P0018

Powertrain
Generic (SAE)
Emissions

Severity

Get it looked at now

Cam-to-crank correlation faults sit on top of the engine's mechanical timing. A stretched or slack chain that is already outside the correlation window can skip a tooth, and on an interference engine that means valve-to-piston contact. Even where the cause is only a phaser or a sensor, the module may pull timing and fuelling back until it is fixed.

Safe to drive: Treat this as drive-it-to-the-shop only, not business as usual. Even if it runs smoothly and quietly, keep trips short, avoid high rpm and heavy load, and get it diagnosed before further driving — a chain can be quiet right up until it jumps. Any startup rattle, knock, low oil pressure warning or rough running means stop and tow.

Standard definition

Crankshaft Position - Camshaft Position Correlation (Bank 2 Sensor A)

In plain English

The engine computer compared the crankshaft signal to the bank 2 'A' camshaft signal and found the two out of step by more than the allowed amount. ('A' is usually the intake or front camshaft, but the assignment is defined by the manufacturer — confirm it in service information before ordering parts.) It has detected that cam timing on that bank is wrong; it has not identified what made it wrong.

The ECM derives actual camshaft angle in crank degrees from the phase relationship between the crankshaft reluctor pulses and the bank 2 'A' camshaft position sensor edges. With the variable valve timing phaser commanded to its default (park) position, that measured angle must fall inside a narrow calibrated window. P0018 sets when it does not, which can mean the chain has stretched or jumped, the phaser is not locking at park, oil pressure is insufficient to hold position, or the sensor signal itself is distorted.

How the car detected it

Every engine cycle the module counts crank pulses between camshaft sensor transitions and converts that count to a cam angle referenced to top dead centre. It runs the check with the oil control solenoid de-energized so the phaser should be mechanically locked at its park position. If the measured angle sits outside the allowed window — the width of that window is calibrated per engine and is not a generic value — for a set number of consecutive samples with the enable conditions met (engine running, rpm in range, and oil temperature above a threshold, measured or modelled, since many engines infer oil temperature from coolant temperature and run time), the code sets. MIL behaviour varies: some manufacturers treat cam-to-crank correlation as a one-trip fault and light the lamp on the first detection because of the mechanical risk, while others require two consecutive failed drive cycles. Check the strategy for the specific vehicle rather than assuming a second trip is needed.

A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.

Can I keep driving?

Safe to drive: Treat this as drive-it-to-the-shop only, not business as usual. Even if it runs smoothly and quietly, keep trips short, avoid high rpm and heavy load, and get it diagnosed before further driving — a chain can be quiet right up until it jumps. Any startup rattle, knock, low oil pressure warning or rough running means stop and tow.
Urgency: Get it looked at now
Will it pass emissions: No
If ignored: If the root cause is chain stretch or a worn tensioner, the chain can jump timing — that is a no-start at best and bent valves on an interference engine. A phaser stuck off-position causes rough running and misfire, which loads raw fuel into the catalytic converter. If low oil pressure is behind it, bearing wear is running in parallel with everything else.
Check engine light: Solid
Clearing the light: A completed drive cycle is normally required before the monitor re-runs and the light can clear.

Symptoms you may notice

Power loss especially in mid-rpm range
Possible rough idle or stalling
Increased fuel consumption

Many vehicles show no symptom at all beyond the warning light. The absence of a symptom does not mean the fault is not real.

Likely causes

These are the causes this code can have. For the order to work through them in, see what to check first.

#	Cause	How often	Component
1	Timing chain stretched (bank 2)	Very common	—
2	Bank 2 cam phaser failed	Common	—

Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.

What to check first

In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.

Engine oil level, condition and grade
Phasers and their lock pins are hydraulic. Low, sludged, or too-thin oil is the cheapest cause, and it is also what destroys chains and tensioners over time.
Freeze frame — rpm, coolant temperature, oil temperature if the vehicle reports it, and load when it set
A fault that only sets at cold idle points toward oil pressure or a phaser not locking. One present at all speeds and loads points toward mechanical timing. Not every engine has an oil temperature sensor, and freeze frame only carries the parameters that vehicle supports — coolant temperature and run time stand in for it where it is absent.
Any recent timing chain, phaser, cylinder head or cam sensor work
A chain or sprocket assembled one tooth off, or a sensor bracket left loose, sets this code immediately and makes further electrical testing a waste of time.
Cold start noise from the bank 2 side
A brief rattle for a second or two on startup is the classic sound of a chain tensioner bleeding down or a stretched chain slapping a guide.
Other stored codes
Companion codes for the other bank, for a cam sensor circuit, or for low oil pressure completely change the direction of the diagnosis.

How a shop diagnoses this

Record freeze frame and all stored codes before clearing anything
Tools Scan tool with freeze frame access
Capture the conditions the code set under, then note any companion codes — cam or crank sensor circuit faults, oil pressure codes, misfire codes on bank 2 cylinders. Do not clear codes until you have the data; you will need it to know whether the repair worked.
Verify engine oil level, condition and viscosity
Tools Dipstick, shop light
Check level on level ground with the engine off and settled. Look for sludge on the filler cap and dipstick. Confirm the grade in the sump matches what the manufacturer specifies — thinner or thicker than specified changes how fast a phaser responds and how well it locks.
Expected
Oil at full mark, clean, correct specified grade
Measure actual oil pressure with a mechanical gauge
Tools Mechanical oil pressure gauge and adapter, service information
Do not trust the dash lamp or the pressure sensor's scan data alone. Fit a mechanical gauge at the sender port and read pressure at idle and at raised rpm, with the engine at full operating temperature. Target pressures are vehicle-specific — look them up.
Compare commanded versus actual cam angle on both banks
Tools Scan tool with live data graphing
With the engine warm and idling, watch the desired and actual camshaft position PIDs for bank 1 and bank 2 side by side. With the solenoid at rest the actual angle should sit at that engine's specified park value — usually full retard for an intake phaser, but some engines use an intermediate lock position and exhaust phasers commonly park advanced, so confirm the park value in service information rather than assuming zero. A bank 2 actual angle away from the specified park value, or one that will not follow the command, localizes the fault. A bank 1 that behaves perfectly while bank 2 does not is a strong signal the fault is mechanical and bank-specific.
Expected
Both banks at their specified park value with the solenoid off, and both tracking command within the manufacturer's allowed error window
Command the bank 2 'A' camshaft solenoid with bidirectional control and watch the response
Tools Scan tool with bidirectional controls
Sweep the phaser with the scan tool at a steady warm idle. A phaser that will not move at all points at the solenoid, its screen, or an oil supply restriction. One that moves but overshoots or drifts points at the phaser itself.
Expected
Cam angle follows the command smoothly and returns to the specified park value when released
Scope the crank and bank 2 cam sensor signals together
Tools Two-channel lab scope, inductive or back-probe leads, reference waveform library
Capture both waveforms on the same timebase at idle and at raised rpm. You are looking for a cam edge that has shifted relative to the crank reference (mechanical timing) versus a signal that is ragged, dropping out, or amplitude-varying (sensor, reluctor, or wiring). Trigger patterns are vehicle-specific; compare to known-good reference waveforms for that engine.
Expected
Clean, stable pulses with a fixed phase relationship at all speeds
Verify mechanical timing directly
Tools Cam locking tools, service information, borescope where a cover can be avoided
If the electrical side is clean and the phaser responds, the chain has to be checked physically. Bring the engine to the manufacturer's timing reference position and compare marks, or use the specified cam locking tools. Access, marks and tool numbers vary by engine — use the service procedure for that vehicle.
Inspect chain, guides and tensioner if timing is off
Tools Hand tools, service information
Where the marks are out or slack is excessive, the tensioner, guides and chain all need assessment as a set. Replacing a stretched chain onto worn guides puts the same fault straight back.

Possible repairs and what they cost

Repair	Only after you confirm	Typical cost	Who
Oil and filter change with the correct specified viscosity, then re-test	Oil found low, degraded, sludged or the wrong grade, with mechanical timing verified acceptable	$60–$180	DIY
Bank 2 'A' camshaft oil control valve (solenoid) and screen replacement	Phaser fails to move on bidirectional command, or the solenoid screen is found blocked, with chain timing verified correct	$150–$500	DIY
Bank 2 'A' camshaft phaser replacement	Oil pressure and solenoid delivery confirmed good and chain timing correct, but the phaser will not lock at its specified park position or shows excessive lock pin play	$700–$2,400	Shop
Timing chain set replacement — chain(s), guides and tensioner. Many V engines use a single chain or a primary-plus-secondary arrangement, so the work is usually not confined to one bank even when only one bank set the code	Timing marks found out of position, measured chain slack beyond specification, or a scope capture showing the cam edge shifted against the crank reference with the phaser at park	$1,200–$3,800	Shop
Camshaft or crankshaft position sensor replacement	Scope capture shows a distorted, dropping-out or amplitude-varying signal while mechanical timing is verified correct	$150–$420	DIY
Wiring harness or connector repair at the cam or crank sensor	Chafe, corrosion or a spread terminal found, and the signal returns clean on the scope after repair	$100–$400	DIY
Engine oil pressure repair (pump, pickup screen, or wear-related low pressure)	Mechanical gauge reads below the manufacturer's specification at operating temperature	$700–$3,000	Shop

Expect $110 to $220 for diagnosis on top of the repair; correlation codes take scope and mechanical verification time, and a shop that skips that is guessing. Chain work on a V-configuration engine varies enormously with access — a transverse V6 in a front-drive car can double the labour versus a longitudinal engine with room in front of it, and because most V engines share a chain between banks the job is rarely priced per bank.

Common mistakes with this code

Replacing the camshaft position sensor first because it is the cheapest part in the code description. A correlation code is far more often mechanical or hydraulic than it is a sensor.
Assuming bank 2 is a fixed physical side of the engine. Bank 2 is simply the bank that does not contain cylinder 1, and which side that is varies by make and even by engine within a make.
Clearing the code and calling it fixed because the light stays off for a day. Correlation monitors usually require specific enable conditions, so a real fault can take several drive cycles to reappear.
Ignoring oil condition because the engine 'does not use oil'. Sludge that blocks a phaser feed passage does not show as consumption.
Replacing the chain without replacing guides and tensioner, or without addressing why the oil was degraded in the first place — the same fault comes back.

Components involved

Sources

Definition: Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
Diagnostic guidance: Written and reviewed in-house. See our editorial policy.
Review status: Reviewed

Found something wrong? Tell us — we publish corrections.

Engine oil level, condition and grade

Freeze frame — rpm, coolant temperature, oil temperature if the vehicle reports it, and load when it set

Any recent timing chain, phaser, cylinder head or cam sensor work

Cold start noise from the bank 2 side

Other stored codes

Record freeze frame and all stored codes before clearing anything

Verify engine oil level, condition and viscosity

Measure actual oil pressure with a mechanical gauge

Compare commanded versus actual cam angle on both banks

Command the bank 2 'A' camshaft solenoid with bidirectional control and watch the response

Scope the crank and bank 2 cam sensor signals together

Verify mechanical timing directly

Inspect chain, guides and tensioner if timing is off