Daughter board communication error before crank

[josaya]

Issue: on cold mornings <10 degrees C (50F) I normally let the car do its diagnostic check, then crank. Was faultless for a few months, then suddenly started going into limp mode within 5s of starting the car. It would go away when the engine is fully warmed up. Like https://www.hondata.com/forum/viewtopic.php?t=19149, I lose all datalogging capabilities with my v4.

Have read through/actioned the stickied articles. Negative wiring has been checked. Battery is under 3 months old and is over 12v on start. As a test, I've left it pre-crank and its fired up the error without starting. Frustrating as it only decided to start happening 2 days before putting the car through pits and obviously it failed. Have pulled out all electrics, daughter board etc look OK) no burns, capacitors look ok. As it goes away after a while, it is frustrating to diagnose!

Any clues would be appreciated.

[Spunkster]

Check the battery voltage at the ECU using a multimeter during start and see what it is doing. It is probably dropping too low and that is causing the issue.

[josaya]

Ok, thanks again! Will have a look later in the day

[josaya]

Check the battery voltage at the ECU using a multimeter during start and see what it is doing. It is probably dropping too low and that is causing the issue.

Have checked both +ve from the ecu, both are 12v/14.2v pre/post crank (before and after the starter motor has clicked).

LED's on the Kpro started doing the following:
Ignition on-> Green turns on for 1-2 seconds, Red starts flashing. Starter motor clicks.
Green turns off, Red still flashing
Engine Check light turns back on ~5s after, I lose data logging ability

Removed kpro from ECU and re-seated in a static environment. Now no error. Will be happy if it doesn't do it tomorrow, but I'll go with https://www.hondata.com/forum/viewtopic.php?t=9028 and update with answers\questions after I rip out the dash wiring

[Hondata]

What you need to do is check the battery voltage to the ECU while the starter is cranking the engine.

[josaya]

So started perfectly and stayed perfect this morning (under 5 degrees) drove to work.

Upon return to vehicle 9hrs later, it started happening again. Except the check light has stayed on even when warm.

What you need to do is check the battery voltage to the ECU while the starter is cranking the engine.

Cheer for clarification, however both igp2 and igp1 are roughly 12.5-12.8v on ignition, 10.1-11.5v during crank, and works their way to 14.2 post crank (tested multiple times hence range)

LED behaviour:
Ignition on: green turns on for 1-2s, red starts flashing
Green goes off, red keeps flashing.
Eventually check engine light turns itself back on and engine is limited to 4k.

Edit: plugged in the laptop, error went away on next crank... Tried a few times (~10x without laptop plugged in), and it is still gone, but that leaves me where i was at yesterday. I should "cycle the ecu" according to https://www.hondata.com/forum/viewtopic.php?t=4877. Can someone please describe this part?

Crank volt dropped to 8v on first crank turn in datalog, then up to 11 on subsequent turn, although multimeter doesn't pick it up. Maybe battery? Although only 3 month old 430cca battery. That or redo the grounds again, and replace the ground connector.

Thanks in advance, again.

[Spunkster]

It could be the battery , grounds or the wiring to the ECU. You will have to use a multimeter to try and find where there is resistance which is causing the voltage to drop.

[josaya]

It could be the battery , grounds or the wiring to the ECU. You will have to use a multimeter to try and find where there is resistance which is causing the voltage to drop.

Yeah I agree. Will be this weekend's mission. I suspect it is the battery or wiring to ECU, as grounds were recently done (but will redo and check them again)

The strange part (same with some of the other threads) is that the ECU already detects the voltage drop even before it has cranked when the voltage to the ECU is still above 12.5V (aka you first turn the key into the "ON" position to do the engine \electronicscheck etc). I say this as it is already doing the green light on\off + red light slow flashing thing beforehand. Anyhow, thanks for the advise, will update next week.

[lammertime]

I have a similar problem.

https://www.hondata.com/forum/viewtopic ... 6&start=15

Interested to see what you find. My voltage to the ECU is consistently about .1v to -.15v below the battery. I don't play with it too much as I still have my stock ECU that works just fine.

[Jocker_666]

I have a similar problem.

Check my topic lammertime maybe it will help You somehow :).

https://www.hondata.com/forum/viewtopic ... 12&t=20478

[josaya]

I have a similar problem.

https://www.hondata.com/forum/viewtopic ... 6&start=15

Interested to see what you find. My voltage to the ECU is consistently about .1v to -.15v below the battery. I don't play with it too much as I still have my stock ECU that works just fine.

Yeah read Jocker_666's post... i posted the most commonly found "items" that have resolved it, excluding his solution. I'm working my way through that, an ecu solder may be my last port of call. Not sure which one on the board is the 12v to daughterboard though, but I've seen some posts where people resoldered that and the issue went away :( Clean and reseat of the ECU might have fix'd Jocker_666's issue, but in my case, it didn't.

I've also noticed that when I use the laptop plugged in for a few minutes to get Kpro to work, voltage at to the battery\ecu is always very close to 13V which seems very odd. Have ordered 7.5A fuses as they're rare where I'm at, and going to replace every single fuse while I'm at it. I've also seen a solution where the fuel pump relay is the cause of the issue, so I might track one down as well. Very costly exercise, but once my re-wiring is done (a month or so at my rate...), I'll be running through the list.

[josaya]

Check the battery voltage at the ECU using a multimeter during start and see what it is doing. It is probably dropping too low and that is causing the issue.

What you need to do is check the battery voltage to the ECU while the starter is cranking the engine.

Hi Guys,
2x New batteries, old battery
Voltage to ecu is ALWAYS above 12V (tested from the ECU pin). Always 0.1-0.2v lower than at battery.
Turn key to start electronics test, kpro LED goes green for 1 second, then immediately starts (slowly) flashing red. Starter motor turns as normal.
Electronics check completes. Give it another 3-4 seconds. Check engine light appears.
Turn key to ignition, motor fires up with no dramas. Check engine light still on, kpro still slowly flashing red.
I've checked this against a bseries engine, and that has a larger voltage drop with no issues.

Just to be clear... car\ecu was running fine for a few months, nothing was changed, then this started happening. I've checked all positive and negative terminals on the engine to\including fuse box.

Are you able to tell me which pin on the ECU\kpro provides the kpro with voltage?