Your Fiat 508 engine control system detects a problem, the computer stores the diagnostic trouble
code C1644 in its memory.
To figure out what is wrong with your vehicle you must first extract the C1644 DTC For Fiat 508.
On 1999 and later C1644 Fiat 508 engines, the instrument cluster has a built-in self-diagnostic mode that can be accessed by pressing and holding the instrument cluster SELECT/RESET button. Insert the ignition key and turn to the RUN position (but don't crank or start engine). Continue to press and hold the SELECT/RESET button (for 5 seconds) until the word TEST is displayed by the odometer. Release the SELECT/RESET button within three seconds after the word TEST is displayed to begin the self-diagnostic mode.
C1644 Fiat 508 DTC Meaning
Chassis Code - Problem is controller area network wiring bus and modules.
MFG - Manufacturer Specific
Vehicle Speed Control And Idle Control System
Control Module Throttle Actuator Position Performance
Cruise Vehicle Speed/Set Speed Difference Too High
The original multi-displacement system turned off opposite pairs of cylinders, allowing the engine to have three different configurations and displacements. C1644 Fiat 508 code had an elaborate diagnostics procedure, including showing engine trouble codes on the air conditionning display. However, the system was troublesome, misunderstood by customers, and a rash of unpredictable failures led to the technology being quickly retired.