Aston Martin DB7 I6, 1997 - Immobiliser issue

[paralis]

Hi Folks,

have an issue with the immobiliser, car cranks but will not start, fuel seems to be cutted off from the immobiliser ecu, but immobiliser seems to work somehow, because the red light vanishes when I turn the key to ignition.

It started today, when I was unable to open the door with the remote, I used the original key to open the door, the alarm turned on. I inserted the key into the steering wheel lock but hazard still continued to blink, then I tried to started the car, but no luck.

did the following tasks to solve the issue with no success :

1. disconnected battery for 2 hours
2. bridged + and - (without battery) for 2 hours
3. locked/unlocked the door with key
4. locked/unlocked the door with remote fob
5. checked all fuses
6. checked the security ECU under the battery (it´s not a cobra), modul is from f+g megamos GmbH, SPD 5895 315MHz, disconnected and connected
the modul.

Any help is appreciated

Thanks
Frank

Edited by paralis on Tuesday 21st September 20:14

[N7GTX]

When you put the key in the ignition the red immobiliser light goes out but the car will not start? Have I got that right? The fuel pumps do not run but the engine turns over?

If so put the key in the ignition as usual and watch the red light go out as normal. Now when you turn the key to the position before starting, that is all the lights come on the dash, check they all light up. Does the light with the engine symbol come on?

If it does and the fuel pumps do not run then suspect the fuel pump relays in the boot. You can bridge them as an emergency measure to see if the pumps will run or if you have a multi-meter you can check if you are getting power to them. The pumps can fail at any time so test them too.

If the engine light does not come on then locate the main relay in the fuse box under the steering column (I think its in that one). Without the main relay the engine ECU is not powered so no light on the dash and therefore no power to the fuel pumps etc.

[paralis]

Hi N7GTX

thank you for your reply,


When you put the key in the ignition the red immobiliser light goes out but the car will not start?

• YES

The fuel pumps do not run but the engine turns over?

• I can hear the pump for about 5 seconds when I turn the ignition on. The engine turns but will not jump

If so put the key in the ignition as usual and watch the red light go out as normal. Now when you turn the key to the position before starting, that is all the lights come on the dash, check they all light up.

• YES all up

Does the light with the engine symbol come on?

• YES

If it does and the fuel pumps do not run then suspect the fuel pump relays in the boot. You can bridge them as an emergency measure to see if the pumps will run or if you have a multi-meter you can check if you are getting power to them.

• OK

The pumps can fail at any time so test them too.

• OK

In one of my endless efforts to get the engine running, I used Engine Starter Aerosol Spray but even with that, the engine didn´t cough at all, nothing. I can´t smell petrol on the exhaust tips and the spark plugs might not getting power, this all points to the immo system in my opinion, but I hope I´m wrong.

Is it possible when I cranked the car with the red key and the alarm was still running that the engine ECU blocked the Key permanently ? The PAT system
seems to work fine, because the red light turns off after 3 seconds when I turn the key into ignition mode on position 2. I assume the PAT system sends
a OK message to the ECU but the ECU don´t care because it has blocked the key.

[N7GTX]

I think you need to go back to basics. The red light is working from your description. When you turn the key to ignition on the fuel pump will run for up to 5 secs to prime the fuel lines with pressure. So now when you turn the engine over to start try these basic tests.
Remove the plug lead from the front cylinder and using an old spark plug, put the plug into the lead and then rest it on a metal part of the engine - the alternator bracket is close by. While turning the engine over ensure you have a good spark.

If you do have a good spark you now need to ensure you have fuel pressure in the fuel rail to the injectors. Ideally with a fuel pressure tester. You could turn the engine to start for a couple of seconds then slacken the fuel rail at the pressure regulator but there is a fire risk if petrol is sprayed over the engine. The pressure needs to be around 35psi which will spray out when you slacken the connection.

If there is no spark then you need to test the plug to the ignition coil to see if it is getting a signal. If it is then the coil may be suspect. If it is not then you will need to use diagnostic equipment that can show the engine speed when cranking and to check for fault codes. If there is no engine speed showing then the crankshaft sensor is suspect.

A good source of help for the DB7 is the Aston Martin DB7 Appreciation Society on Facebook. Once you join you will see under Files on the main page free downloads of the manual and the parts manual. Also, one of the contributors is an expert on the immobilisers on these cars.

[paralis]

I will do all the testing as you mentioned, thanks for the surprise about the Facbook DB7 Appreciation Society that I joined today. A really good source.

[paralis]

Hi,

you were absolut right regarding "back to the basic"

The problem has been solved.


When I started the car with the alarm running, the ignition coil died instantly, so I thought IMM Problem.
I ordered a new ignition coil a couple of days ago, because I had some dropouts with the engine
and I thought this might be the ignition coil.


I installed the new one and now everything is working fine as it should and the dropouts are gone as well


Thank you again for your support and pation


Frank

[N7GTX]

Well done