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PDM - Key on Capabilities

EFI Wiring Fundamentals

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Discussion and questions related to the course Motorsport Wiring Fundamentals

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Hey all,

I was wondering if it is possible to power a car on from complete off with a PDM and a CAN keypad or does this require some sort of physically switch to put the car in an on state?

Hi Michael,

There should be some sort of a primary master switch for the vehicle that isolates the battery from the rest of the vehicle, once this is switched on then (with the MoTeC PDM at least) the rest of the power up sequence can be completed either automatically (outputs turn one when powered) or through functions controlled by the Keypad or other devices.

Some PDM's will be able to do something like that.

From my own experience I know the AiM PDM32 has 2 different "On" states. A sort of "soft on" and also a full ignition on.

You can wire the PDM like this:

1. PDM Soft-on input has constant 12v from the battery.

2. Program the PDM so that the can-keypad is powered up during soft-on state.

3. Use one of the power outputs from the PDM to trigger the PDM's own ignition input.

The way I did step 3 is I spliced the power output that goes to the ECU, so that it also triggers the IGN input on the PDM. This way I don't waste a power output.

Important Note: Obviously this introduces a small parasitic drain on the battery while the engine is off. You have many options on how to deal with that. One option is just to ignore it, parasitic drain is basically par for the course on modern cars these days.

I dealt with it using a battery isolator, so if the car is going to be parked for an extended period of time, I just disconnect the battery with the press of a button.

The PDM is fully customizable, so you can have as many things on or off during soft-on as you want. But the more things you have on, the more parasitic drain you'll have. So use your own judgement on what you think you need there.

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