If you’re working on a Cummins ISX15 and run into fault code 0731 (camshaft and crankshaft misalignment) after an overhaul, it can be frustrating.
Especially when:
- The engine runs smooth
- Timing appears correct
- The crank pins correctly
- The cam wedges properly
- Sensors and tone wheel check out
👉 Yet the code is still active.
What Code 0731 Actually Means
Fault code 0731 indicates that the ECM is detecting a timing mismatch between the crankshaft and camshaft signals.
The ECM compares:
- Crankshaft position sensor data
- Camshaft position sensor data
If the relationship between those signals is off – even slightly – it will trigger a fault.
👉 Code 0731 is based on camshaft and crankshaft signal correlation – not just mechanical timing – so the engine can be physically in time and still trigger a fault.
Why This Happens After an Overhaul
After a rebuild, everything has been:
- Disassembled
- Reinstalled
- Torqued in sequence
Even when timing appears correct, small mechanical shifts can occur during assembly.
On ISX15 platforms, the ECM is sensitive enough that even very small camshaft movement during assembly can trigger a correlation fault.
That’s where this issue shows up, as cumulative gear train tolerances can slightly shift cam-to-crank relationship even when all timing components are installed correctly.
The Overlooked Cause: Cam Movement During Rocker Installation
This is where many correctly timed engines still end up setting code 0731. One of the most common (and least obvious) causes is:
👉 Camshaft movement during rocker arm installation
Here’s what happens:
- Cam gear is installed and torqued
- Timing wedge is removed
- Rocker assemblies are installed and torqued
During this process:
👉 The force from torquing the rocker assemblies can slightly rotate the camshaft if it is not fully secured. This alone is enough to change cam/crank correlation. Even a small movement is enough to:
- Change cam/crank correlation
- Trigger code 0731
- Cause a persistent timing fault
Why the Engine Can Still Run Fine
This is what makes the issue confusing.
The engine may:
- Start normally
- Idle smoothly
- Run without noticeable performance issues
But the ECM is detecting a precision timing variance, not a major mechanical failure.
👉 Modern engines are sensitive enough that even when the engine pins correctly at TDC, a slight signal offset can fall outside the ECM’s acceptable timing range and trigger a code.
How to Fix ISX15 Code 0731 (Correct Procedure)
If you’ve verified:
- Crank pins correctly
- Cam wedges correctly
- Tone wheel is intact
- Sensors are working
Then focus on the install process.
Correct Fix
- Remove rocker assemblies
- Reinstall cam gear
- Install and torque cam gear with the timing wedge still in place
- Install rocker assemblies while the wedge is still installed
- Only remove the wedge after all components are torqued
👉 This prevents the camshaft from shifting during assembly.
This is the difference between a correctly timed engine and one that continues to set a correlation fault.
Why This Fix Works
The timing wedge locks the camshaft in the correct position.
If removed too early:
- The camshaft is free to move slightly
- Rocker torque can rotate the cam
- Timing relationship changes
By keeping the wedge installed:
👉 You maintain correct alignment throughout the entire process.
Other Possible Causes to Rule Out
The tone wheel must remain correctly indexed to the crankshaft, as even slight movement can send an incorrect position signal without affecting mechanical timing.
If the issue persists, check:
- Damaged or misaligned tone wheel
- Faulty cam or crank sensors
- Wiring issues or signal interference
- Incorrect gear installation
- Excessive backlash in timing components
But in many overhaul cases:
👉 The issue usually comes down to installation sequence – not component failure.
Common Mistake to Avoid
One of the biggest mistakes is assuming:
👉 “If it pins and wedges correctly, it must be right”
That’s not always true.
The order of installation and when components are torqued matters just as much as alignment.
Final Takeaway
ISX15 code 0731 after an overhaul is often not a sensor issue or a bad part.
👉 It’s a timing relationship issue introduced during assembly.
Specifically:
- Camshaft movement after wedge removal
- Rocker installation shifting the cam
Fixing it requires:
- Reinstalling components in the correct sequence
- Keeping the cam locked during torque procedures
Need Help Diagnosing a Timing or Rebuild Issue?
If you’re dealing with:
- Timing-related fault codes
- Post-overhaul issues
- Repeat failures
At Highway and Heavy Parts, we help you identify the problem and get the right parts the first time.
Call 844-304-7688 or visit highwayandheavyparts.com to place your order today.
From diagnosis through delivery, we’re Highway and Heavy Parts.
