline engine, there is normally only one bank, so a Bank 2 camshaft sensor code would generally indicate that the vehicle uses a different engine architecture or that the code definition is manufacturer-specific.

This is another reason why the exact vehicle application matters when diagnosing P0390.

What Does “Circuit” Mean in P0390?

The word “Circuit” is particularly important.

P0390 does not necessarily mean:

“The camshaft position sensor is bad.”

It means the ECM has detected a problem somewhere in the electrical circuit associated with that sensor.

Depending on the vehicle, the circuit may include:

• Camshaft position sensor

• Sensor power supply

• Sensor ground

• Signal wire

• Connector

• Wiring harness

• Shielding or reference circuit

• Camshaft reluctor/trigger target

• Integrated VVT or camshaft actuator electronics

• ECM/PCM

A broken wire can therefore set P0390 even when the sensor itself is perfectly good.

Common Causes of P0390

Several faults can produce this code.

Faulty camshaft position sensor

The sensor can fail internally, become temperature-sensitive, or produce an abnormal signal. Some sensors work correctly when cold and begin failing after the engine compartment becomes hot.

Damaged wiring

A wire may be broken internally, rubbed through against the engine, melted by exhaust heat, or stretched near the connector.

This is particularly important with intermittent camshaft problems because the wiring can look completely normal while the conductor inside is damaged.

Loose or corroded connector

Moisture, oil contamination, corrosion, loose terminals, or poor terminal tension can interrupt the sensor signal.

A connector that looks clean externally can still have a terminal that does not make reliable electrical contact.

Power or ground problem

Depending on sensor design, the camshaft sensor may require a dedicated supply voltage and ground. A poor ground or missing supply can prevent the sensor from producing a usable signal.

Short circuit

The signal wire may be shorted to ground, another circuit, or a voltage supply.

Damaged camshaft trigger target

Some systems use a reluctor wheel, trigger plate, tone ring, or other target attached to the camshaft. If this component is damaged, loose, incorrectly installed, or physically displaced, the sensor may be unable to produce the expected signal.

Incorrect sensor installation

An incorrectly installed sensor, excessive sensor-to-target clearance, damaged mounting point, or wrong sensor part number can create signal problems.

VVT-related problems

Variable valve timing can affect the relationship between the camshaft signal and the crankshaft signal. However, a VVT problem should not automatically be blamed for P0390.

The electrical circuit should be checked first when the diagnostic code specifically points to a circuit fault.

ECM/PCM fault

An ECM problem is possible, but it should generally be considered only after the sensor, wiring, power, ground, signal, and trigger target have been properly tested.

Symptoms You May Notice

The symptoms depend heavily on how severe the signal problem is.

Possible symptoms include:

• Check Engine Light

• Difficult starting

• Extended cranking

• Engine that starts and stalls

• Rough idle

• Hesitation during acceleration

• Reduced engine performance

• Poor fuel economy

• Misfires

• Reduced VVT performance

• Engine entering a reduced-power strategy

• In some cases, no obvious drivability symptoms other than the warning light

Some engines can continue running using the crankshaft sensor and substitute strategies when the camshaft signal is lost. Others rely much more heavily on camshaft synchronization and may have significant starting or running problems.

How P0390 Should Be Diagnosed

A good diagnosis starts with the vehicle-specific circuit, rather than immediately replacing the camshaft sensor.

First, scan all available modules and record the freeze-frame information. Look for other codes related to camshaft position, crankshaft position, VVT, synchronization, or low system voltage.

Then identify exactly which physical sensor the manufacturer calls Camshaft Position Sensor B, Bank 2.

Inspect the sensor and connector carefully. Look for:

• Oil contamination

• Water intrusion

• Corrosion

• Bent terminals

• Loose terminals

• Damaged insulation

• Harness rubbing

• Exhaust heat damage

• Signs of previous repairs

The wiring should then be tested according to the manufacturer's wiring diagram.

Depending on the sensor design, this may involve checking:

• Supply voltage

• Ground quality

• Signal voltage

• Signal continuity

• Short-to-ground

• Short-to-power

• Voltage drop

• Terminal integrity

Simply checking continuity with a multimeter is not always enough. A wire can show continuity with almost no load but develop excessive resistance when the circuit is actually operating.

Hall-Effect and Variable-Reluctance Sensors Are Different

The sensor technology matters.

Many modern camshaft sensors are Hall-effect or similar active sensors that receive an electrical supply and produce a digital signal.

Older or different designs may use variable-reluctance sensors that generate their own AC signal.

Because of this, there is no universal camshaft sensor resistance or voltage specification that can safely be applied to every vehicle.

Testing procedures should come from the manufacturer's service information.

Use Live Data When Available

If the scan tool provides camshaft synchronization or camshaft position data, compare the commanded/expected behavior with the actual signal.

An oscilloscope is even more useful when P0390 is difficult to reproduce.

A scope can reveal:

• Missing signal pulses

• Distorted waveforms

• Electrical noise

• Signal dropouts

• Incorrect amplitude

• Timing irregularities

• Problems that only appear during cranking or acceleration

Comparing the Bank 2 Sensor B waveform with the crankshaft position signal can also help determine whether the problem is electrical or related to mechanical synchronization.

Could a Timing Chain Cause P0390?

A timing problem can certainly create camshaft-related diagnostic codes, but P0390 by itself does not prove that the timing chain is faulty.

A stretched timing chain, incorrectly installed timing components, damaged camshaft reluctor, or VVT problem may produce additional correlation or synchronization codes.

If the sensor has a clean electrical signal but the camshaft signal is physically occurring at the wrong time relative to the crankshaft, mechanical timing becomes much more relevant.

This distinction is important because replacing the camshaft sensor will not repair an engine whose mechanical timing is incorrect.

P0390 vs P0391, P0392, P0393 and P0394

These codes can look similar but describe different types of problems.

P0390 indicates a general circuit malfunction involving Camshaft Position Sensor B on Bank 2.

P0391 generally indicates that the Sensor B signal is outside its expected range or performance.

P0392 indicates a low input signal from Sensor B.

P0393 indicates a high input signal from Sensor B.

P0394 indicates an intermittent signal problem from Sensor B on Bank 2.

That distinction matters during diagnosis. For example, P0392 may lead you toward a signal pulled low, while P0394 makes an intermittent connector or wiring fault particularly important.

Is P0390 Caused by a Bad Camshaft Sensor?

It can be, but the code alone is not enough to make that conclusion.

If testing shows that the sensor has correct power and ground but produces an incorrect or missing signal, replacing the sensor may be the correct repair.

However, if the sensor has no power, replacing it will not solve the problem.

Likewise, if the signal wire is damaged, the connector has poor terminal tension, or the camshaft trigger target is damaged, installing a new sensor can leave P0390 completely unchanged.

This is why P0390 should be treated as a circuit diagnosis rather than a parts-replacement diagnosis.

What About Oil and VVT Problems?

Engine oil condition can be important on engines equipped with variable valve timing. Low oil level, incorrect oil viscosity, restricted oil passages, or a malfunctioning VVT actuator can affect camshaft positioning.

But an oil-related VVT problem should not automatically be interpreted as an electrical Sensor B circuit failure.

If P0390 appears together with camshaft timing or VVT codes, the complete system should be evaluated. If P0390 is the only code and the sensor circuit has an obvious electrical fault, the electrical problem deserves priority.

Can You Drive With P0390?

If the engine starts and runs normally, the vehicle may remain driveable for a limited period. However, continued driving is not ideal.

A worsening camshaft signal problem can eventually cause:

• Starting problems

• Stalling

• Poor acceleration

• Increased fuel consumption

• Misfires

• Reduced engine performance

If the engine is difficult to start, stalls unexpectedly, runs very roughly, or develops severe power loss, it should be diagnosed before continued driving.

The Most Important Point About P0390

P0390 should not be interpreted simply as “replace the Bank 2 camshaft sensor.”

The code tells you that the ECM has detected a malfunction in the electrical circuit associated with Camshaft Position Sensor B on Bank 2. The actual cause could be the sensor, wiring, connector, power supply, ground, signal circuit, trigger target, VVT-related mechanical condition, or—in much less common cases—the ECM itself.

The most reliable repair comes from determining what the ECM is actually seeing on the Sensor B circuit, rather than replacing components based only on the stored fault code.