GENERAL
Airbag article
Q On reading the article airbags, EVAP, misfires and wiper switch (CM Help!, January 2022, p78, VW EOS) I refer to the connection and re-connection of battery earth. The OP refers to ignition being on for both disconnect and reconnect of earth. You refer to Autodata and VAG as to ‘OFF’ when disconnecting the battery earth, ‘ON’ when reconnecting the battery earth. This may prevent power surges.
Can you expand a little please on this statement and indeed is it correct?
Brendan O Callaghan
A As mentioned in the article, it is the advice given by both VAG and Autodata that when reconnecting the battery, the ignition should be on, as this may prevent power surges. As this is advice from VAG (VW) and is correct then I suspect that they have good reasons for the advice. I can only surmise that the design of the electrical circuits is more conducive to allowing the current to flow on the connection of the battery with the ignition switch in the 'ON' position.
Like many procedures in the workshop manual, this process should be followed because it is given by the manufacturer and I am sure that in most cases simply re-connecting the battery with the ignition 'OFF' would cause no detrimental effect, but as this procedure has been outlined, it would be foolish not to abide by it.
GENERAL
Head sealants
Q A family member car – Audi A4 1.8T – has suffered a leaking head gasket after more than 20 years service. A test carried out at the garage detected the presence of exhaust gas in the cooling system.
Has Car Mechanics reviewed any sealants, and published comments on their effectiveness, or otherwise? I have 10 years of CM issues, but my index system is lacking. Oh, for a master index, if there be such a thing!
David Born
A I can first say that you will find an index of the past year’s magazines printed annually in the back of the January or February edition each year – this hopefully should assist in your search for future articles.
With regard to the sealants it does not seem that we have specifically covered the efficiency of sealants for some time. There is though one sealant that I have been using for over forty years and would never hesitate to recommend – that is Wellseal Jointing Compound. Wellseal was originally developed by Rolls Royce Ltd and is now manufactured under license. It is a unique sticky brown compound and is non-hardening. It is also highly resistant to lubricants and coolants and is non-corrosive.
I grew up using Wellseal to assemble engines of all shapes and sizes and it is still my top go to product. Find it here: https://bit.ly/CMIVwjc
The main reason for this may be that if the airbag were to be triggered by a rouge system, it would be better to have the airbag triggered when the battery was connected and the vehicle unoccupied than when the ignition was first switched on when sitting in the vehicle. There are actually further instructions for vehicles equipped with push-button start and keyless ignition systems, where the ignition cannot be left on when connecting the battery, that when starting the vehicle the seat should be in the rearmost position. This is also to mitigate any possible injury from an airbag inflation.
SAAB 9-3
Power drain
Q I have a 2005 Saab 9-3 1.9 8v TiD. A few weeks ago, the 12-monthold battery was completely dead. I put on a spare battery while the original was recharging, but that went totally flat after two days, as did the original battery after being fully charged.
Investigation revealed that I have a power drain of just over 3 amps with nothing switched on or running. I have traced it to the 20-amp fuse F14, labelled Audio Infotainment Control Panel in the fusebox on the passenger side of the dashboard. Pulling this out fixed the power drain and the car still runs perfectly fine after removing the fuse, apart from losing the display on the infotainment display, radio CD, aircon and the audible indicator clicker. The circuit diagram in the Haynes manual does not show any connection to either the aircon or indicator.
While I can obviously drive the car by replacing the fuse every time I go out and removing it on returning home, it is a bit of a pain. Is there a better solution?
Brian Salisbury
A The circuit details indicate that fuse F14 supplies only the radio head unit and the infotainment control panel. This is a constant feed from the battery and would cause the battery to drain if there was a fault present in this circuit. Like you, I can see no connection between this fuse and the aircon.
One of the units that does commonly have issues on your vehicle is the amplifier for the audio system, which should be located under the seat; disconnecting this may help narrow down the source of the drain. Another unit that regularly gives problems is the CIM (Column Integrated Module), which would affect the audible indicator. Assuming you have steering wheel controls, this would also have a connection with the infotainment centre.
The complexities of modern vehicle electronics can make diagnosis of such very difficult. If the drain cannot be narrowed down by disconnecting the amplifier, it may require the vehicle to be connected to a Tech2 system to correctly identify the
