OBD-II trouble code
P0390: Camshaft Position Sensor 'B' Circuit (Bank 2)
The engine control module is not receiving a usable signal from the 'B' camshaft sensor on Bank 2. Because Bank 2 only exists on V and flat engines, this code cannot appear on a healthy inline four or inline six.
Quick facts
- System
- Powertrain
- Category
- Camshaft / Timing
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $130 – $700
- DIY difficulty
- Intermediate DIY
What does P0390 mean?
P0390 is the entry code for the fourth and last camshaft position sensor family in the generic OBD-II set. 'B' is the second camshaft on a bank, which on a dual overhead cam engine is almost always the exhaust camshaft, and Bank 2 is, by definition, the bank without cylinder 1 in it. The engine control module (ECM) expects a repeating pulse train from that sensor every camshaft revolution. When it sees nothing, or sees something it cannot interpret as a valid pattern, it stores P0390.
The first thing worth knowing about this code is a population fact that none of its Bank 1 counterparts can offer: Bank 2 does not physically exist on an inline engine. A four-cylinder or straight-six has one head, one bank, and therefore no P0390 to set. If a scan report shows P0390 on an inline engine, the realistic explanations are a misread code, a scan tool guessing at a manufacturer-specific definition, or a carmaker numbering its banks in a non-standard way. Confirm the code against factory information before ordering anything.
The second thing worth knowing is that P0390 is frequently a quiet code. Most V engines derive their fuel and spark synchronisation from the crankshaft sensor together with the intake camshaft sensor. Losing the Bank 2 exhaust cam signal costs the module its feedback for that one phaser, so the ECM parks that phaser at its default position and carries on. The engine starts, idles and drives. The owner is often convinced nothing is wrong because nothing feels wrong, and the honest answer is that the drivability loss is small while the emissions and efficiency loss is real and the warning lamp is not going away on its own.
Because it is the no-signal member of the family, P0390 covers three separate physical situations that behave identically from the module's point of view: a sensor that has stopped producing output, a circuit that never delivers what the sensor produced, and a reluctor or trigger wheel that has stopped passing anything for the sensor to detect. Those three have very different price tags, which is why the diagnosis below works outward from the connector rather than starting at the parts counter.
Common causes
- Failed 'B' camshaft position sensor on Bank 2
- Open or shorted wiring between the sensor and the ECM
- Corroded, backed-out or spread terminals in the sensor connector
- Loss of the sensor supply voltage or its ground return
- Damaged or loose reluctor / trigger wheel on the Bank 2 exhaust camshaft
- Metal debris on the sensor tip masking the trigger teeth
- Sensor installed with the wrong part number after a previous repair
- Rarely, a failed ECM input circuit
Symptoms
- Check engine light on with P0390 stored, often with no other complaint
- Slightly reduced fuel economy
- Loss of variable valve timing authority on Bank 2, felt as a small drop in midrange torque
- Longer cranking time on some applications
- Emissions test failure with readiness monitors incomplete
- Frequently accompanied by a Bank 2 exhaust cam timing performance code
Diagnostic steps
- 1.Confirm the code against the manufacturer's own definition before anything else. Generic and OEM definitions for the higher camshaft codes do not always agree on which sensor is meant.
- 2.Identify which physical sensor is 'B' on Bank 2 for this specific engine. On most DOHC V engines it is the exhaust cam sensor on the bank without cylinder 1, but confirm rather than assume.
- 3.Inspect the connector before testing anything. Pull it apart and look for green corrosion, spread terminals, and a lock tab that was never fully seated.
- 4.Key on, engine off, check for supply voltage and a good ground at the sensor connector. No supply means the fault is upstream of the sensor entirely.
- 5.Crank or run the engine and watch the sensor's signal on a scan tool live data list. A flat line with the engine turning confirms no signal is arriving.
- 6.If a scope is available, capture the waveform at the ECM connector rather than at the sensor. A clean signal at the sensor and nothing at the module localises the fault to the harness in one measurement.
- 7.Remove the sensor and inspect the tip for metal fuzz, and look at the reluctor teeth through the opening for damage or a ring that has spun on the camshaft.
- 8.Only replace the sensor once supply, ground, signal path and trigger wheel have all been shown to be good.
Repair cost
$130 – $700
A Bank 2 exhaust camshaft sensor is typically $40 to $180 for the part. On a longitudinal V8 with the sensor accessible from above, total cost is often $130 to $300. On a transverse V6 where Bank 2 sits against the firewall, the same part can take two to three times the labour, pushing the job toward $500 to $700. Harness and connector repair varies widely with how much of the loom has to be opened.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with camshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.