P0340 & P0341 Codes: Camshaft Position Sensor Circuit (GM Guide)

P0340 and P0341 both concern the camshaft position sensor circuit — the signal that tells the module which cylinder is on compression and which is on exhaust. Without it, the engine does not know when to inject fuel or fire a plug. On 2014–2019 GM trucks, GM has published multiple bulletins pointing at one specific connector — X154 — for chafing and corrosion, and that is where to look before buying a sensor. This is also one of the few codes where "safe to drive" is the wrong answer: losing this signal can leave you cranking and not starting, or stalling in traffic.

What Do P0340 and P0341 Mean?

The camshaft carries a reluctor wheel with a deliberately uneven tooth pattern — narrow and wide slots. As it turns, the camshaft position sensor detects the changing magnetic flux and produces a digital on/off signal whose frequency tracks camshaft speed.

The uneven pattern is the clever part. By recognising the narrow and wide teeth, the module can work out not just how fast the camshaft is turning but exactly where it is — which tells it which cylinder is on its compression stroke and which is on exhaust. That determines injection timing and spark sequence.

The module also produces a replicated camshaft signal output that other modules use to monitor engine speed, which is why a fault here can produce complaints in places that seem unrelated.

GM's setting condition for P0340 is specific: the code sets when the module does not receive a signal from the camshaft position sensor across roughly 200 engine revolutions. That is not a momentary glitch — it is a sustained absence.

P0340 vs P0341 — the Distinction Worth Knowing

These two get treated as interchangeable and they are not.

Code	What it says	Where it points
P0340 — Camshaft Position Sensor Circuit	The module is not receiving a signal	Opens, shorts, a disconnected sensor, a dead sensor, a total supply failure
P0341 — Camshaft Position Sensor Circuit Range/Performance	A signal is present but wrong — erratic, or outside the expected pattern	Marginal connections, a damaged reluctor wheel, a chafed wire, timing that has drifted

The practical difference: P0340 sends you looking for something that is disconnected or dead. P0341 sends you looking for something that is partly working — a corroded pin still passing signal but not cleanly, a wire chafed nearly through, a reluctor with a damaged tooth.

Seeing both together is common and informative. It usually means a connection that is intermittently failing rather than one that has failed outright — which is exactly what the GM bulletins on these codes describe.

The X154 Connector — Where GM Says to Look

This is the most actionable thing on the page, and it applies to a very large number of trucks.

On 2014–2019 Silverado and Sierra with the 5.3L and 6.2L V8s, GM has addressed these codes across several preliminary information documents — reported as PIP5335D, PIP5553A and PIP5724 — and they converge on the same area: the wiring at the front of the engine, and specifically the X154 connector on the lower left side of the engine front cover.

Two distinct failure modes are documented there:

• Chafing. A wiring jumper harness rubs against the bolt for the X154 connector until the insulation wears through. A specific bolt, on a specific bracket, wearing through a specific harness.
• Corrosion inside the X154 connector from water intrusion. The signal degrades rather than disappearing, which fits P0341 particularly well.

Why this matters so much: a camshaft position sensor is an inexpensive part, and it is the obvious thing to replace. But if the fault is a chafed wire or a corroded connector, the new sensor changes nothing — and you have paid for a part and the labour to fit it, sometimes in an awkward location.

GM's repair for the corroded connector is not the whole harness either. A connector pigtail — reported as part 84941154 — allows a clean connector to be spliced in. That is a considerably smaller job than it first appears.

If you have a 2014–2019 GM truck with either of these codes, inspect the front-of-engine wiring and the X154 connector before ordering anything. Look for a rub mark where the harness passes the connector bolt, and pull the connector apart to look for green deposits and moisture.

These bulletins are corroborated from technician-facing sources rather than documents we opened. The connector identification is consistent enough across them to be worth acting on — but ask a dealer to check current bulletins against your VIN.

Why This One Is Urgent

Most sensor codes on this site come with a "generally safe to drive" note. This is not one of them, and the reason is mechanical rather than cautious.

Without a camshaft signal, the module cannot tell which cylinder is on compression. It therefore cannot sequence the injectors correctly. On many engines the fail-safe response is to disable fuel injection entirely — the engine cranks and cranks and will not fire.

The failure modes owners report follow directly from that:

• Extended cranking before the engine catches — often the first warning, and it strains the battery and starter.
• No-start, frequently when the engine is warm, which is the signature of a marginal connection expanding with heat.
• Stalling without warning, including at low speed while turning.
• Reduced engine power mode.

A stall in traffic is a genuine hazard — you lose power steering assist and brake booster assist at the same moment. And a vehicle that will not restart leaves you wherever it stopped.

So the honest answer: if you have had extended cranking or a stall, deal with this now rather than at the next service. An intermittent camshaft signal fault does not stay intermittent.

If P0016 Is Stored Alongside, the Picture Changes

This is the branch point that separates a cheap repair from an expensive one.

P0016 is the crankshaft-camshaft correlation code. It means the two signals are out of the expected relationship with each other — not that one is missing, but that they disagree about where the engine is.

The distinction matters enormously:

• P0340 or P0341 alone points at the sensor and its circuit. Inspect the wiring, check the connector, test the sensor.
• P0340 or P0341 with P0016, particularly after the sensor and wiring have been verified good, points at mechanical timing — a stretched timing chain, a worn tensioner, or a damaged or slipped reluctor wheel.

Supporting evidence for the mechanical case: a rattle from the front of the engine, especially on cold start, is the classic timing chain symptom. So is a history of extended oil change intervals or oil consumption, since chain wear tracks oil condition closely.

Our P0016 guide covers that code in detail, and the P0014 guide covers the variable valve timing side, which shares the same sensors and the same oil dependency.

Access Changes the Bill More Than the Part Does

A camshaft position sensor is generally an inexpensive component. Where it sits is what determines the cost of fitting it.

Application	Reported sensor	Access note
5.3L L83 (2014–2019 trucks)	12684186	Front of engine — the same area as the X154 wiring
6.0L Vortec L96	12591720	Behind the water pump. Access is difficult and the labour is significant
6.6L Duramax LML	12672642	Reported as a common failure point on this engine

The 6.0L is the one to be aware of. A sensor that costs very little sits behind a water pump, which turns a nominally trivial part into a real job. That is another argument for confirming the diagnosis properly before starting — and for replacing the connector or repairing the harness if that is the actual fault, since you will not want to go back in.

Part numbers vary by engine and model year, so confirm against your VIN rather than a number from an article. And on a sensor whose signal quality is the whole point, fitting a quality part matters — a marginal aftermarket sensor produces exactly the erratic signal P0341 describes.

A Note on Sourcing for This Code

We cite documents we have read and label the rest.

The GM preliminary information documents referenced here — PIP5335D, PIP5553A and PIP5724 — are corroborated from technician-facing sources rather than opened by us. What gives them weight is consistency: multiple independent references identify the same connector, the same bolt, and the same two failure modes on the same platform. That is a stronger pattern than a single unverified claim.

The setting condition, the reluctor wheel description and the sensor's role are consistently reported by technicians working from GM service information.

Part numbers quoted here are reported rather than confirmed by us against GM's catalogue. Order against your VIN.

Have a dealer check your VIN against current bulletins — that is free and definitive in a way no article is, and on a code with this many platform-specific documents it is genuinely worth doing.

Symptoms of P0340 and P0341

• Check engine light on
• Extended cranking before the engine starts — often the earliest sign
• No-start, particularly when warm
• Stalling without warning, including at low speed
• Reduced engine power message
• Rough running, hesitation or misfiring
• Poor fuel economy
• Rattle from the front of the engine, where timing is involved

On urgency: high. Extended cranking is the fault warning you before it strands you. A warm no-start pattern is a marginal connection announcing itself. And a stall at speed is a safety issue in its own right. This is not a code to carry for months.

Causes and How to Confirm Each

Cause	How to confirm it	Notes
Harness chafing at the X154 connector bolt	Inspect the front-of-engine wiring for a rub mark where it passes the connector bolt	GM-documented on 2014–2019 trucks. Check before buying a sensor
Corrosion inside the X154 connector	Separate the connector and look for green deposits and moisture	Repairable with a pigtail rather than a full harness
Failed camshaft position sensor	After the wiring is cleared. Check for 5 V reference, good ground and signal at the connector	Common, but second to wiring on these platforms
Poor connection elsewhere at the front of the engine	Inspect nearby connectors — X159 and others in that area are reported	Explains odd companion codes appearing together
Stretched timing chain or worn tensioner	P0016 alongside, plus a front-of-engine rattle on cold start	The expensive branch. Verify the sensor and wiring first
Damaged or slipped reluctor wheel	Erratic signal with good wiring and a good sensor. Usually needs access to inspect	Fits P0341 better than P0340
Oil condition affecting VVT components	Check oil level, condition and service history	Cam timing systems run on oil pressure — see our P0014 guide
Poor-quality aftermarket sensor	Establish what was fitted, especially if the code returned quickly	Signal quality is the whole function here
ECM fault	Last, after wiring, sensor and mechanical timing are excluded	Rare relative to everything above

How Are P0340 and P0341 Diagnosed?

1. Record all codes. P0016 alongside is the single most important thing to note — it moves the diagnosis toward mechanical timing.
2. Note whether it is P0340, P0341, or both. No signal versus a bad signal point at different faults.
3. Inspect the front-of-engine wiring and the X154 connector for chafing at the connector bolt and corrosion inside the connector. This is the documented cause on 2014–2019 trucks and it costs nothing to look.
4. Check nearby connectors in the same area while you are there.
5. Test the sensor circuit at the connector with the key on — 5 V reference, ground, and signal.
6. Check oil level and condition, since cam timing components depend on it.
7. Listen for a rattle on cold start, which supports the timing chain case.
8. Repair wiring or connector faults before replacing the sensor — a pigtail may be all that is needed.
9. Replace the sensor with a quality part if the circuit tests good, matched to your VIN.
10. If codes persist with good wiring and a good sensor — particularly with P0016 — investigate timing rather than continuing to replace electrical parts.

Parts and Cost

Repair	What it involves	Cost picture
Harness repair at the chafe point	Repair the damaged wire and reroute it clear of the connector bolt	The cheapest real fix. And it prevents the repeat
Connector pigtail	Splice in a clean connector where X154 is corroded — reported as part 84941154	Modest — far less than a harness
Camshaft position sensor (accessible)	Front-of-engine applications	Inexpensive part, short job
Camshaft position sensor (6.0L, behind the water pump)	Same inexpensive part, much harder access	Labour dominates. Get the diagnosis right first
Oil and filter service	Where oil condition is a factor in the timing system	Modest, and worth doing regardless
Timing chain and tensioner	Where P0016 and a rattle confirm mechanical timing wear	The large one. Make the evidence earn it
Sensor replaced while a chafed wire remains	What happens when the harness is not inspected	Part and labour spent, fault still present

Confirm all part numbers against your VIN. Sensors differ between the 5.3L, 6.0L and Duramax applications, and they are not interchangeable.

What Other P0340 / P0341 Pages Get Wrong

• Leading with the sensor. On 2014–2019 GM trucks, GM's own documents point at harness chafing and connector corrosion at X154. A new sensor does nothing for either, and on some engines the access alone makes that an expensive mistake.
• Never naming the connector. X154, on the lower left side of the engine front cover, with the harness chafing on its mounting bolt. That converts a vague "check the wiring" into a specific place to look.
• Treating P0340 and P0341 as the same code. One means no signal, the other means a bad signal. Opens and dead sensors versus corroded pins and damaged reluctors — different searches.
• Ignoring P0016. With the sensor and wiring verified, P0016 alongside moves this from an electrical repair to a timing chain investigation. That is the difference between a pigtail and a major job.
• Calling it safe to drive. Without a cam signal many engines disable fuel injection outright — cranks but will not fire. Extended cranking, warm no-starts and unannounced stalls are all documented. This deserves more urgency than a typical sensor code.
• Not mentioning access. The same cheap sensor sits at the front of the engine on one application and behind the water pump on another. That changes the quote entirely.
• Suggesting a cheap sensor is fine. This component's entire job is producing a clean, precisely patterned signal. A marginal part reproduces exactly the erratic signal P0341 describes.

Frequently Asked Questions

Do I need a new camshaft position sensor?

Check the wiring first, especially on a 2014–2019 GM truck. GM's documents on these codes point at a harness chafing on the X154 connector bolt at the lower left of the engine front cover, and at corrosion inside that connector. Both produce these codes with a perfectly good sensor, and the corroded connector can often be fixed with a pigtail.

What's the difference between P0340 and P0341?

P0340 means the module is receiving no signal at all — think opens, disconnections, a dead sensor. P0341 means a signal is present but wrong: erratic or outside the expected pattern, which fits a corroded pin, a nearly-chafed wire, or a damaged reluctor wheel. Seeing both usually means an intermittent connection.

Can I drive with this code?

We would not recommend it if you have had extended cranking or a stall. Without a camshaft signal the module cannot sequence the injectors, and many engines respond by disabling fuel injection — the engine cranks and will not fire. Stalling at speed also costs you power steering and brake assist.

Why does it start fine cold but not when warm?

That pattern fits a marginal connection. Metal expands with heat, a corroded or partly chafed connection loses contact, and everything works again once it cools. Mention it specifically when the vehicle is diagnosed — it points at the connector rather than the sensor.

I have P0016 as well. Does that change anything?

Significantly. P0016 means the crankshaft and camshaft signals disagree about where the engine is. With the sensor and wiring already verified good, that points at mechanical timing — a stretched chain, a worn tensioner, or a damaged reluctor wheel — rather than an electrical fault. A rattle from the front of the engine on cold start supports that.

How much is the sensor?

The part is generally inexpensive. What varies enormously is access: on some engines it is at the front and straightforward, while on the 6.0L it sits behind the water pump and the labour dominates the bill. That is a good reason to confirm the diagnosis before starting.

Can a timing chain cause P0341?

Yes. A stretched chain lets the camshaft drift out of its expected relationship with the crankshaft, which produces a signal that is present but not where the module expects it. That is why P0016 alongside is such an important clue, and why a front-of-engine rattle is worth reporting.

Is an aftermarket sensor acceptable?

Quality matters more here than on many parts. The sensor's whole function is producing a clean signal with a precise tooth pattern, and a marginal one generates exactly the erratic output that sets P0341. If you are going into a difficult location to fit it, it is a poor place to save a small amount.

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