What is the difference between P0016 and P0017?

Both compare a camshaft's position against the crankshaft's, but they use different camshaft sensors on the same bank. P0016 is measured against sensor A, which on a twin-cam engine is normally the intake camshaft; P0017 is measured against sensor B, normally the exhaust camshaft. Which of them is stored tells you where to look. Both together mean both camshafts have shifted relative to the crank, so the shared timing chain or belt is the suspect. P0017 alone means only the exhaust side has moved, which points at that camshaft's phaser, the short chain between the two camshafts if the engine has one, or the exhaust camshaft sensor.

Does P0017 always mean a stretched timing chain?

No, though a chain is always on the list and must be ruled out. P0017 stored on its own, without P0016 beside it, is more often the exhaust camshaft phaser, a loose phaser centre bolt, a secondary chain between the camshafts, or a faulty exhaust camshaft sensor. The stretched chain scenario usually sets both correlation codes together, because a slack primary chain moves both camshafts at once. A rattle for the first seconds after a cold start is the sign that pushes it back towards the chain.

Can I drive with a P0017 code?

As far as a garage, and no further. Any correlation code raises the possibility that the timing drive has moved, and on an interference engine a chain or belt that jumps puts valves into pistons. If the engine rattles at start-up, is hard to start, or has gone into limp mode, have it recovered rather than driven.

Will P0017 fail an MOT?

Yes. The illuminated engine management lamp is a major defect for petrol cars first used on or after 1 July 2003 and diesels from 1 July 2008, and that defect records 371,859 failures in the DVSA data behind this site. A car that has dropped into limp mode may also be unable to reach the fast idle speed the emissions test requires, which fails it a second time as an incomplete emissions check.

Powertrain code · standard

P0017Exhaust camshaft out of step with the crankshaft, bank 1

Standard definition: Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)

Last updated 27 July 2026

Quick answer

The same correlation check as P0016, but made against the second camshaft sensor on bank one, which on a twin-cam engine is normally the exhaust camshaft. Where P0016 on its own implicates the whole timing drive, P0017 on its own points more narrowly at the exhaust side of it.

How the car works this out

The control unit holds a second reference for the exhaust camshaft and checks it against the crankshaft in exactly the same way, allowing for whatever the exhaust phaser has been commanded to do. Which codes are stored together is the diagnostic information. If P0016 and P0017 appear at once, both camshafts have moved relative to the crank, which means the drive they share — the main chain or belt — is what has changed. If P0017 appears alone, the intake camshaft is still where it should be and only the exhaust side has moved, which shifts suspicion to that camshaft's phaser, its centre bolt, the short chain running between the two camshafts on the engines that use one, or the exhaust camshaft sensor itself.

What you might notice

A rattle at cold start, if the cause is a chain or tensioner
Rough idle, reduced power or limp mode
Extended cranking before the engine starts
The engine management lamp on, often with a variable valve timing code such as P0014 stored alongside

What causes it

Most likely first. A code names the check that failed, not the part that failed it, so more than one of these can produce the same number.

1A worn exhaust camshaft phaser, or a phaser centre bolt that has loosenedCommon
2A stretched primary chain or slipped belt, particularly if P0016 is stored alongsideCommon
How to check: Check whether P0016 is present. Both codes together move the diagnosis to the main timing drive; P0017 alone keeps it on the exhaust side.
3A stretched or slack secondary chain between the intake and exhaust camshafts, on the engines built that wayPossible
4A failing exhaust camshaft position sensor or a damaged trigger wheel on that camshaftPossible
How to check: Compare the live signal against the crankshaft signal on a scope if a garage has one. It is the cheap end of the possibilities and worth eliminating first.
5On engines where the high-pressure fuel pump runs off this camshaft, a badly worn follower or cam lobeLess common
How to check: Fuel pressure codes stored alongside make this worth inspecting. Follower wear on those engines is a known failure and it damages the camshaft if left.
6Low oil pressure preventing the chain tensioner from taking up slackLess common

What to do about it

1Read the full code list before anything else. P0017 alone and P0017 with P0016 are two different jobs.
2Listen for a rattle at cold start, and stop using the car if there is one.
3Have the exhaust camshaft sensor and its trigger wheel checked before opening the front of the engine. It is the least expensive possibility and it does happen.
4If the engine drives its fuel pump from this camshaft, have the follower inspected while the cam cover is off. It is a small job at that point and an engine-damaging one if it is left.

Can you keep driving?

Only to a garage

A correlation code always carries the possibility that the timing drive has moved, and that possibility is why this is not a code to live with. It is marginally less alarming than P0016 alone, because an exhaust-side-only error is more often a phaser or a sensor than a chain, but the downside is the same engine. Drive it to a garage and no further, and if there is a rattle from the timing drive, have it recovered instead.

Will it fail an MOT?

The lamp is the immediate problem: a major defect on petrol cars first used from 1 July 2003 and diesels from 1 July 2008. Worth knowing before you book the test is that this code is rarely a quick fix, so there is little point in gambling on clearing it beforehand. Wiping the code resets the readiness monitors as well, the tester can see they have not completed, and the emissions check on many cars cannot be finished until they have run. You end up failing on an incomplete emissions test with the underlying timing fault still there.

The light this turns on

Engine management lightThe engine management system has found a fault it cannot correct and has stored a code for it. The car will usually still drive, but an illuminated engine light is an automatic MOT failure on petrol cars first used from 1 July 2003 and diesels from 1 July 2008.

Common questions

What is the difference between P0016 and P0017?: Both compare a camshaft's position against the crankshaft's, but they use different camshaft sensors on the same bank. P0016 is measured against sensor A, which on a twin-cam engine is normally the intake camshaft; P0017 is measured against sensor B, normally the exhaust camshaft. Which of them is stored tells you where to look. Both together mean both camshafts have shifted relative to the crank, so the shared timing chain or belt is the suspect. P0017 alone means only the exhaust side has moved, which points at that camshaft's phaser, the short chain between the two camshafts if the engine has one, or the exhaust camshaft sensor.
Does P0017 always mean a stretched timing chain?: No, though a chain is always on the list and must be ruled out. P0017 stored on its own, without P0016 beside it, is more often the exhaust camshaft phaser, a loose phaser centre bolt, a secondary chain between the camshafts, or a faulty exhaust camshaft sensor. The stretched chain scenario usually sets both correlation codes together, because a slack primary chain moves both camshafts at once. A rattle for the first seconds after a cold start is the sign that pushes it back towards the chain.
Can I drive with a P0017 code?: As far as a garage, and no further. Any correlation code raises the possibility that the timing drive has moved, and on an interference engine a chain or belt that jumps puts valves into pistons. If the engine rattles at start-up, is hard to start, or has gone into limp mode, have it recovered rather than driven.
Will P0017 fail an MOT?: Yes. The illuminated engine management lamp is a major defect for petrol cars first used on or after 1 July 2003 and diesels from 1 July 2008, and that defect records 371,859 failures in the DVSA data behind this site. A car that has dropped into limp mode may also be unable to reach the fast idle speed the emissions test requires, which fails it a second time as an incomplete emissions check.

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