A persistent “Engine Intake Manifold 1 Pressure” fault code can be a frustrating issue for truck drivers. This article details a real-world troubleshooting experience with this code on a 2017 Cummins ISX15 engine, offering valuable insights for those facing similar problems. The initial symptom was a 25% engine derate, accompanied by the “125 intake manifold pressure” message on the dash, but without a check engine light. The message would disappear after about two hours.
Initial troubleshooting focused on identifying potential air leaks in the intake manifold system. Visual inspections and pressure testing were conducted, but no leaks were found. Replacing the Intake Manifold Absolute Pressure (IMAP) sensor also failed to resolve the issue. The fault code would reappear intermittently, typically after a two-hour drive. Interestingly, clearing the code sometimes triggered a temporary check engine light.
The key to diagnosing the problem was recognizing a pattern: the derate condition consistently occurred 30 minutes after climbing to altitudes above 3000 feet. This observation led to the investigation of a potential barometric pressure sensor issue. Cummins engines do utilize a barometric pressure sensor, located near the IMAP sensor. After replacing this sensor, the fault code and derate condition were eliminated.
The experience highlights the importance of considering all potential factors when diagnosing engine performance issues related to intake manifold pressure. While leaks and faulty IMAP sensors are common causes, a malfunctioning barometric pressure sensor can also trigger the “engine intake manifold 1 pressure” fault code, particularly in scenarios involving significant altitude changes. This sensor plays a crucial role in allowing the engine control module (ECM) to adjust fuel delivery based on air density, which varies with altitude. A faulty reading can lead to incorrect fuel adjustments and performance problems.
