06 CRD wont crank on key but cranks bypassing starter relay but doesnt run

[3bar]

Ok so heres what I can see / done and tearing hair out.......

This first started out as a rare / occasional / intermittent problem of occasional no start but now it drove into the garage and doesnt want to leave

1) Key on - everything normal - the red immo light goes on for about 2 seconds then goes off (same behaviour on both keys) red immo light doesnt flash or stay lit - if using the key - see point 8

2) trying to start - it doesnt crank, just a momentary click from probably the starter - but its not a dead battery - battery voltage 12.9, on a charger / paralleled to another battery on the floor - if i keep the key turned to the start position, the click is every second (tonk - tonk - tonk) the radio goes off when trying to start

3) if I short out the starter relay with needle nose pliers - the starter cranks the engine over perfectly- which is why this doesnt feel like a battery issue

4) starter has been pulled out and bench tested and it works perfectly

5) I have used an obd tool with a key addon, it verifies that both keys transponders are present and identifiable

6) the obd tool verifies that the coil around the ignition barrel is working and receiving the signal from the transponder in the key

7) there are no codes in the SKIM / SKREEM module (there were from unplugging / re-plugging with power on) the only code is a known issue with right front abs sensor

8) ignition switch has been seperated from the key barrel so a screwdriver can actuate it - same result (the key is inserted into the SKIM antenna circle and the red immo light goes off after 2 seconds and doesnt flash / stay on - unless I force it to, by removing the key from the SKIM antenna and trying to start using the ignition switch with a screwdriver

9) the ignition key barrel rod etc - is 100% nothing broken - the behaviour on the screwdriver actuating it versus the key is 100% the same

10) Relays have been swapped over with other ones with matching part codes in the relay box - no change

So if its not the immobiliser, key switch mechanism, relays - what else is causing this ?

What wires etc could have "voltage drop" on them - seems to me the "relay" isnt being triggered hard enough by the key ?

is that possible ?

What all to check ?

open to any and all ideas on this

Thanks for reading

 

[lfhoward]

Do you think the "click" sound is the relay or the starter? If the relay clicks but the starter doesn't move, try removing the actuator wire from the starter (that energizes when you turn the key) and cleaning it. Sometimes there is enough corrosion on this connection to keep the starter from getting the message that it is supposed to wake up. This situation happened to me with my 4.7 Jeep Commander, and like you I explored the ignition actuator and other things before testing this simple connection. It turned out the connection of this wire to the starter was the issue. In the Commander it was a yellow wire. Not sure about what color it is on the KJ/KK.