The P0017 code is one of the few check-engine faults I never treat as a simple nuisance. It tells you the engine control unit thinks the crankshaft and camshaft are no longer agreeing on where the engine is in its cycle, which can point to anything from low oil to a slipped timing chain. This guide breaks down what the fault means, what symptoms matter, how I would diagnose it, and what repairs usually cost in the UK.
The quickest way to read this fault
- P0017 usually points to a crankshaft-to-camshaft correlation problem on bank 1, often on the exhaust cam side on many engines.
- The cause can be mechanical, electrical, or oil-related, and the difference matters because the fix can range from a simple sensor repair to a timing job.
- A rattling start-up, rough idle, hard starting, or obvious power loss makes me suspect more than a minor wiring issue.
- If the engine is misfiring badly, refusing to start, or making chain-like noise, I would treat it as a tow-it situation rather than a drive-it-and-see fault.
- In the UK, a basic diagnostic check is usually far cheaper than the repair itself, but timing-chain work can move into four figures on some cars.
What the fault really means
On a healthy engine, the crankshaft and camshaft move in a very precise relationship. The crank drives the pistons, while the cam controls valve opening, so the engine computer watches both signals to confirm the engine is timed correctly. When the signals drift beyond the allowed window, it stores a P0017 and switches on the engine management light.The important detail is that this is a correlation fault, not automatically a bad sensor fault. The ECU is saying the relationship between the two signals looks wrong, but that can happen because a chain has stretched, a belt has jumped, a cam phaser is sticking, oil pressure is poor, or a sensor signal is noisy.
| Code | What it usually signals | How I read it |
|---|---|---|
| P0016 | Crank/cam correlation issue on bank 1, sensor A | Often points toward the intake cam or general timing alignment |
| P0017 | Crank/cam correlation issue on bank 1, sensor B | Often points toward the exhaust cam side on many engines |
| P0018 | Crank/cam correlation issue on bank 2, sensor A | The same logic, but on the opposite bank |
| P0019 | Crank/cam correlation issue on bank 2, sensor B | Useful when the engine has two banks and two cam signals |
Bank 1 means the side of the engine with cylinder 1, and sensor B is commonly the exhaust cam signal on many engines, although manufacturers do not always label things the same way. That is why I do not jump straight to a part number. Once that distinction is clear, the symptoms tell you how urgent the fault is.
Symptoms that separate a nuisance code from a timing problem
The warning light on its own is not the whole story. Some cars only log the code and continue to run fairly smoothly, while others become obviously unhappy because the timing error affects combustion and valve control.- Hard starting when the engine cranks longer than normal before firing.
- Rough idle with shaking, uneven revs, or a slightly lumpy sound.
- Loss of power especially under load or during overtaking.
- Poor fuel economy because combustion timing is no longer clean.
- Rattling on cold start which often makes me think about chain wear, tensioner issues, or a phaser problem.
- Misfire or stalling in more serious cases, especially if the timing has shifted far enough to upset valve events.
If the engine starts to rattle, stalls, or struggles to fire, I stop thinking of this as a code-reading exercise and start treating it as a timing integrity problem. That leads directly into the causes, because the fix depends on what moved out of alignment in the first place.
Why this fault appears in the first place
In practice, I group the causes into three buckets. That keeps the diagnosis honest and stops the repair from turning into guesswork.
- Mechanical timing wear such as a stretched chain, worn guides, a weak tensioner, or a belt that has jumped a tooth. This is the classic serious cause, because the engine is no longer physically timed the way it should be.
- VVT problems such as a sticking cam phaser or a sluggish oil control solenoid. Variable valve timing can move the cam enough to trigger the fault even when the chain or belt is not fully out of place.
- Oil issues including low oil level, the wrong viscosity, dirty oil, or sludge. VVT systems rely on clean oil flow, so a lubrication issue can become a timing complaint very quickly.
- Electrical faults such as a failing camshaft or crankshaft sensor, damaged wiring, corroded connectors, or poor grounding. These can imitate a mechanical problem by corrupting the signal the ECU is reading.
- Recent repair error after a timing job, chain replacement, head work, or sensor swap. If the fault appeared immediately after maintenance, I would inspect the work before assuming a component has failed again.
A recent belt or chain service is a useful clue. If the fault appeared straight after maintenance, the timing marks, tension, and cam-crank alignment deserve attention before anything else. With the likely cause bucket narrowed down, the next step is a proper diagnostic sequence.
How I would diagnose it in order
- Read all codes and freeze-frame data. Freeze-frame is just a snapshot of engine conditions when the fault was set, and it can tell you whether the issue happened at idle, under load, hot, or cold.
- Check the oil first. I look at level, condition, and whether the oil grade matches the engine spec. If the oil is low, dirty, or obviously wrong, I fix that before chasing hardware.
- Listen on a cold start. A brief rattle on start-up often points me toward chain tension, guides, or a cam phaser. Silence does not clear the engine, but noise makes mechanical timing much more suspicious.
- Inspect connectors and wiring. Cam and crank sensors live in a harsh environment. Heat, oil, and vibration can damage the connector pins or harness insulation, and that is cheap to miss if you only scan codes.
- Compare live data. I want to see commanded cam position versus actual cam position if the scan tool can read it. Large or unstable differences tell me whether the ECU is fighting a timing problem or just reacting to bad input.
- Move to mechanical checks if the data points that way. If the earlier checks suggest a real timing issue, I verify timing marks at top dead centre, inspect belt or chain condition, look at tensioner travel, and check the phaser against workshop data. An oscilloscope can help on stubborn sensor cases, but it is not my first move.
The point of this sequence is simple: I want to prove whether the engine is genuinely out of time before I authorise a timing job. If the live data and mechanical checks disagree, I keep digging instead of guessing.
What repairs usually cost in the UK
There is a big gap between a cheap electrical fault and a true timing repair, which is why diagnosis matters so much. Recent UK pricing from RAC puts timing chain replacement around £750 to £1,000, while BookMyGarage shows diagnostic checks ranging from roughly £20 to £159 depending on the garage and the scope of the test.
| Repair path | Typical UK cost | What it usually means |
|---|---|---|
| Initial diagnostic check | About £50 to £100, sometimes less or more depending on the garage | Fault-code reading, live data, and basic checks |
| Sensor or wiring repair | About £80 to £250 | Bad sensor, damaged connector, or harness fault |
| VVT solenoid or phaser work | About £150 to £500 | Oil control or cam timing movement problem |
| Timing chain repair | About £750 to £1,000+ | Worn chain, guides, tensioner, or timing misalignment |
| Timing belt related repair | Varies widely by engine | Jumped belt, bad tensioner, or incorrect timing setup |
Small electrical jobs can be reasonable, but once the fault reaches the chain, belt, or phaser, labour becomes the expensive part. That is why I always want the diagnosis to separate a replaceable part from a deeper timing issue before anyone approves the work.
What I check before spending money on parts
If I were standing at the car with this fault on the scanner, these are the checks I would want answered before approving expensive parts:
- Has the oil been serviced on time, and is the correct grade actually in the engine?
- Did the code appear after a recent timing belt, chain, sensor, or head repair?
- Is there cold-start rattle, or is the engine quiet enough to suggest an electrical issue first?
- Do related codes point to misfires, oil pressure, or another cam position fault?
- Does the code return immediately after clearing, or only after a drive cycle?
- Do live cam/crank readings match the mechanical timing marks?
If the answer is yes to oil neglect, rattle, or a recent timing job, I get much less interested in swapping sensors first and much more interested in the actual timing hardware. If the engine runs smoothly and the code is intermittent, I start with the cheap checks, because that is where the wasted money usually hides.
The best way to handle this fault is to treat it as a timing question first and a parts question second. That keeps you from replacing sensors that were only reporting the real problem, and it also helps you judge when the car is safe enough for a short trip to the garage and when it should be recovered instead. If the engine is quiet and the fault is intermittent, start with oil, wiring, and live data; if it rattles or misfires, assume the problem is mechanical until proven otherwise.
