Parasitic battery drain
Thread Starter
Joined: Mar 2015
Posts: 3
Parasitic battery drain
Firstly I note that this forum is very Americas-centric so please note that this thread is from the UK, and I am unsure if there are any significant specification differences between UK and USA/Canada models.
My wife's vehicle has covered about 20,000 miles. It was initially used from new by a Honda manager as his company car from September 2010, we bought it as an "ex-demonstrater" in January 2011. For our first 3 years mileage was mostly on long journeys. During the 3 year warranty period, the car once failed to start. Honda (free of charge) sent out the Automobile Association who pronounced it "nothing wrong". This last year the car has done very little mileage, in repeated short journeys - regularly fails to start. Battery is OK, and alternator is OK, so there is a parasitic battery drain. Auto electricians charge UKŁ60 per hour, so I have done as much diagnosis as I am able. The drain with everything turned off and key out is 380 milliamps, should be no more than about 50ma. Removing the under-bonnet (hood!) fuse number 15 stops the parasitic drain - draw drops to 60ma. Incidentally the manual says the fuse is 7.5a, but actually it is a 10a fuse in that slot. The fuse is called "Back Up". So what is my next step regarding checking for components that are causing the drain, i.e. what components are protected by 10a fuse number 15?
Sorry for such a long post, but I read the rule which said "tell the whole story"
Honda Accord Tourer 2.0 i-vtec auto transmission UK 2009 model, first registered September 2010.
My wife's vehicle has covered about 20,000 miles. It was initially used from new by a Honda manager as his company car from September 2010, we bought it as an "ex-demonstrater" in January 2011. For our first 3 years mileage was mostly on long journeys. During the 3 year warranty period, the car once failed to start. Honda (free of charge) sent out the Automobile Association who pronounced it "nothing wrong". This last year the car has done very little mileage, in repeated short journeys - regularly fails to start. Battery is OK, and alternator is OK, so there is a parasitic battery drain. Auto electricians charge UKŁ60 per hour, so I have done as much diagnosis as I am able. The drain with everything turned off and key out is 380 milliamps, should be no more than about 50ma. Removing the under-bonnet (hood!) fuse number 15 stops the parasitic drain - draw drops to 60ma. Incidentally the manual says the fuse is 7.5a, but actually it is a 10a fuse in that slot. The fuse is called "Back Up". So what is my next step regarding checking for components that are causing the drain, i.e. what components are protected by 10a fuse number 15?
Sorry for such a long post, but I read the rule which said "tell the whole story"
Honda Accord Tourer 2.0 i-vtec auto transmission UK 2009 model, first registered September 2010.
Senior Member
Joined: Mar 2014
Posts: 595
I am not exactly sure where to start here, but with the car off I would take a test light or multimeter and check all the fuses. If you get a reading at a fuse that should be dead then that may be the circuit where you are getting the draw. I love the challenge of working on these types of problems in a shop setting, but doing it over the Internet can be almost impossible. Welcome to HAF. We are here to help.
Super Moderator
Joined: May 2006
Posts: 18,398
From: Wisconsin
When looking at current draw when it's shut down, it's important to wait long enough for some systems to "shut down".
Your car is new-enough to have some electronic systems that are still powered up for maybe a couple minutes after you "shut down" the car. Theft alarms, timers for door-locking, other silly things like that. Your 380ma draw might drop way down after a couple minutes, so your problem might not be on that circuit but somewhere else you haven't looked.
Your car is new-enough to have some electronic systems that are still powered up for maybe a couple minutes after you "shut down" the car. Theft alarms, timers for door-locking, other silly things like that. Your 380ma draw might drop way down after a couple minutes, so your problem might not be on that circuit but somewhere else you haven't looked.
Super Moderator
Joined: Oct 2010
Posts: 7,099
From: United States
Not sure what components are protected by Fuse No. 15 on your UK model, as the circuits are probably a little different than North American models. We don't have a Tourer model.
Here’s part of some info. on parasitic draw applicable to many of the newer Hondas:
When it comes to parasitic draw, the body controller area network (B-CAN) system—first introduced in the 2003 Accord—is a major contributor. With the ignition switch turned to LOCK (0), all B-CAN-related components still receive battery power. This gives the various control units such as the gauge control module, the multiplex integrated control unit (MICU), the door multiplex control unit, the climate control unit, the power seat control unit, etc., a means of communicating when, for instance, a power door lock switch input signal changes or there’s a signal received from a keyless remote transmitter. Knowing what the B-CAN system does when you turn the ignition switch to LOCK (0) will help to recognize if it’s causing an excessive parasitic draw problem. Normal parasitic draw on a battery varies from model to model, depending on the number of control units involved. If the draw is less than 50 mA, it’s normal; if it’s 50 mA or more, it’s excessive. Excessive draw may be from B-CAN system staying awake.
Wake-up Mode and Sleep Mode
The B-CAN system has two operating modes to reduce parasitic draw: the wake-up mode and the sleep mode. With the ignition switch turned to ON (II), the system is in the wake-up mode. During this time, the system has both +B power (HOT AT ALL TIMES) and IG1 power (HOT WITH IGNITION SWITCH ON) and there’s a parasitic draw on the battery of about 200 mA or more. When you turn the ignition switch to LOCK (0), the system stays awake as long as the key-off timer (part of the MICU) is running. The key-off timer shuts off when the B-CAN system receives a door switch open input signal; otherwise, it shuts off right at 10 minutes. With the system now in the sleep mode, the parasitic draw on the battery drops to less than 50 mA. It still has +B power (HOT AT ALL TIMES), though, and there are a number of signal inputs that can wake it up to do some work. A good example is the power door lock switch. When you push the switch to its lock or unlock position, the system wakes up, does whatever it needs to do, and then goes back to sleep 5 seconds later.
Checking for excessive draw:
When checking for excessive draw, many techs find that by pulling the backup fuse to the MICU, the parasitic draw drops to normal. What they don’t realize, though, is that the real cause for the B-CAN system staying awake could be a stuck door lock switch. If that door lock switch sticks in either its lock or unlock position (the input signal stays on), the system won’t return to the sleep mode. This will keep an excessive parasitic draw on the battery that will kill it in short order. Just how long that actually takes depends on the battery’s state of charge and other variables. A parasitic draw of about 200 mA will usually kill a battery in about 2 days.
Here’s part of some info. on parasitic draw applicable to many of the newer Hondas:
When it comes to parasitic draw, the body controller area network (B-CAN) system—first introduced in the 2003 Accord—is a major contributor. With the ignition switch turned to LOCK (0), all B-CAN-related components still receive battery power. This gives the various control units such as the gauge control module, the multiplex integrated control unit (MICU), the door multiplex control unit, the climate control unit, the power seat control unit, etc., a means of communicating when, for instance, a power door lock switch input signal changes or there’s a signal received from a keyless remote transmitter. Knowing what the B-CAN system does when you turn the ignition switch to LOCK (0) will help to recognize if it’s causing an excessive parasitic draw problem. Normal parasitic draw on a battery varies from model to model, depending on the number of control units involved. If the draw is less than 50 mA, it’s normal; if it’s 50 mA or more, it’s excessive. Excessive draw may be from B-CAN system staying awake.
Wake-up Mode and Sleep Mode
The B-CAN system has two operating modes to reduce parasitic draw: the wake-up mode and the sleep mode. With the ignition switch turned to ON (II), the system is in the wake-up mode. During this time, the system has both +B power (HOT AT ALL TIMES) and IG1 power (HOT WITH IGNITION SWITCH ON) and there’s a parasitic draw on the battery of about 200 mA or more. When you turn the ignition switch to LOCK (0), the system stays awake as long as the key-off timer (part of the MICU) is running. The key-off timer shuts off when the B-CAN system receives a door switch open input signal; otherwise, it shuts off right at 10 minutes. With the system now in the sleep mode, the parasitic draw on the battery drops to less than 50 mA. It still has +B power (HOT AT ALL TIMES), though, and there are a number of signal inputs that can wake it up to do some work. A good example is the power door lock switch. When you push the switch to its lock or unlock position, the system wakes up, does whatever it needs to do, and then goes back to sleep 5 seconds later.
Checking for excessive draw:
When checking for excessive draw, many techs find that by pulling the backup fuse to the MICU, the parasitic draw drops to normal. What they don’t realize, though, is that the real cause for the B-CAN system staying awake could be a stuck door lock switch. If that door lock switch sticks in either its lock or unlock position (the input signal stays on), the system won’t return to the sleep mode. This will keep an excessive parasitic draw on the battery that will kill it in short order. Just how long that actually takes depends on the battery’s state of charge and other variables. A parasitic draw of about 200 mA will usually kill a battery in about 2 days.
Thread Starter
Joined: Mar 2015
Posts: 3
Thanks to Turtlehead, JimBlake and Redbull-1 for responding, especially Redbull-1 for fantastic level of detail. So for me its back to pulling ALL fuses, rather than stopping with triumphant glee at the first one to to give a result. I hate electrics! Give me something mechanical to play with and I'm happy. After one more go, I think it will be back in the shop. Cheers,
Steve.
Steve.
Super Moderator
Joined: Oct 2010
Posts: 7,099
From: United States
It does not necessarily mean you have to pull more fuses. If the parasitic draw drops to normal after pulling that fuse, then you would start checking other component/circuits protected by the same fuse. With the fuse re-installed, you can test individual component/circuits.
For example, you can individually unplug connectors or test wiring for shorts with a meter.
This image is just an example of one connector on a U.S. Accord 2009-2012. This is the door lock actuator/**** switch that is normally plugged into the door lock actuator.
For example, you can individually unplug connectors or test wiring for shorts with a meter.
This image is just an example of one connector on a U.S. Accord 2009-2012. This is the door lock actuator/**** switch that is normally plugged into the door lock actuator.
Super Moderator
Joined: Oct 2010
Posts: 7,099
From: United States
On the U.S. models, under-hood BACK-UP fuse no. 15 (10A) would protect the following components or circuits:
Audio Unit, Audio-HVAC Sub Display Unit, DLC, Driver’s Door Courtesy Light(4-door), Driver’s MICU, Front Passenger’s Door Courtesy Light (4-door), Fuse 5 inPassenger’s Under-dash Fuse/Relay Box, Gauge Control Module, HandsFreeLinkControl Unit (Navigation), Immobilizer-Keyless Control Unit, Microphone(Navigation), Navigation Display Unit (Navigation), Navigation Unit (Navigation),Passenger’s MICU, Power Window Master Switch
Audio Unit, Audio-HVAC Sub Display Unit, DLC, Driver’s Door Courtesy Light(4-door), Driver’s MICU, Front Passenger’s Door Courtesy Light (4-door), Fuse 5 inPassenger’s Under-dash Fuse/Relay Box, Gauge Control Module, HandsFreeLinkControl Unit (Navigation), Immobilizer-Keyless Control Unit, Microphone(Navigation), Navigation Display Unit (Navigation), Navigation Unit (Navigation),Passenger’s MICU, Power Window Master Switch
Last edited by redbull-1; Mar 4, 2015 at 11:41 PM.
Thread Starter
Joined: Mar 2015
Posts: 3
Parasitic drain fixed
Once again many thanks for the helpful responses. In gratitude I would like to close with the end result for this vehicle. Having identified the circuit causing the problem (engine bay fuse number 15) Honda UK Customer Service refused to assist by listing for me all of the components in that circuit, which would have given me the opportunity to check further. Obviously Honda's motivation was to keep me in the dealer network, so having stonewalled me I had to relent. I have to admit the service was excellent - the problem was caused by the hands-free telephone unit - which we have never used. I agreed that Honda should leave it disconnected, as we never use a phone in the car. They only charged 30 minutes labour (UKsterling 49.50) and it was that quick because they went straight to that component without looking anywhere else. In other words it was a problem known to Honda - although the technician said it was common on Civics, but not common on my Accord model. So after some aggravation, back on the road.
Joined: Feb 2020
Posts: 1
2009 Honda Accord EXL
My car constantly dies, the battery tests out good. My brother who is a mechanic said there is a draw in the system. It seems like it happens when the vehicle is started and than shut off when it's moved for a short distance. Any ideas in regards to what could be causing the amp draw?
