No diagnostics, no start!

[Ivan]

850 1995 T5,

Anyone know what causes the diagnostic reader to fail to read codes?
I can no longer even get 1-1-1. The LED has a very faint light which goes bright when the test button is pressed - but there is no response thereafter.

I can get the codes from the ABS and other control units (position 6 etc), but nothing from position 2 (ignition). However with the ECU placed in another car I can read the ignition codes (1-1-1) no problem.

The engine turns over but won't start. Battery is fine, ECU is fine (when placed in another similar car). With immobilier on, engine does not turn, with immobiliser off it turns but won't fire, and I can reprogramme the key-fobs no problems so I've ruled out immobiliser.

I'm guessing some sort of electrical problem on the car as the ignition part of the ECU doesn't seem to be powered up, where are the earth points? I've found a couple and cleaned them up, but didn't make any difference.

Things I've replaced or swapped...
The diagnostic unit itself (module A-B).
Fuses (all present and working).
"103" fuel relay, and the main relay next to it.
cam position sensor
crank sensor (rpm sensor).
rotor arm and dizzy cap
ignition coil pack.
HT leads
ECU connectors cleaned
There is plenty of fuel in the car.
However, I do not hear the buzz of fuel stage? I'm guessing lack of ECU power doesn't prime the fuel system (but it's not the 103 relay).

Could a failed fuel pump stop the ignition ECU from providing a diagnostic response?

!! puzzled !!

[Niles]

there's a fuel pump replay under the plastic cover on top of the radiator pack along with the radiator fan replay etc, they do have a habit of failing, well worth checking out. When you turn the keys can you hear the fuel pump priming? the pump is in the fuel tank, get a mate to turn the key & have a listen from inside the boot.

[Ivan]

Didn't know about that one - I'll take a look. Thanks.

[nobananas]

I had a similar problem a while ago. Had fuel pump (pressure at rail) had live at the coil but no spark at the plugs. I was fairly sure that It was a crank sensor fault but then found that I didn't have a 5 volt live at the crank sensor which was worrying me as that was supplied by the ecu !. Turned out to be a broken wire on that damn relay under that top radiator cover. The wires going into it are bent back on themselves, one was broken and three others the insulation had split, what a great bit of component positioning !

[Ivan]

That was the beastie! Same problem as bananas, the wires had been 'squashed' insulation broken and the copper wire had turned green and crumbled away. I guess this caused the relay to die. I've patched the wires and swapped in the relay from another car - fired up first time! Thanks Niles and Nobananas.

Just in case anyone has a similar issue the part number is 3545803, it prevented the car from starting even though the engine turned - and the diagnostics module was rendered inoperative.

[Tomcat]

Nice one NB, good to see a nasty problem getting sorted this easily, goes to show the usefullness of a forum like this.

[ben66]

This is exactly my problem, i've change the relay but still no joy. Where about were the wires corroded in your cases?

[Ivan]

they were corroded about 30cm from the relay itself.

[Jod T5]

Try the electrical portion of the ignition switch if the relay is clean....

Jod