A 2006 Ford Expedition presented with a rough idle, non-functional temperature gauge, limp mode, and a P1289 Cylinder Head Temperature (CHT) sensor code. The vehicle struggled to maintain idle and lacked power, barely reaching 50 mph. This article details the diagnostic process and solution.
Identifying the Root Causes: Vacuum Leak and Faulty Wiring
Initial diagnostics revealed a vacuum leak originating from a cracked fitting on the intake manifold’s rear passenger side, connected to the brake booster. Repairing this leak resolved the rough idle issue. However, the hesitation during acceleration, lack of power, and non-functional temperature gauge persisted.
Further investigation focused on the CHT sensor wiring. The engine pigtail connected to the CHT sensor showed signs of a previous repair, with a soldered and heat-shrunk splice exhibiting significant corrosion. This connection is located behind the engine, above the transmission bell housing, and uses a two-pin round connector.
Repairing the CHT Sensor Wiring
To access the sensor, the alternator was removed, and the connector was carefully detached using a long screwdriver and pry bar. The corroded pigtail was replaced with a new 28-inch wire, routed around the front of the intake manifold.
Post-repair, an OBDII scanner confirmed successful temperature readings, indicating a restored connection. Crucially, the live data stream initially displayed a constant 55 degrees Fahrenheit, highlighting the faulty sensor’s inability to report accurate engine temperature.
Diagnosing P1289 on a 2006 Ford Expedition
If your 2006 Ford Expedition experiences similar symptoms, including a P1289 code, begin by checking the engine temperature using an OBDII scanner. A stuck temperature reading, particularly around 55 degrees Fahrenheit, strongly suggests a faulty CHT sensor or wiring issue. Inspecting the CHT sensor wiring for damage or corrosion is crucial. Addressing any wiring issues, as outlined above, may resolve the problem. Don’t overlook seemingly minor issues like vacuum leaks, as they can contribute to performance problems. This case demonstrates the importance of thorough diagnostics and the interconnectedness of various engine components.
