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Sometime in the last decade or two, ignition system computers got an "upgrade" that monitors the voltage output of the battery before trying to start the car. However, the battery may have enough juice left in it to move the windows, seats, play and run electronic stuff, like a gps monitor, radio, windows, mirrors and seats. I suspect insufficient voltage in some cases can damage some delicate electronics and so they felt it necessary to prevent a low-voltage battery from accessing them.
Just sort of guessing on the "why" of it.... *headscratch*.
Thanks for reply, I've got a couple of things to try then I am going to have to give the car to a specialist as when it comes to the ECM and TCM i'm out of my depth. I was trying to avoid giving it to Aston martin as I have previously had my car returned to me in a dangerous condition and charged me a fortune for it. Can anyone recommend an electrical specialist near Burnham on Crouch, Essex (not Aston Martin)
What year is the DB9 you are dealing with? Is it the key and button type start or the so called emotional control unit?
What comes to mind if everything seems to work as normal and it just will not crank is:
The car does not know it is in Park: possibly an electrical issue with the buttons of the mechanical park release, there should be an indication on the dash what gear the car thinks it is in
Something with the brake pedal switch: in my later model the ECU surround lights red when pressing the brake before starting, if it did not light when pressing the brake I would suspect the brake switch
My car is 2008 and has the crystal emotion control unit. I will check the brake pedal switch. The brake lights work so I would have thought it was ok but I would imagine there is more to than that as you say the start slot normally lights up red when the car is ready to start and it is no longer doing that. Is there more than one switch on the brake pedal ? It may be something to do with the wiring from the switch to the dash ? I have had the dash apart but can find no obvious damage to the wiring or connectors to the switches.
Thanks for your input and as I said I will have a look at the switch.
If you push the key in to position 2 then the surround will be white with the brake off and turn red when you press the brake. You have to be careful not to go past position 2 and touch the start position when you put the key in.
Looking at the wiring schematics, it appears the brake switch is a double acting one (at least on a Virage like I have the diagrams for). One for the lamps, normally open and one for something else normally closed.
It is unclear where BOO SV and BPS go to, this taken from page 8.1 so this looks like a circular reference.
The key dock has a note about needing the brake depressed to crank but does not indicate where it comes from.
I have honestly never seen such a poor quality service manual as the AM one. Missing procedures, incorrect information. Wherever they spent the money from these cars, it was not on documentation.
If you push the key in to position 2 then the surround will be white with the brake off and turn red when you press the brake. You have to be careful not to go past position 2 and touch the start position when you put the key in.
Looking at the wiring schematics, it appears the brake switch is a double acting one (at least on a Virage like I have the diagrams for). One for the lamps, normally open and one for something else normally closed.
It is unclear where BOO SV and BPS go to, this taken from page 8.1 so this looks like a circular reference.
The key dock has a note about needing the brake depressed to crank but does not indicate where it comes from.
I have honestly never seen such a poor quality service manual as the AM one. Missing procedures, incorrect information. Wherever they spent the money from these cars, it was not on documentation.
I've got someone coming to have a look at it next weekend, ill pass this onto them. Thanks very much for info.
My manual V12 Vantage had something similar which turned out to be a starter motor fuse in the engine bay on that car. All the crystal key lights did what they should but dead silence when start requested.
As it turned out the posative connection on the stater was also not great due to a broken spring washer and was slightly looser than ideal.
However I think the fuse was degraded/stressed by me using the jump start location in the engine bay to raise my quick jack ramps. (did this only 2 days before the issue and bought myself a dedicated battery now for this purpose)
My manual V12 Vantage had something similar which turned out to be a starter motor fuse in the engine bay on that car. All the crystal key lights did what they should but dead silence when start requested.
As it turned out the posative connection on the stater was also not great due to a broken spring washer and was slightly looser than ideal.
However I think the fuse was degraded/stressed by me using the jump start location in the engine bay to raise my quick jack ramps. (did this only 2 days before the issue and bought myself a dedicated battery now for this purpose)
I think you may get more information on quality Independent Garages in your area if you look on the Aston Martin section of PistonHeads. There was recently a thread with UK recommendations.
I could only dream of having Bamford Rose 153 miles from me. They would be my absolute first choice even if an Aston dealer was directly across the street from me. Unfortunately my closest Aston dealer is 255 miles away.
I think you may get more information on quality Independent Garages in your area if you look on the Aston Martin section of PistonHeads. There was recently a thread with UK recommendations.
I could only dream of having Bamford Rose 153 miles from me. They would be my absolute first choice even if an Aston dealer was directly across the street from me. Unfortunately my closest Aston dealer is 255 miles away.
Thanks for reply, I'll have a look on Piston Heads
Unfortunately It still wont start, I have someone coming to have another look at it on Thursday so I have everything crossed. So far he has told me that the Engine ECU is not communicating with the Transmission TCU which could be a wiring fault, fuse issue or maybe the transmission control module is faulty or even a component failure like the start and gear select buttons in the dash.
