Here are some of the most likely culprits:
* Low Oil Level: This seems obvious, but it's the first thing to check. Check your oil level with the dipstick *after* the engine has been off for a while to allow the oil to settle. Low oil will lead to low pressure.
* Oil Pump Failure: The oil pump is responsible for circulating oil. Failure of the pump itself (mechanical failure, worn gears, etc.) is a major suspect. This is a costly repair.
* Clogged Oil Pick-Up Tube: The oil pump draws oil from the bottom of the oil pan through the pick-up tube. If this tube becomes clogged with sludge or debris, the pump can't get enough oil.
* Worn or Damaged Main Bearings: These bearings support the crankshaft. If they're worn or damaged, oil can leak past them, reducing pressure. This is a significant engine repair.
* Worn Connecting Rod Bearings: Similar to main bearings, worn connecting rod bearings will allow oil to escape, resulting in low pressure. This is also a significant engine repair.
* Oil Cooler Issues: A leak in the oil cooler will cause oil loss and low pressure. This is especially likely if the pressure drops when the engine reaches operating temperature.
* Blocked Oil Filter: Although less likely to cause a complete pressure drop to zero, a severely clogged oil filter can restrict oil flow.
* Sensor Failure (Oil Pressure Sensor): While less likely to be the root cause, a faulty oil pressure sensor could give a false reading of zero pressure even if there's sufficient oil pressure. However, other symptoms (like engine knocking) would likely accompany bearing wear or oil pump failure.
Troubleshooting Steps (in order):
1. Check the Oil Level: This is the absolute first thing to do.
2. Check the Oil Filter: Make sure it's not overly tight and is not excessively blocked.
3. Visual Inspection: Look for any obvious oil leaks around the engine, oil pan, oil cooler, and oil filter.
4. Professional Diagnosis: This is crucial. Take your truck to a qualified mechanic specializing in diesel engines, particularly Cummins engines. They can use diagnostic tools to assess oil pressure accurately and pinpoint the problem.
Ignoring this problem will likely lead to a very expensive engine rebuild or replacement. Get it checked out immediately.
