I've been driving down a canyon at a very low speed so it has been possible to coast for the majority of the way. After a while of doing this, my check engine light came on. This is not the first time the light has come on after a prolonged period of coasting. Is there a correlation between coasting for a long period and the check engine light? Last time this happened, it went off on its own before I could take it in to the mechanic.

Were you coasting with the clutch in?

Not sure if this is the same symptom but I get a Check Engine High Temp light that comes on for about 2-3 seconds and then switches off. The dealer mechanic says someone in Michigan has the same issue and a fix will probably be out in November. Will just need to have the Fiat re-flashed to update the software.

Good Luck

The engine management system has simply detected an uneasonable set of readings.
The engine ecu monitors several sensors all over the vehicle, it knows if the car is in gear, if it is moving, if the engine is running, if the clutch is up or down.

If the engine ecu sees that you are moving for a prolonged period of time with the engine running, but not in gear, it naturally assumes that the speed detected will decrease as you are obviously drawing to a stop. But if the speed signal is maintained for a long enough period, the failsafe programming decides this is unreasonable and will record a fault and illuminate the EM light on the dash. The error could be logical (speed sensor feasibilty error), or more obscure (gear position sensor) the vehicle is moving yet the gear is in neutral, or (clutch sensor). Either way poor driving technique will be picked up as a possible error. Fiat sometimes update software which may address issues such as this but I dont think this would be cured by an update as its driver caused. If you were thinking that you were saving fuel by driving like this, you would be wrong, on over run the fuel injectors are switched off and so no fuel is introduced to the engine, so by driving down on idle you actually use more fuel.

If you coast in gear, I always feel like I slow down much faster than in neutral because of engine braking. While you may be injecting less fuel, the amount of fuel you then spend on speeding back up should you need to may be more than the amount of fuel you spend idling the car in neutral when going down a hill for a prolonged period of time. Naturally it depends on the inclination of the hill, if you still speed up or maintain speed in gear, then naturally staying in gear is a better choice because you use less fuel and wear out your brakes less due to engine braking. This is what the Fiat econ-something software might come in handy for. I'll be checking it out tomorrow.

mishaparem said:

If you coast in gear, I always feel like I slow down much faster than in neutral because of engine braking. While you may be injecting less fuel, the amount of fuel you then spend on speeding back up should you need to may be more than the amount of fuel you spend idling the car in neutral when going down a hill for a prolonged period of time. Naturally it depends on the inclination of the hill, if you still speed up or maintain speed in gear, then naturally staying in gear is a better choice because you use less fuel and wear out your brakes less due to engine braking. This is what the Fiat econ-something software might come in handy for. I'll be checking it out tomorrow.

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It is always best to stay in gear. You have far less control over a car in neutral.