2006 Diesel Accord starting problems - any help appreciated!

[Alexz150]

Hello



I bought a 2006 Honda Accord in January which came with what I suspect is an ECM/PCM fault – the key has to be turned between stops 1 and 2 many times before the green key light will stop flashing and the VSA light disappears. At this point the engine and coil light come on, go off and everything works fine.



If you don’t do this with the key, the car will crank fine but is immobilised, hence the flashing green key, I am guessing because the ECU does not reset/communicate correctly with the other components. There is a parasitic current draw because if you charge the battery, it will go down to about 11.4v if left, and goes flat quickly if the key is left in.



Another odd quirk is it seems to prefer very cold weather for the ECU to turn on  My only guess is a temperature sensor connected to the ECU is PTC type and provides some sort of ground to the ECU when it’s cold outside causing it to reset. Could be talking out of my *** there though.



I’ve read up elsewhere about this fault but only seen one other post anywhere with the same issue, here it is:
https://www.civinfo.com/threads/dies...oblems.101774/



I’ve tried:
- Ensured battery is topped up
- Replacing key battery
- Tried the spare key
- Replacing the receiver ring (changed back because it did not fix the issue)
- Checked fuses
- Pushed the center console and under passenger wiring harnesses around by the ECU whilst shifting between ignition stops 1 and 2
- Read through the factory service manuals and electrical schematics
- Bought and plugged in a MVCI GNA600 HDS clone, but it would not connect because the ECU doesn’t start up.
- Fiddled with the passenger relays out of frustration



Things I have not yet tried:
- Oscilloscope on the CAN lines
- Trying HDS clone with ECU working


An OBDII test shows ABS pump relay open circuit and body ground issues but when you can start it the ABS works if you stamp on the pedal and grounds in the center console are 30ohms to negative battery terminal. That 30ohms is all made up on the wire from the terminal to the body in the engine bay.


Should I take the ECU out and visually inspect the board? The car is on 207k so guessing is about time for it to be serviced.



I have been sitting in the car shifting between ignition stops 1 and 2 all day whilst on charge because the battery was flat, witnessing all sorts of strange behaviour from the computer when drawing lots of current by moving the power seats or windows, namely the display saying “ABS check system” or the stereo display flickering – but no signs of life from the ECU  When I got the car, it would only take one or two shifts between 1 and 2 but seems pretty dead now.



I am pulling my hair out – any help is appreciated!
Alex

[Trevor]

Hi Alex....welcome to the Club

My absolute first thoughts are battery supply and earth returns.
If you are experiencing issue with immobiliser and also ABS then I think I would trace through from the battery (both sides) and work through the fuseboxes and other current supply routes to see if there is any corrosion or breaks in wires, etc.

I know its like teaching you to suck eggs but I have fallen foul of some of the simplest faults which I failed to initially check