Joe_H
Well-Known Member
With the other symptoms you describe - loss of trip data etc AND a normal start by connecting the battery to the solenoid activation coil (even if battery V is low as you indicated), then it is almost certainly not the solenoid. The solenoid would also NOT cause issues with the trip meter etc.Theory is sound ! Still keen to know what is actually in the immobiliser circuit (that would allow that level of volt drop) with the current drawn. I'm thinking, by the loss of fuel gauge and trip data (as these are fed from the same pcb) that the circuit is shutting down at a higher voltage than that required to turn the engine. Have a solenoid repair kit to fit anyways. Just trying to resolve this as the winter will surely bring it to a head ! Fully charged battery gives no probs....but it ain't right. If the battery can turn the engine, then the designed circuits should do it too.
A dodgy high current feed or earth with resistance WOULD cause these issues and is exacerbated by lower than normal battery voltage as described above.
You have already proven that the issue is between the starter relay and the solenoid as bypassing the relay and connecting the battery POS terminal directly to solenoid activation terminal works! - even with the lower charged battery.
As other circuits are affected then the main feed to or from the high current side of the starter relay , including the live feed to the fuse box in the engine compartment, and the grounding - is the primary suspect.
If the solenoid was at fault it would be highly unlikely to work with a more depleted battery by jury rigging the battery positive to solenoid.
It is DEFINITELY NOTHING AT ALL TO DO WITH THE IMMO CIRCUIT.
Measure between battery positive (note ! - not negative!) and starter solenoid terminal - this will give a reading of the differential voltage (drop) - which is exactly what we want - on cranking and is unaffected by actual battery load drop - as said above - because it is a differential measurement.
Then check the same between battery positive and starter relay supply and again check the differential. Repeat between starter relay input and output to solenoid (note - NOT from battery - between the two points this time).
The battery feed goes to the fuse unit cluster with the starter relay, then to the ignition switch and then to the interior fuse box and onwards to the instrument side.
There is no way that the voltage from the battery (unless it is totally captain cooked) - can drop to the level of resetting the clock unit - if the battery voltage is not being pulled down at the battery then it is not at fault.
This is all fairly straight forward fault finding Andy. Do not jump to unfounded conclusions regarding CCU unit etc. just work methodically through.
You have not supplied any figures at all from voltage measurements at differing points in the system during starting / when the fault arises.
To stress again - resetting of trip etc is definitely NOT related to a solenoid issue - it IS though HIGHLY likely to be related to a high resistance in the feed circuit.
A voltage drop due to resistance will show when measured ACROSS the circuit points - as opposed to always from the battery to the article(s) in question. It is usually FAR better and much more informative to measure from one positive part of a circuit to another when looking for a V drop / high resistance. Measuring from negative to point of interest tells us little if anything useful.
Always work on one fault at a time when there seems to be multiple related ones - as 99 times out of 100 you will solve the other issue by correcting the first.
I would immediately suspect a poor connection in the high current main supply from battery to fuse box p108 and that would be my first check.
With high current electrical faults it is almost always a problem further down the line rather than at the affected unit itself. Luckily the fault finding is straight forward if approached in a logical rather than scatter-gun approach.
Joe
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