P0344 on the 6.6L Duramax LMM is a camshaft position (CMP) sensor A circuit intermittent fault. The CMP sensor reads a target on the camshaft so the ECM can synchronize injection timing. P0344 specifically flags an intermittent signal, meaning the sensor works most of the time but drops out momentarily, which can cause brief stumbles, stalling, or occasional hard starts.
Intermittent faults are among the more frustrating to chase because the problem may not be present when you look. On the LMM the cam signal is important for timing, so even a brief dropout can cause a noticeable stumble or a no-start attempt. The key to P0344 is catching the fault in the act with live data and a wiggle test, since the cause is usually a loose connection or a marginal sensor rather than a total failure.
What P0344 means
P0344 is the intermittent version of a camshaft sensor circuit fault. The ECM receives a valid cam signal but sees it cut out briefly and return. This differs from a hard circuit code because the signal is present most of the time. The cause is typically a loose or corroded connection, a marginal sensor, or a wiring problem that only acts up with heat or vibration.
Common causes
- Loose, corroded, or backed-out sensor connector
- Marginal or heat-sensitive camshaft position sensor
- Chafed or intermittently shorting wiring
- Vibration-related connection dropouts
- Debris intermittently affecting the signal
Symptoms
- Occasional stumble, hesitation, or stall
- Intermittent hard start or extended crank
- Check engine light with P0344 stored
- Symptoms that come and go with heat or rough roads
- Possible correlation codes with the crank sensor
How to diagnose it
Because the fault is intermittent, try to catch it in the act. With a scan tool monitoring the cam signal or engine RPM, perform a wiggle test on the sensor connector and harness, watching for dropouts. Inspect the connector for corrosion, spread pins, and a loose lock. Consider whether the fault appears when the engine is hot, which can indicate a heat-sensitive sensor. Check the wiring for chafing points and confirm continuity back to the ECM. Clean the sensor tip and confirm the target is intact.
How to fix it
Repair the connection first, cleaning corroded pins, reseating the connector, and fixing any chafed wiring, since a loose connection is the most common cause of an intermittent cam code. If the connection is solid but the fault recurs, especially when hot, replace the camshaft position sensor. After the repair, clear the code, monitor the cam signal through a heat cycle and a road test, and confirm the dropout is gone. For the correct CMP sensor for your LMM Duramax, contact sales@coredieselparts.com.
Frequently asked questions
Why is P0344 so hard to diagnose?
It is intermittent, so the fault may not be present during inspection. Catching it with a wiggle test while monitoring live data is the most reliable approach.
Can heat cause P0344?
Yes. A marginal sensor can drop out only when hot, and a loose connection can expand and lose contact with heat. Test through a full warm-up if the fault is heat related.
Is it safe to drive with P0344?
Drive with caution. Intermittent stalling or stumbling can be dangerous, and the fault may worsen. Repair the connection or sensor promptly.
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