Tach suddenly reads low

[clarknova]

2006 smart fortwo pure CDI

 

Last week the tachometer suddenly started reading low. With the engine off, it show 0. Idling, my iCarsoft says 850, the analog tach says just over 500. Cruising at 100 km/h (GPS, 104 on the speedo), tach says ~1600, icarsoft says 2250. In neutral if I idle it up until the tach says 2000, the icarsoft says 2700.

 

In all cases I believe the icarsoft, as I have another smart that would show similar numbers under that same circumstances, as would this one until recently.

 

Not sure how relevant it is, but just before this happened, the car refused to crank. A mechanic found the power wire was backed off the connector on the starter and he pushed it back on. I don't know what else might have happened while he was in there, but that's what he reported.

 

What should I be looking for to fix this?

[stickman007]

I’ve seen this before on a smart that I had worked on. Ended up being the SAM - the guy had corrosion due to a water leak at the windshield.

 

Good Luck

[clarknova]

Thanks, I'll go looking for that.

 

I forgot to mention, it has also stopped displaying the remaining fuel when it gets to 5.0 L. Again, the icarsoft can tell me an accurate % of fuel remaining, but the instrument cluster simply starts blinking the fuel icon when it gets below 1 dot.

[clarknova]

@stickman007, is the SAM replaceable? Would the dealer then have to code it to the car?

[MikeT]

Yes and yes. About $1200 last time I had one done.

[stickman007]

If you buy a used SAM, then you’ll have to use special tools to “clone” it. Otherwise you’ll have odometer mismatch and possibly programming issues.

 

if you buy new from the dealership, then it’s just expensive.