Afternoon peeps,

I'm having a little trouble with severe battery drain at the minute and when I plug into allcomms I'm getting a CAN bus Fault appearing in the Air Suspension unit.

Does anyone know what this means and if there's a cure? I'm thinking that it's possibly connected to my battery drain??

The CANbus is the data network that ties the cars automotive functions together i.e. all the stuff the car relies on to make it move - ABS, Suspension, Gearbox, Transfer Box, Engine etc....

The way the data works is a packet of information is sent that has a header which says which ECU the information is intended for. Each ECU picks up the packet, reads the header and decides if the information is for them, if it is, it reads it and passes it on, if not it just pushes along down the line to the next ECU in turn...

As an Example, the Dynamic Stability Control system (which is controled via the ABS ECU) relies on information from the EAS system to tell it the current height and attitude of the vehicle, this is combined with the information it received from the Yaw Sensor and the Road speed information from the ABS system.

If you have an ABS sensor failure, it will also render the EAS system inoperative, as the system communicate along the CANbus....

If you know your EAS is working correctly and you have no other faults, I would say it is just the CANbus hiccuping as it has received some odd packets of data along the way....that being said, the Twisted Pair of cables that make up the CANbus have been known corrode at the odd ECU connection, maybe looking at the ABS ECU plug, the EAS ECU plug and etc just to make sure. but the CANbus itself won't cause a massive battery drain I wouldn't think as it is only a data network running at the very most 5V signal at milliamps if anything.

I would be tempted to look at the Final Stage Resistor, the Headlamps Wipers or the ignition switch.

Also using a fuse amp meter thingy (one where you can remove a fuse and place this meter in place of the fuse) to see if you can narrow down which circuit it is coming from.

Saint thanks so much for the lesson there that's an amazing response.

I'm currently sat in the car with a fuse testing things and I'm currently logged in to fuse 12 for the Air Conditioner, front seat heating.

When I took the fuse out the fan in the HVAC stopped so I plugged in my gadget and locked the car with the remote and these are my findings so far....

Fuse 12 draining 1.92a when unlocking and locking then
1.89 after 2 minutes
1.60 after 6 minutes right up to 18 minutes
0.00 at 18 minutes right through until 35 minutes.
Unlocked car and jumps to 2.60 then settles at 1.80 after few seconds.

Also I have the final stage resistor unplugged and the nave system is reading 0.00a as I tested this earlier.

Do you think the above readings are high??

Is there a fuse for the ignition switch?

I've checked the fuse for headlight cleaning that's reading 0.00 and windscreen wiper system also reading 0.00.

Well bloody car is now dead as a fox that's been smashed in by a range rover!!!

Been outside with it running for agessssss and left the air conditioner fuse out as that seemed to be the only thing that was drawing quite a bit of power. Locked the car with the key fob came inside for a cup of tea and went back out 35 minutes later to find it dead.

Could it be the battery? I've been disconnecting the battery every time I park up recently and when I reconnect it the car always starts so I'm thinking the battery isn't losing any power by itself when it's disconnected.

I have a suspicion it could be the Alternator....

If it has run flat, then the Alternator hasn't been charging the battery properly...and if the rectifier pack is knackered, it can allow the battery to drain through the Alternator...

Saint.V8 said:

I have a suspicion it could be the Alternator....

If it has run flat, then the Alternator hasn't been charging the battery properly...and if the rectifier pack is knackered, it can allow the battery to drain through the Alternator...

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That's a good shout but also a sick battery can rapidly go flat with just a few milliamps drain.

I'm getting 14 volts when it's running so the alternator is charging the battery but how do I check to see if it's going the other way?

I've just spent 130 quid on a new battery due to the nice man giving me a hefty discount. I'm going to take my old battery into him and get it checked. I've just put a volt meter on it and it's reading 12.3 volts????????

Pgups said:

I'm getting 14 volts when it's running so the alternator is charging the battery but how do I check to see if it's going the other way?

I've just spent 130 quid on a new battery due to the nice man giving me a hefty discount. I'm going to take my old battery into him and get it checked. I've just put a volt meter on it and it's reading 12.3 volts????????

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Voltage off load is not a good indication of battery condition.

I was getting a canbus fault on my eas when I had leaky airbags but my front suspension was totally shot. When I replaced it the canbus error went away. I spoke to storey at all comms and he said you can also get a canbus error until you reset the steering angle by turning the steering wheel lock to lockI bought an optimate 6 charger instead of a new battery when mine kept going flat and it was fine after I ran it through the rescue cycle.
You can leave it connected if you like but if you have an underlying problem it won't help.
As saint said I read loads about the resistor behind the dash causing problems
The only good thing on my car is the battery...

Well the new battery has been on the car since Monday and so far so good it's not dead. I still have the hvac disconnected via the fuse so I'll reconnect that today and see what happens. Fingers crossed it was just a knackered battery.

what used to drain mine was leaving it unlocked while working on it as i dont think it really goes to sleep unless its locked via the key fob

That's a good point. It prob does go to sleep eventually but if you have to open a door for anything it will just wake up for another 20 mins.

Could connect a jump pack while working on it or if you don't need power take the neg terminal off.

Pgups said:

That's a good point. It prob does go to sleep eventually but if you have to open a door for anything it will just wake up for another 20 mins.

Could connect a jump pack while working on it or if you don't need power take the neg terminal off.

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i dont touch my battery if i can help it, i learnt by disconnecting the battery without waiting for it to shut itself down and wiped the engine / immobiliser link which meant a car transporter to the main dealer to get it reprogrammed.. happy days
i can leave the optimate connected though which would help, they really are a good piece of kit
i was only really getting a problem before i used the optimate to recon the battery when i was working on it more than driving it, well like now really

Pgups said:

That's a good point. It prob does go to sleep eventually but if you have to open a door for anything it will just wake up for another 20 mins.

Could connect a jump pack while working on it or if you don't need power take the neg terminal off.

Click to expand...

At our Archery field, I leave mine unlocked and the tail gate open most of the evening (in the summer this would be from 4.30pm till just after 10pm) never had a battery drain issue with doing that!