[golfpro]

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.

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?

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 :

K-Swap Wiring 1-Relay E7 MRLY - EK Civic

Hey guys, I'm making my own K-swap conversion harness and I'm 95% done but there is one thing I can't figure out. I'm only using 1 relay for the A/F sensor and re-using the stock EK PGM-FI Main relay. I need to know how E7 (MRLY) gets Voltage Backup (VBU) in a 1-relay setup as it requires...

www.k20a.org

Any help would be appreciated!

 

[golfpro]

Ok this is interesting

Technical Information K20 Swap Wiring

www.hondata.com

"Do not wire the main relay (E7) or fuel pump (E1) to 12V. This will damage the ECU. Both E1 and E7 are outputs which switch on relays by grounding the ECU output and do not like being forced to eat 12V "

But look at their diagram...

It shows constant 12v going into the main relay as well, but it says ECU in the little dialog. What does that mean? Does that just mean constant but fused for the ECU?

 

[Bjorn]

Ok this is interesting

Technical Information K20 Swap Wiring

www.hondata.com

"Do not wire the main relay (E7) or fuel pump (E1) to 12V. This will damage the ECU. Both E1 and E7 are outputs which switch on relays by grounding the ECU output and do not like being forced to eat 12V "

But look at their diagram...
View attachment 111179

It shows constant 12v going into the main relay as well, but it says ECU in the little dialog. What does that mean? Does that just mean constant but fused for the ECU?

I think this identifies the 'ecu fuse' just like the fuel pump example identifies the 'fuel pump fuse'

 

[Humphryorg]

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.

View attachment 111178
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?

View attachment 111177
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 :

K-Swap Wiring 1-Relay E7 MRLY - EK Civic

Hey guys, I'm making my own K-swap conversion harness and I'm 95% done but there is one thing I can't figure out. I'm only using 1 relay for the A/F sensor and re-using the stock EK PGM-FI Main relay. I need to know how E7 (MRLY) gets Voltage Backup (VBU) in a 1-relay setup as it requires...

www.k20a.org

Any help would be appreciated!

Sorry, this is too complicated for me to understand

 

[Brotatochip]

Sorry, this is too complicated for me to understand

Then don't reply

 

[Brotatochip]

E7 is the relay control as specified in your circuit diagram, it is not an ignition input. The relay it turns on then gives itself power on pins A2 and A3.

I'm confused what the purpose of this is? Why can't you just turn the key on to save data?

 

[Lotus]

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.

 

[wesara4513]

Well^^


Sent from my iPhone using Tapatalk

 

[Brotatochip]

Well^^


Sent from my iPhone using Tapatalk

Are you a bot?

 

[golfpro]

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.

My recent thought is what I'm messing up is I'm powering the ECU via the switched ignition circuit thus the ECU is powered before the ECU tells the relay circuit to power itself on, but it seems you're saying that when the relay coil is powered its acting as a load thus not cooking the E7 transistor? I guess that makes sense too.

I've got two "new" ECUs and I'll try to make that double relay circuit as close as possible. I'm not sure why powering off the car clears the memory but it does. Probably something to do with my hacky wiring.

 

[Lotus]

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.