Pre-Power Wiring Recommendations

Unlike your vehicle's ECU the MAFT Pro and (if you have one) your wideband oxygen sensor require a few seconds to boot and begine outputting data. The ECU in most vehicles boots more quickly and expects the signals now provided by these add-ons immediately. The brief delay most often results in the vehicle's ECU storing diagnostic error codes. In many cases these do not cause the ECU to modify the operation of the vehicle once the signals have proven reliable, but preventing these codes is always the surest bet to avoiding undesirable or unforseen effects.

Method One
Dual circuit power

If you're powering your MAFT Pro and wideband via their own circuit through a relay (strongly recommended) this is possibly the simplest method to ensure the MAFT Pro has time to boot is to power it up prior to the ECU powering up. This is accomplished through the use of a relay and a couple diodes to provide power to the MAFT Pro once the key is turned to the accessory position and thereafter.

You may be wondering why you don't just run the MAFT Pro off of the accessory circuit. The answer is that when the engine is cranked most vehicle power systems remove power from all circuits not essential to the running of the engine and the starter. So, we need to power the MAFT Pro from a circuit which remains active at that time as well... So, we'll use the ECU's switched power line.

In order to prevent the ECU from powering up before it should and to prevent everything on the accessory circuit from drawing power when the engine is cranked we need to isolate the two signals from eachother. Hence the diodes. I won't go into the specifics, what you need to do is shown below... just know that the diodes are ESSENTIAL.



Once you've wired everything up as specified you'll need to make sure that you follow the notes in the diagram below when you start the car. Failure to pause at the "ACC" position when starting the car will result in diagnostic error codes being stored. These will need to be cleared.

MAKE SURE TO PLACE A FUSE BETWEEN THE BATTERY AND RELAY!!!

Method Two
Delay Throw or Delay on Make Relays



An alternate method is to delay the power supply to the ECU. This would be accomplished by rerouting the power to both +B and +B1 through a delay throw relay... aka 'delay on make'. The nice thing about this method is that you needn't pause at ACC when turning on the ignition. The only downside is that in an emergency you're waiting the preset number of seconds... unless you thought ahead and installed a bypass (which you should do in either of these setups anyway). With the aforementioned method you may start your vehicle immediately any time you wish, you'll simply need to clear the error codes later. The delay relay is friendlier when combined with remote start systems though.

Given that I intend on powering my wideband and MAFT Pro via their own circuit it was a given that I would need to use a relay.. so one extra wire and a little forethought (until it became habit anyway) saved me some more wiring and a few bucks. If you do choose to go with a delay relay, I still highly recommend powering the MAFT Pro and wideband seperately from the ECU. I do admit that I like this method, if for nothing other than its failsafe nature.

Here's one source for a delay relay (thanks to James, aka JustJeeves): WEISD.com