12v only when motor running - need source (1 Viewer)

[Jeff Elliott]

Hi All -

Installing a wideband AFR sensor which needs 12v only when the motor is running. Wondering what source for this you might suggest?

Many thanks!

 

[gnob]

Afaik there aren't too many sources that are "run only".
Off the top of my head, the fuel pump feed is about the only one i can think of.
Is there some reason you can just use it in key on?
Otherwise just wire it up and use a switch.

 

[Jeff Elliott]

Thanks @gnob - yes, the reason for "run only" is that this source would provide power for the wideband probe. From what I've read, these probes heat themselves up to deal with the exhaust temps and to prevent condensation from "fouling" the sensor. If they power / heat up too early (say with accessory power), it shortens the life of the probe.

 

[jht3]

would the same not be true for the OE o2 sensors?

i *think* anything after the "circuit opening relay" is going to be run only. this includes the fuel pump relay and fuel pump. the EWD doesn't say - or i can't find - when the ECU grounds pin 14, labeled FC. that relay should be in the drivers side kick panel.

 

[Malleus]

Jeff, the first thing that comes to mind is the charging circuit, which is only active when the alternator is spinning, but I'd hesitate to tap into that. You might be able to construct a circuit that performs similarly, though. Here's the power source circuit detail info.

The second thing that comes to mind is the seat heater circuit, which is probably ununsed on your model. The taps should be on the floor near the front of the center console.

 

[Jeff Elliott]

Thanks @Malleus - I will probably grab that charging circuit as a trigger for a relay that provides 12v for the probe. Will report back with outcomes.

 

[clx16]

O2 sensor heater circuit via relay, but that might even cause a code

 

[Rwhat]

Cigarette lighter. Only works with key on. That’s what I use for a 12v source to trigger a relay for my dual battery system. Don’t over think it.

If your worried about the probe being on too much, then wire up a low amp colehersee continuous duty rely that will trigger the relay closed at 13+ volts. So basically when the alternator is charging it will turn the AFR on.

 

[fjbj40]

Jeff, the first thing that comes to mind is the charging circuit, which is only active when the alternator is spinning, but I'd hesitate to tap into that. You might be able to construct a circuit that performs similarly, though. Here's the power source circuit detail info.

The second thing that comes to mind is the seat heater circuit, which is probably ununsed on your model. The taps should be on the floor near the front of the center console.

This is the source I used for my aux fuse box relay. I used a fuse tap in the under hood fuse box for that circuit.

Works perfectly fine so far….

 

[robnicko]

does your truck have the 12v power outlet near the washer bottle? Use the Ign feed

 

[Malleus]

Cigarette lighter. Only works with key on. That’s what I use for a 12v source to trigger a relay for my dual battery system. Don’t over think it.

If your worried about the probe being on too much, then wire up a low amp colehersee continuous duty rely that will trigger the relay closed at 13+ volts. So basically when the alternator is charging it will turn the AFR on.

Missed that one; and it has its own fuse. Bonus!

Might not work for you if you have to have the engine running, though. The circuit is active when the key is ACC or ON (see page 2), so it doesn't depend on the alternator but the battery. Still, good to know.

 

[jpoole]

When I've run these wideband o2 driven afr gauges I've wired them to key on. One benefit to this is that you can free air calibrate the o2 sensor without needing to run the engine. Depending on mount location you may need to pull the o2 sensor from the bung or you may be able to let things sit overnight and then effectively recalibrate in the AM. You can also run through a reset/reboot without cranking the engine for each power cycle you may need to perform. Not sure which system you are installing but you may want to read through the manual on those procedures (if they apply) to make sure you are powering this in a way that will make it easy to manage.

You'll enjoy the AFR gauge. It's a huge asset when setting and monitoring engine tune in my experience.

 

[Jeff Elliott]

Thanks to all! Great feedback and ideas! I'm going to have a go with the charging circuit and will report back on results.