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Robbie's Guide For Battery & Quiescent Drain Testing
Robbie's Guide For Battery & Quiescent Drain Testing
1. Always start from a known good point with a charged battery. Please note that batteries can fail and self-discharge internally or even from crud spanning the gap between the terminals. Battery terminal connections should be pushed down the tapered terminal before tightening to ensure a good connection. All aftermarket electrical systems should be disconnected or isolated before testing. Do not convince yourself that the aftermarket kit was 'ok before so therefore it should be ok now'. No exceptions, disconnect it.
a. Good battery voltage:
Click image to enlarge
2. The vehicle has to be asleep before testing, so open the bonnet, short the bonnet sensor under the RHS latch and either lock the vehicle or mechanically latch the doors open so that the vehicle thinks they are closed. If you are fooling the locks don't set the internal alarm. Even when asleep the alarm LED flashes, which is detectable, and the EAS and potentially the EPB can occasionally draw power.
a. Bonnet latch connector with paperclip:
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b. Depending on vehicle, Model Year and specification it can take a while for the vehicle to sleep:
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3. The preferred method is to use a DC capable current clamp that has a milliamp range with a 1mA resolution. This can be clamped on individual circuits or groups of circuits. It is easier to start with large groups (such as the BJB) before delving into individual circuits. It is not possible to remove fuses as part of the diagnostics as this may wake systems or stop others from sleeping which will make nonsense of the diagnostics. Equally, if the drain is caused by an energised relay you may reset it by pulling the fuse and lose the very thing you are looking for.
a. Current clamp for attaching to DMM:
Click image to enlarge
4. At the +ve terminal the load paths split into 2 directions; one towards the starter/alternator and the other to the battery junction box (BJB). These should be tested individually. Start with the alternator cable; there should be no current running down this lead in this state. Be aware that some alternator failures that can leak current only do so when either cold or hot, so even if you have zero current flow you may have to come back to this if no other faults are found.
5. The main positive lead from the battery to the BJB can be gently manoeuvred upwards to allow for an amp clamp. You should detect a current less than the value shown in the previous table. As an example an older D3 with no TMPS and no tracker fitted should be below 22mA. My own MY13 D4 should be below 30mA, as shown below:
Click image to enlarge
a. Due to the alarm etc the figure can move around a bit, up to 26mA in my case, but this is still below the 30mA maximum:
Click image to enlarge
6. If you do have a drain beyond the table limit you have to move systematically through all the various circuits to find out which are drawing more than they should. To save time you can quickly trace down all the fuses with a test light or digital multimeter (DMM) to see which circuits have zero power on them. This allows you to focus on the circuits that have some power on them.
7. You have a few options for testing individual circuits. The workshop method is to release the BJB and clamp the wires from below. This does work but the looms on some later vehicles can be a bit tight. A method I like is to use is via the test points on the back of the blade fuses and effectively treat the fuse as a resister of known value (as that is what they are) and Ohms law to deduce the current flow by measuring the voltage drop in mV and using a calculator or a look-up table to find the actual current flow.
a. The tables are in my gallery and look like this:
Click image to enlarge
b. The fuse test points if you have never really noticed them before look like this and can be tested thus:
Click image to enlarge
c. For those that like maths rather than the table the current calculation on this circuit (fuel pump) was:
25 Amp Fuse = 2.36 mOhm or 0.00236 Ohms
Measured @ 0.0235 V or 23.5 mV
= 9.95763 Amps
8. If you do not fancy using a clamp from below or using the voltage drop method you can use a fuse buddy or a home made fly lead to form a wire loop that can be either inserted directly into a DMM (if the circuit is below the fuse limit of the DMM) or to clamp with a DC clamp. There are bespoke kits on the market for those that like to spend money but you can make your own fly lead with spade crimps or get one of these and link it together with a female to female banana plug:
Click image to enlarge
a. Same circuit again from the example above, producing very similar results to the voltage drop method:
Click image to enlarge
Click image to enlarge
9. The method above is also useful for very low power circuits as you can wind the wire around the clamp a few times for extra accuracy and divide the number displayed by the number of times you have wound the wire through the jaws of the amp clamp.
10. Current can be measured anywhere on the circuit so in practice you can clamp anywhere with access. This can be helpful when you are down at the component level but a great deal of diagnostics can be done at the BJB or CJB.
11. It is not a complicated thing to do and definitely something you would want to do DIY as it takes time and patience. Even if you have no idea how to fix the problem circuit (although the forum is pretty good) it will save a bundle of cash if you have done the time consuming diagnostics to narrow it down to a particular circuit. Before you know it your workbench or kitchen table looks like this and at least gives the illusion that you know what you are doing:
Click image to enlarge
A bit of a long post so I hope this helps and I am always happy to help forum members, especially those willing to give it a go themselves. There are many ways to skin this particular cat so I am sure other members will have their own top-tips.
Land Rover - Turning Drivers into Mechanics Since 1948
Last edited by Robbie on 1st Apr 2015 9:28 am. Edited 1 time in total
30th Oct 2014 4:19 pm
Robbie
Member Since: 05 Feb 2006
Location: ¯\_(ツ)_/¯
Posts: 17932
A real-world example using an MY08 D3
1. This particular vehicle would consistently demonstrate the symptoms of a quiescent battery drain when left for a number of days. The alternator was relatively new, as was the battery. The vehicle was also equipped with a Traxide dual battery setup and a BAS FBHIC. As these are aftermarket accessories they were disconnected at the start of testing.
2. The main battery was tested when free of surface charge effects and measured 12.6v - a healthy figure. The alternator was also tested with a DMM at 13.9v, with the ECM voltage reporting at 13.8v. With an outside air temp of 10 deg C the alternator output suggested that the ECM was controlling the alternator and producing a 'float' charge only. As the vehicle had just been driven 70 miles this was to be expected. Below is the alternator output as displayed on the IIDTool (the red trace), with the standard alternator charging figures per temperature listed on the table below:
Click image to enlarge
Click image to enlarge
3. Whilst far from essential, fault code readings can be helpful when diagnosing a quiescent drain as it may give a clue as to any misbehaving ECUs. The results have to be treated with caution so they are just something to be born in mind. In this particular case the fault codes were unremarkable and mainly reflected issues caused by previous battery disconnects. These codes were recorded then all reset to form a new baseline. No codes reappeared on restart, indicative of no major issues. As good power and ground connections are critical these were all checked with a DMM, including the second battery and Traxide cables. Again, the results were unremarkable.
4. With the Traxide dual battery and the BAS FBHIC disconnected the first thing tested was the alternator cable - this showed zero drain (at least with everything warm). With the bonnet open, the sensor disabled and the vehicle locked, the vehicle took just over 30 mins to go to sleep. In this state the current carried by the main battery to the Battery Junction Box (BJB) was 125mA or more. The current cycled upwards in time with the alarm LED flash:
Click image to enlarge
5. The owner had previously observed some current flow in the internal lights so given this the initial focus was on the Body Control Module (BCM, part of the Central Junction Box) power feed, particularly link fuse 15E (40 amp) in the BJB:
Click image to enlarge
6. As this JCASE style of fuse (aka cartridge fuse or link fuse) has no test points I used a homemade fuse holder with crimped spade connectors to create a fused current loop. This way a DC amp clamp could be used without disassembling the BJB and clamping the wires from beneath. It showed around 22mA of current or so, but varied over time:
Click image to enlarge
7. As this current was pretty typical for the BCM in this state the search went broader and all fuses were checked with a test light (just visible in the photo above) to carefully and methodically confirm that those that should not have power did not and that those that should be powered did so. More detailed testing of mV via the fuse test pins and using the voltage drop tables showed that fuse 26E (20 amp) had more power running through it than you would expect. Fuse 26E feeds the EAS control module; this is the ECU that controls the air suspension:
Click image to enlarge
8. A fuse buddy was installed to form a loop in this mini blade fuse position so that the current could be monitored. Removing this fuse did not awaken the vehicle (which is a risk) but following an initial spike of 1.7 amps it did drop the total current draw considerably. When I was happy that the current draw would not threaten my DMM fuse I used the fuse buddy to wire directly to my Fluke DMM and used the DC clamp on the main BJB feed to take simultaneous readings:
Click image to enlarge
9. The results showed that EAS module was drawing 58mA or more and that it was considerably higher than this before the fuse was removed and replaced (which must have reset something), with the rest of the vehicle drawing about 26mA for a grand total of 84mA (as shown on the DC amp clamp).
10. Remember my mantra about disabling all aftermarket accessories? Well the discussion on the EAS circuit drawing power prompted the owner to remember his aftermarket EAS modifications that allow him to adjust air suspension heights via a switch. By the EPB is this additional control panel:
Click image to enlarge
11. The testing confirmed that the EAS Control Module circuit was drawing power when it should be in a suspended state. This could be a problem with the EAS module itself, its wiring or a wider system issue that is preventing it from sleeping. However, the prime suspect was the aftermarket modification; either by drawing power itself or by preventing the EAS from sleeping. The diagnostics took a few hours but this testing really is something that can be done DIY to avoid expensive dealer diagnostic time.
Added to Wiki.Land Rover - Turning Drivers into Mechanics Since 1948
Excellent post, thank you
Guess I'll be buying anamp clamp this evening ready to look for my battery drain this weekend!!!
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30th Oct 2014 5:15 pm
PatGAPInnov Site Sponsor
Member Since: 02 Dec 2011
Location: Montreal
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Good write up Robbie and explained well for the novice mechanic..
Flack
30th Oct 2014 7:14 pm
johnnychainsaw
Member Since: 24 Nov 2009
Location: West Sussex
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Nice one Robbie. Quality post
30th Oct 2014 7:32 pm
James W
Member Since: 27 Mar 2008
Location: Riyadh, KSA
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That was a pleasure to read. Good work Sir
30th Oct 2014 7:55 pm
Robbie
Member Since: 05 Feb 2006
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Posts: 17932
Thanks guys, very grateful for the praise and encouragement.
countrywide wrote:
Can you not let the car go to sleep unlocked and avoid the bonnet bypass etc?
Yep, the car should sleep with the doors unlocked and the revised (ie longer) times are in the table above. However, this would put the car in a different state to that most leave their car in; this may cloud the diagnostics and you could end up chasing your tail if the lock and sleep state influences the fault.
Opening unlocked doors also wakes things up and clearly you do not want interior lights coming on either. Locked or ideally 'faked' locked (so you can gain access if needed) is best. On D4s with keyless you need to keep the fob away from the vehicle too.Land Rover - Turning Drivers into Mechanics Since 1948
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