P128A Code MERCURY Cylinder Head Temperature
- Not within operating range
- Engine overheated
- Low coolant level
- Faulty Cylinder Head Temperature (CHT) sensor
- Cylinder Head Temperature (CHT) sensor harness is open or shorted
- Cylinder Head Temperature (CHT) sensor circuit poor electrical connection
How is the MERCURY P128A Code Repair Done?
Start by checking the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector pins.
What are the Possible Symptoms of MERCURY P128A Code?
- Engine Light On (or Service Engine Soon Warning Light)
What Does MERCURY P128A Code Mean?
The Cylinder Head Temperature (CHT) sensor is mounted in the cylinder head wall and is not connected to any coolant passages. The CHT sends a signal to the Powertrain Control Module (PCM) indicating the cylinder head temperature. If the temperature exceeds 126°C (258°F), the PCM shuts off four fuel injectors at a time. The PCM will alternate the four disabled injectors every 32 engine cycles. The four cylinders that are not injected with fuel act as air pumps to help cool the engine. If the temperature exceeds 154°C (310°F), the PCM shuts off all fuel injectors until the engine temperature drops below 154°C (310°F).