My 1609 Sigma very often does not see the cadence sensor. It will work again 1 or 2 days later without doing anything to it. I have tried batteries & made sure the sensor is close enought o the magnet. Any ideas?

Wired or wireless?

I have a 1609 wired. I've been having the same problem with both cadence and speed. I can usually get the speed to come back by wiggling the computer back and forth on the mount (same motion as if I was removing the computer from the mount and replacing it, but without twisting it far enough to remove it).

The cadence seems to cut out less often, but when it does, I can't get it to come back the way I can with speed - it usually starts working again in a ride or two.

I bought mine six months ago, and have been planning to ask for a warranty exchange - but perhaps this is a design flaw, rather than a defect with my unit?

Funny, The 1609 uses the same pickup and magnet as my 1606 and I haven't had any problems with the pickup. How is the space between the pickup and magnet? How is the connection at the head?

I don't know about the OP, but my problem does not seem to be a magnet/sensor issue. The magnet is very close to the sensor (about a mm perhaps?). Wire connections to the mount seem fine. Also, the problem often occurs when pressing buttons, and can be rectified by wiggling the computer around on the mount, while messing with the magnet/sensor, or the wiring near the mount does nothing. As far as I can tell, it seems to be an issue with the connection between the mount and the computer, though I suppose it could also be a problem within the mount or the computer.

I wonder if the connections in the unit are bad or if they changed them so much on the back of the unit maybe they don't make good contact with the connectors on the mount. For example if they made the contact points on the unit shallower than they used to be then they wouldn't contact the flat pick up on the mount. I did just get a new universal mount for a second bike setup and it doesn't seen near as stiff as the original mount even though it looks the same

At an auto store you can get a dielectric grease (usually for spark plugs and wires) but it is useful on any electrical connector to prevent corrosion and allow full electrical connection. You might try a dab of that on the unit contact points for the mount. Otherwise contact Sigma and get them to replace it or get an older 1606.

If you have a wired unit, at least my 1606's cadence sensors plug into the computer base with a pair of connectors. Like any contact exposed to the elements, the contact area can become contaminated or corroded. You could just pull the wires off the pins and re-install them. This wiping action might clear away any gunk or corrosion, but it also might not. There should also be some significant pressure between the pin and the round contact on the wire. If there isn't, you can GENTLY squeeze down the contact on the wire, using a needle-nose pliers. This is risky, however! It might not be difficult to crush that contact.

But, I haven't really had any problems with my two 1606's. Have they cheapened the contact design on the 1609?

Mine is the wireless unit & all is adjusted correctly

Are you running any lights or other electronics?

No other electronics at all. Sigma advised using the reset button to synch the unit with the sensor