prestige aps687a tach problem

ok i have this unit fitted on my daily driver, and has been working for months and worked perfectly this morning and now this evening it no longer detects the tach signal i've checked the wiring and there is a signal (~6v) at the remote starter end of the tach wire. The car starts and runs perfectly using voltage sensing but i'd like to figure this problem out has anyone seen this before? car is a 2003 Taurus if that helps

have you tried to relearn the tach signal?

Look at the serial number on the sticker on the back of the unit. There'll be four digits, a space, and then a whole lot more digits..........what's the digit after that space? That is, what's the fifth digit of the serial number? If it's a 0 or a 1, those units had a defect on their tach input. It seems to be even worse on Toyotas, many, many of them come back with this problem. You can either exchange it for a unit with a serial number of 2 or greater, or live with voltage sense, or build a special circuit with a capacitor and resistor to fix it. Go to techservices.audiovox.com and you can read the beginning of their bulletin about this. If you sign up for a free password, you can read the rest of it, including how to build the repair circuit.