P0399 is an OBD-II trouble code that points to a problem with the engine’s bank 2 camshaft position sensor “B” signal. In simple terms, your ECU is seeing a cam signal that’s weak, noisy, or out of range and can’t reliably control valve timing and fuel injection on that bank. You might notice rough running, poor performance, or just a check engine light. This isn’t usually an instant “engine killer,” but it can lead to misfires, higher fuel use, and long-term damage if you ignore it. Let’s walk through what it means and how to fix it.
What Does P0399 Mean?
P0399 is defined as “Camshaft Position Sensor ‘B’ Circuit Intermittent (Bank 2)” or “Camshaft Position Sensor ‘B’ Circuit High/Intermittent (Bank 2)” depending on the manufacturer. Bank 2 is the cylinder bank that does not contain cylinder #1, and sensor “B” is usually the exhaust cam sensor on dual overhead cam (DOHC) engines.
The ECU expects a clean, consistent signal from this sensor as the camshaft rotates. When the signal voltage is unstable, drops out, or spikes intermittently, the ECU flags P0399. That can be due to a failing sensor, wiring issues, or sometimes a mechanical timing or VVT (variable valve timing) problem.
Quick Reference
- Code: P0399 – Camshaft Position Sensor “B” Circuit Intermittent (Bank 2)
- Severity: Moderate – can lead to drivability issues and misfires
- Common causes: Bad cam sensor, wiring faults, oil contamination, VVT issues
- Typical symptoms: Check engine light, rough idle, hard start, reduced power
- Driveability: Often drivable short-term, but repair soon to avoid damage
Real-World Example / Field Notes
In the shop, I see P0399 fairly often on higher-mileage V6 and V8 engines with dual cam sensors per bank. A common pattern: the owner comes in complaining of a rough idle and occasional stumble on acceleration, but the car “drives mostly fine.” Scan shows P0399 and sometimes a random misfire code. On inspection, the bank 2 exhaust cam sensor wiring is brittle from heat, and the connector has light oil intrusion. Replacing the sensor, cleaning the connector, and securing the harness away from the exhaust usually solves it. When it doesn’t, the next culprit is often a sticky VVT solenoid causing the cam timing to fluctuate.
Symptoms of P0399
- Check engine light on: The MIL will usually illuminate and store P0399 as a current or pending code.
- Rough idle: Unstable cam timing on bank 2 can cause a shaky or hunting idle.
- Hard starting: The ECU may struggle to sync crank and cam signals, leading to extended cranking.
- Loss of power: Incorrect valve timing can reduce engine power, especially under load.
- Poor fuel economy: Inefficient combustion from mistimed valve events wastes fuel.
- Intermittent misfires: You may feel occasional jerks or hesitation, often with no obvious pattern.
- Increased emissions: A failing cam signal can cause rich or lean conditions and higher tailpipe emissions.
Common Causes of P0399
Most Common Causes
- Failed camshaft position sensor “B” (bank 2): Internal sensor failure, heat damage, or contamination can cause intermittent signal loss.
- Damaged wiring or connector: Chafed, melted, corroded, or oil-soaked wiring between the sensor and ECU is extremely common, especially near the exhaust manifold.
- Poor electrical grounds or power supply: Weak ground or low reference voltage can make the signal noisy or unstable.
- Oil contamination in sensor area: Leaking valve cover gaskets can let oil soak the sensor and connector, affecting the signal.
- VVT (variable valve timing) issues on bank 2: A sticking VVT solenoid or phaser can cause erratic cam movement that looks like an intermittent sensor fault.
Less Common Causes
- Timing chain/belt stretch or jump: Excessive slack or a skipped tooth can alter cam timing enough to confuse the ECU.
- Reluctor wheel damage: A cracked, bent, or dirty cam trigger wheel can distort the sensor signal.
- ECU/PCM internal fault: Rare, but a failing driver or internal circuit can misread a good sensor signal.
- Aftermarket modifications: Poorly installed remote starters, piggyback tuners, or wiring add-ons can introduce noise into the cam signal circuit.
- Incorrect or low-quality replacement sensor: Cheap aftermarket sensors sometimes produce weak or unstable signals the ECU doesn’t like.
Diagnosis: Step-by-Step Guide
You’ll want a basic tool set, a quality scan tool with live data (and ideally Mode $06), a digital multimeter, and if possible an oscilloscope for viewing the cam signal waveform. A service manual or wiring diagram for your specific vehicle is also very helpful.
- Confirm the code and check for companions. Scan for all stored and pending codes. Note any related cam/crank, VVT, or misfire codes (like P030X, P001X–P002X). Clear the codes and see if P0399 returns quickly or only under certain conditions.
- Visual inspection of sensor and harness. Locate the bank 2 camshaft position sensor “B” (often at the rear or side of the cylinder head). Check for broken clips, oil-soaked connectors, melted insulation, or wires rubbing on brackets or exhaust components.
- Check connector and terminals. Unplug the sensor and inspect the pins for corrosion, bent terminals, or moisture. Lightly tug each wire to ensure it’s not broken inside the insulation.
- Basic electrical tests. With the key on, use a multimeter to verify proper reference voltage (usually 5V), ground, and signal wire continuity between the sensor and ECU. Repair any open or short circuits.
- Monitor live data. On your scan tool, watch camshaft position data and VVT commanded/actual angles for bank 2 while idling and gently revving. Intermittent dropouts or erratic readings on sensor “B” point to a sensor or wiring issue.
- Scope the cam signal (if available). Using an oscilloscope, compare the waveform of bank 2 sensor “B” to bank 1 or sensor “A.” Look for missing pulses, noise, or irregular patterns when the code sets.
- Inspect oil condition and level. Dirty or low engine oil can affect VVT operation. If oil is sludged or overdue, change it with the correct viscosity and quality filter.
- Check VVT components on bank 2. If the sensor and wiring test good, remove and inspect the bank 2 VVT solenoid for debris or sticking. Some engines allow phaser testing with a scan tool by commanding different cam angles.
- Mechanical timing check. If symptoms are severe or you hear chain/belt noise, verify timing marks and chain/belt condition. Excessive slack or misalignment can cause intermittent cam signal issues.
- Substitute a known-good sensor. As a final check, install a high-quality replacement sensor and retest. If the problem disappears, the original sensor was likely failing intermittently.
Pro tip: When you have intermittent cam sensor codes like P0399, gently wiggle the harness and connector while watching live data or the scope. If the signal glitches when you move the wiring, you’ve likely found the problem area.
Possible Fixes & Repair Costs
Most P0399 repairs are straightforward once you pinpoint the cause. Common fixes include:
- Replace bank 2 camshaft position sensor “B”: Often the primary fix. Parts typically run $40–$180 depending on brand and vehicle; labor is usually 0.5–1.0 hour.
- Repair or replace wiring/connector: Splicing in new wire, replacing terminals, or installing a pigtail connector can cost $100–$350 depending on access and harness length.
- Clean or replace VVT solenoid (bank 2): Cleaning may be low cost; replacement parts are commonly $80–$250 plus 0.7–1.5 hours labor.
- Oil change and leak repair: Fresh oil and filter plus fixing a valve cover leak that’s soaking the sensor can run $80–$400.
- Timing chain/belt service: If mechanical timing is off, full timing service can range from $600 to over $1,800 depending on engine design.
Overall, typical P0399 repair costs fall between about $150 and $600 when it’s just a sensor or minor wiring issue. Costs climb when timing components, VVT phasers, or major oil leak repairs are involved. Labor rate, engine layout, and parts quality all affect the final bill.
Can I Still Drive With P0399?
In many cases, you can still drive with P0399 for a short period, especially if the engine runs fairly smoothly and the light is steady (not flashing). However, it’s not something you should ignore for weeks. An intermittent cam signal can lead to misfires, poor fuel economy, and increased emissions. If you notice rough running, loss of power, or a flashing check engine light, reduce driving, avoid heavy loads, and get it diagnosed as soon as possible to prevent further damage.
What Happens If You Ignore P0399?
Ignoring P0399 long-term can cause more frequent misfires, carbon buildup, and potential damage to the catalytic converters from unburned fuel. If the root cause is a worsening wiring issue or failing timing components, you could eventually end up with a no-start condition or serious internal engine damage. Fixing it early is almost always cheaper than waiting until it escalates.
Related Codes
- P0364 – Reserved
- P0363 – Misfire Detected Fueling Disabled
- P0362 – Ignition Coil “L” Primary/Secondary Circuit
- P0361 – Ignition Coil “K” Primary/Secondary Circuit
- P0360 – Ignition Coil “J” Primary/Secondary Circuit
- P0359 – Ignition Coil “I” Primary/Secondary Circuit
- P0358 – Ignition Coil “H” Primary/Secondary Circuit
- P0357 – Ignition Coil “G” Primary/Secondary Circuit
- P0356 – Ignition Coil “F” Primary/Secondary Circuit
- P0355 – Ignition Coil “E” Primary/Secondary Circuit
Key Takeaways
- P0399 points to an intermittent or unstable signal from the bank 2 camshaft position sensor “B,” usually the exhaust cam sensor.
- Common causes include a failing sensor, damaged wiring, oil contamination, and VVT or timing issues.
- Symptoms range from a simple check engine light to rough idle, hard starting, and loss of power.
- Diagnosis should include visual inspection, electrical testing, live data, and ideally waveform analysis.
- Most repairs are moderate in cost if handled early; ignoring the code can lead to misfires and catalytic converter damage.
Vehicles Commonly Affected by P0399
P0399 shows up most often on modern V6 and V8 engines that use separate intake and exhaust cam sensors on each bank. You’ll commonly see it on:
- GM/Chevrolet/GMC: 3.6L V6, 5.3L and 6.2L V8 engines in trucks, SUVs, and crossovers.
- Chrysler/Dodge/Jeep/Ram: Pentastar V6 and HEMI V8 engines with VVT.
- Ford/Lincoln: Some Duratec and EcoBoost V6 engines with dual cam sensors per bank.
- Hyundai/Kia: V6 engines in SUVs and sedans using separate “A” and “B” cam sensors.
- Luxury brands: Certain BMW, Mercedes-Benz, and Lexus V6/V8 engines with advanced VVT systems.
The exact layout and naming of sensor “B” can vary by manufacturer, so always verify bank and sensor location using a service manual or reliable repair information.
FAQ
Can I clear P0399 and keep driving if the car feels fine?
You can clear the code once to see if it was a one-time glitch, but if P0399 comes back, you shouldn’t ignore it. An intermittent cam signal usually gets worse over time. Keep an eye on how the engine runs and schedule diagnosis soon, even if it still feels okay.
Is P0399 caused by a bad timing chain?
It can be, but that’s less common than a bad sensor or wiring fault. A stretched or jumped timing chain can cause unstable cam timing that triggers P0399, often along with VVT and misfire codes. If you hear rattling on cold starts or see multiple timing-related codes, have the timing components inspected.
How do I know which side is bank 2 for P0399?
Bank 2 is the cylinder bank that does not contain cylinder #1. The exact side varies by engine and drivetrain layout. On many V6/V8 engines, bank 2 is the opposite side of bank 1, but you should confirm using a service manual, under-hood label, or reliable online repair data for your specific engine.
Can a bad cam sensor damage my engine?
The sensor itself doesn’t directly damage the engine, but running with a bad cam signal can cause misfires, poor combustion, and extra stress on the catalytic converters. If left long enough, that can lead to expensive exhaust and engine repairs. Replacing a failing sensor early is cheap insurance.
Do I need an OEM sensor to fix P0399?
You don’t always need OEM, but you should use a high-quality brand that meets or exceeds OE specs. Cheap no-name sensors are a common cause of repeat cam sensor codes. If the vehicle is picky about sensor signals (many are), an OEM or top-tier aftermarket part is worth the small extra cost.