Just had my windows tinted, so the cars been sat on the drive, stop/start etc. the guy at Tintsmart has done a cracking job, but upon starting the car I noticed the airbag light illuminated (along with the small button next to it). Through the process of elimination I've found the following:

When I get in the car I can hear a relay clicking somewhere passenger side dash
If I turn the passenger airbag off, the clicking stops.
With the key in position II, the airbag dash light illuminates whether the airbag is turned on or off

So I'm guessing that the airbag fuse has gone, or the battery is low so I'm getting spurious errors. It could be the latter as I've been away for 10 days and only done a short run + the ACC light/button coming on doesn't make sense unless fed by the same fuse, but unlikely?

Any ideas? I haven't located the fuse box and had a look yet? 2010 TDV8...

If the guys fitting the tints spent a few hours with the doors opening and closing then the interior lights would have been on quite a lot of the time and if they were playing the radio at the same time the battery may have been drained. Have you bought yourself a CTEK battery charger yet? I bought a MXS 5.0 last year and it is really great. Put the battery on charge and see if everything is resolved. If it happens again you might need to check the battery drain - all you need is a multimeter (Screwfix sell a good value one ) 2008 MY Java Black TDV8 HSE

Hi Paddi, the guy only spent a couple of hours, but ran the car abit in idle also. I've had 1 short run in 2weeks and the fact the ACC warning switch (next to door lock/unlock) comes on points to battery. Will have a look at one of those chargers tomorrow, nice 200 mile run on Saturday should help!  2010 TDV8...

Went out this morning & got a charger, turned the passenger airbag off, but the light illuminates all the time & the ACC triangle button flashes when ignition on stage II. Got the low power warning when turning the stereo above 20 (test ) so looks like it's the battery giving spurios issues.

Anyway, back home now, plugged in the charger & was showing low at 13.1V so now trickle charging...

What should the battery voltage be, around 14.4? 2010 TDV8...

Hi,
You don't say what sort of charger you are using but the voltage should be checked when the car hasn't been started for a couple of hours or so and if testing after charging; again you should leave it a few hours before checking the voltage.
The radio always gives the low power mode message when the engine is switched off.

Here is a rough guide showing voltage to state of charge:


The open circuit voltage, is measured when the engine is off and no loads are connected. It can be approximately related to the charge of the battery by:

Open circuit voltage Approximate charge Relative acid density
12 V
12.60 V 100% 1.265 g/cm3
12.35 V 75% 1.225 g/cm3
12.10 V 50% 1.190 g/cm3
11.95 V 25% 1.155 g/cm3
11.70 V 0% 1.120 g/cm3
Open circuit voltage is also affected by temperature, and the specific gravity of the electrolyte at full charge.

The following is common for a six-cell automotive lead-acid battery at room temperature:

Quiescent (open-circuit) voltage at full charge: 12.6 V
Fully discharged: 11.8 V
Charge with 13.2–14.4 V
Gassing voltage: 14.4 V
Continuous-preservation charge with max. 13.2 V
After full charge the terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V
Open circuit voltage is measured 12 hours after charging to allow surface charge to dissipate and enable a more accurate reading.
All voltages are at 20 °C, and must be adjusted -0.022V/°C for temperature changes (negative temperature coefficient - lower voltage at higher temperature).

None of the above tests the cranking power of the battery but as you have a new battery that shouldn't be an issue for yours? 2008 MY Java Black TDV8 HSE

Hi Paddi,

I'm using a RING Smartcharge +12 and didn't have the kit to check the voltage first thing but must have been <13 as the radio waring was with engine on, but was OK by the time I'd made a 10mile round trip & showing 13.1V.

My new shiny RING charger shows the following messages;

LO when <13>13.5V
70% charged >13.8V
80% charged >14.0V
90% charged >=14.2V
FULL when reaches flost charge point.

After 2 hrs, mine's showing 14.4V 90% and the amperage is reducing down (from 1.8 initially to 0.9) so I guess it's going through the final cycle to achieve full charge. I guess my question is, would I expect electrical gremlins at <13.0V, me thinks yes, but yet to check out Airbag light...

Cranking power is fine, just a tad sluggish at -4C this morning with <13V

Just unlocked it again & battery charger dropped to 13.3V and LO warning on the charger, but sat nav & lights fired up but confusing me....

... now shot back up to 14.4V in 5 mins, I guess unlocking the car fires up alot of kit, still chrging though until the charger says it's finished. 2010 TDV8...

Last edited by 57TDV8 on Thu Mar 14 2013 8:20pm. Edited 1 time in total

It looks as if the voltages you are seeing simply reflect the voltage being used by the charger at different stages of the cycle. i.e. they only indirectly represent the stage of charge of the battery.

The only way you will really know is by applying a multimeter to the battery after it has been fully charged and then left overnight to stabilise.

Can't help you with the airbag light issue unless it is supposed to light up when it is turned off as a warning (kind of makes sense).

By the way - I wouldn't think it is a good idea to mess with unlocking the car and putting the key in whilst the battery is charging; better to let the cahrger do its thing whilst the car is 'asleep'. 2008 MY Java Black TDV8 HSE

Cheers Paddi,

There's a built in multi-meter so will charge until about 4pm, then check in the morning.

The airbag light should be on at stage II ignition only showing it's been turned off, but is illuminated all the time (when driving), when I turn it off, lights still on while driving, but relay clicking stops, so I'm guessing a blown fuse which low voltage issues may have contributed to?

Will see when I fire her up this afternoon, appreciate your help!  2010 TDV8...

All fixed now with a good charge, no airbag or ACC button errors  2010 TDV8...

as kav would say -'another small but significant victory for the DIY brigade' 2008 MY Java Black TDV8 HSE