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Powering DTC via E7 pin

542 Views 10 Replies 6 Participants Last post by  Lotus
Hey ya'll, I'm super confused on this, I have an 2005 Accord ECU I'm trying to power the DTC when the car is off to save emissions data. I tried to hook up 12v to pin E7
via the coil side of a relay and I think I fried it instead.

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Looking at the diagram I see that pin E7 is hooked to the Main Relay on the coil side and constant 12v is on the other end of the coil.

Well I don't know if thats the whole story as now my E7 won't go to ground it just drops from 12v when the car is off to 2.4v when the car is in position 2. If I order another ECU I don't want to fry that one too trying to power the DTC. Is there a better way to do this?

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Anyways this is what it says for the pin. Thats why I figured I'd have to figure out some way to jam 12v into it when the car is off.

This person had the same question but of course no one answered them :cry::

Any help would be appreciated!


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There is 12V from the battery on one side of the main relay coil. The other side is connected to the ECU.
If the ignition is off, this coil provides 12V to E7 for that memory. The current is very low, hence the coil resistance hardly drops any voltage. If you switch the ignition on, the ECU detects the 12V on e9 provided by the ignition lock. The ECU then uses a transistor to pull E7 down to ground. Now a larger current flows through the main relay coil and activates it providing power the ECU itself, the coils, injectors and oxygen sensors (depending on ECU type).
So unless you unplug the ECU or the battery or switch the ignition on, E7 always sees 12V and powers the DTC memory. If you switch ignition on, the memory is powered as well.

if you apply a low impedance 12V source to E7 and you switch the ignition on, you’re in trouble. Unless the ECU has some over current protection on this pin, you’ll fry the output transistor in the ECU.

I don’t get that DTC memory save thing?
It is only ever erased, if you unplug the ECU or the battery.
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12V(Batt)-----RelayCoil(main relay)------E7
that powers the memory with ignition off

12V(batt)----ign lock-------e9
that activates the ECU to turn itself on and trigger the main relay by pulling E7 to ground. This in turn provides 12V to the power parts of the ECU, injectors, coils etc.
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