A stretched or rattling timing chain is a well-known failure pattern on BMW. The diesels hit hardest are the N47 and N57, along with the gasoline N20; the B58 shows the problem less often. The engine control unit (DME) doesn’t detect the problem directly—it infers it from crankshaft-to-camshaft correlation codes and VANOS codes: P0016, P0011, P0014, 2A82, 2A87.
The telltale sign is a short, sharp rattle right after a cold start. Don’t ignore it: the chain snaps, the valves meet the pistons, and the engine takes severe damage. On the N47, a snapped chain remains the number-one failure that leaves the car not worth repairing.
Which Engines Are Affected
| Engine | Type | Notes |
|---|---|---|
| N47 | diesel | pre-LCI versions hit hardest; a snapped chain makes the car economically unrepairable |
| N57 | diesel | chain rattle, knock from the rear of the timing cover |
| N20 | gasoline | tensioner wear typically after 50,000–75,000 miles |
| B58 | gasoline | isolated cases |
How the DME Detects the Problem
Chain length isn’t measured directly. The DME registers a mismatch between crankshaft and camshaft positions and throws correlation codes. VANOS codes show up on top of that.
That leads to one important consequence: the code points to a symptom, not the cause. Behind a correlation code could be a stretched chain, a worn tensioner, or a faulty VANOS unit—you have to dig further.
Symptoms
- A rattle for 1–3 seconds after a cold start
- Check Engine light with correlation codes
- Limp mode when the load changes
- On the N47/N57, a knock from the rear of the timing cover
Causes
- Chain stretch. On the N47, pre-LCI engines are especially susceptible.
- Worn tensioner. Typical on the N20 after 50,000–75,000 miles.
- VANOS unit. Can be mechanically faulty or hydraulically too slow.
- Late oil changes. Oil sludge clogs the tensioner and keeps it from working.
Cluster Error Codes
| Code | Meaning |
|---|---|
| P0016 | Crankshaft/camshaft correlation fault |
| P0011 | Intake camshaft phase deviation |
| P0014 | Exhaust camshaft phase deviation |
| 2A82 | VANOS code |
| 2A87 | VANOS code |
⚠️ The source material claims the cluster is “8 codes” with individual explainer pages, but only five are listed. The full set of eight is not confirmed in this material.
Diagnosis
The DME only sees the problem indirectly. The decisive trigger for a check is a rattle right after a cold start—if it happens every time or recurs several times a week—or a stored P0016 / P0011 code.
On the N47, that suspicion calls for a borescope inspection of the chain. It’s the only way to assess its condition without disassembly.
Repair and Chain Replacement
Once the failure is confirmed, the chain gets replaced. On most of these engines the motor has to be dropped to get at it, which drives up labor significantly.
Cost depends on the shop and on how accessible the assembly is. In relative terms, the cost picture looks like this:
| Engine | Relative Replacement Cost |
|---|---|
| N20 | moderate |
| B58 | high |
| N47 | high |
What Shops See in Practice
- Pre-LCI N47s show up for diagnosis noticeably more often than later versions.
- On the N20, the tensioner often wears out within 50,000–75,000 miles.
- Late oil changes speed up the failure: oil sludge blocks the tensioner.
- With a confirmed snapped chain on the N47, repair is often no longer economically worthwhile.
FAQ
How do you know it’s time to replace the chain?
The trigger is a rattle right after a cold start—if it happens every time or recurs several times a week—or a stored P0016 / P0011. On the N47, that calls for a borescope inspection of the chain.
Why does a correlation code appear before the knock?
The DME registers the phase mismatch before the wear becomes audible. As long as the VANOS system can still compensate for the deviation, there may be no external symptoms.
The Bottom Line
A stretched or rattling timing chain is a predictable failure on the N47, N57, N20, and some B58 engines—not a fluke. The DME catches it indirectly, through correlation and VANOS codes, so the code alone doesn’t name the cause. The one reliable move: with a rattle after a cold start or a stored P0016 / P0011, don’t put off the borescope inspection—on the N47, “too late” almost always means an engine that’s economically unrepairable.