P25E4: B Camshaft Position - Unable to Achieve Locked Position Bank 1

What it means

Camshaft phaser B on bank 1 cannot reach its base position at engine shutdown so the lock pin never engages. Next cold start may run rough until oil pressure builds.

At a glance

• Usually lights the check-engine light

How it works

Camshaft phaser B on bank 1 must return to its base angle so its lock pin can hold it in position when the engine is off. The control module detects that the phaser does not reach that locked position, which can leave cam timing unsettled at the next start.

Common causes

Most likely first.

1. Worn vanes or housing inside the phaser
2. Sludge or contaminated oil prevents return to base
3. Oil control valve leaks internally

Symptoms

• Check engine light on
• Power loss especially in mid-rpm range
• Possible rough idle or stalling
• Increased fuel consumption

How to diagnose it

1. Review freeze-frame data and live commanded versus actual cam angle for phaser B on bank 1, noting whether it fails to return to base before shutdown.
2. Check whether rough running is most pronounced on a cold start and improves as oil pressure builds, which can support a failure to lock at shutdown.
3. Check engine oil level, condition, and specified viscosity; inspect for sludge that could impede return of the bank 1 phaser B.
4. Inspect the bank 1 phaser B oil control valve and its wiring, then check whether the valve leaks internally or fails to direct oil correctly.
5. Test the phaser's return and lock function and inspect its internal wear using the manufacturer's procedures.

Common fixes

• Correct the oil level and replace contaminated or incorrect-viscosity oil and filter.
• Clean restricted oil passages or replace a leaking bank 1 phaser B oil control valve.
• Repair damaged wiring or connector terminals for the bank 1 phaser B valve.
• Replace a worn bank 1 phaser B that cannot return to or hold its base position.

Can I keep driving?

You may be able to drive gently if the engine settles after starting, but expect rough running or stalling until oil pressure builds and avoid demanding acceleration. If it continues to run roughly or stalls, stop driving because poor cam timing can impair control and worsen engine wear.