2/24/ K Excessive Parasitic Draw? Check If the B-CAN System Is Awake 2006 Honda Ridgeline MotoLogic. ServiceNews Article

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1 ServiceNews Article July 2008 Helping you fix it right the first time - every time Excessive Parasitic Draw? Check If the B-CAN System Is Awake Currently Applies To: All models equipped with the B-CAN system When it comes to parasitic draw, the body controller area network (B-CAN) system first introduced in the 03 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 you 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. Just remember if the draw is less than 50 ma, it s normal; if it s 50 ma or more, it s excessive. 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. Don t Just Rely on Component Replacement Many service techs replace B-CAN-related components because they think those components are causing the excessive parasitic draw. When checking for excessive draw, they 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. So the bottom line is this: When it comes to excessive parasitic draw, you can t rely on component replacement to always fix things. Even though the suspected component was replaced, there s still an excessive parasitic draw problem that will probably wind up in a comeback... not to mention one very unhappy service customer. Narrowing Things Down An easy way to find out if the B-CAN system is staying awake and causing an excessive parasitic draw problem is to momentarily short one B-CAN communication wire to ground. There are two types of B-CAN systems: a slower (33.33 kbps) single-wire system, and a faster (125 kbps) two-wire system, which was first introduced in the 08 Accord. Shorting the single wire to ground (single-wire system) or the CAN_H wire to ground (two-wire system) at any of the B-CAN-related components stops all B-CAN communication and puts all of the control units into the sleep mode. If doing this gets rid of the excessive parasitic draw, then an input signal to one of the control units or a control unit itself is keeping the system awake. 2/7

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3 ServiceNews Article Helping you fix it right the first time - every time Finding the Culprit There are two ways to find out which control unit is keeping the B-CAN system awake. One way is to use the All Data List in the HDS to check for any abnormal switch inputs such as a door lock switch that stays on. Such inputs will keep the system awake. The other way is to start unplugging the components on the B-CAN circuit one at a time. When you unplug the suspected control unit, the rest of the B-CAN-related components will fall sleep. Make sure there are no abnormal switch inputs to that control unit, though, such as a door lock switch that stays on, otherwise the B-CAN system will stay awake. Some Handy Tips Without a doubt, chasing down an excessive parasitic draw problem can be time-consuming, even frustrating work. Here are some handy tips to help make that job go just a little easier: Use the Auto Battery/Electrical System Analyzer (ED-18) to make sure the vehicle s battery and charging system are OK. Check to see if the vehicle has any aftermarket accessories. If it does, let the service advisor know right away. He or she will need to get permission from your customer before you can unplug or remove those accessories. If the vehicle has a security system, make sure you unplug the hood switch to simulate a closed hood. To check for excessive parasitic draw, use the LH41A AC/DC Low Current Clamp Meter (Model No. FLULH41A), a required special tool. Only clamp meters that match the LH41A s resolution and accuracy specs can be used to measure parasitic draw. See Meet the LH41A Clamp Meter! below for details. Check the vehicle under the same conditions reported by your customer or written on the RO (for example, your customer reported all the doors were locked and the security system was turned on). After turning the ignition switch to LOCK (0), open and close the driver s door to shut off the key-off timer. On most vehicles, this will cut the time it takes for the B-CAN system to go into the sleep mode. Meet the LH41A Clamp Meter! Most clamp meters can t check for excessive parasitic draw because they won t detect the small electrical fields that parasitic draw generates. Also, the jaws on many of these clamp meters are just too small to fit over battery cables, making them unusable for this job. This is where the LH41A clamp meter comes in. This required special tool has several important operating features: 4/7

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5 ServiceNews Article Helping you fix it right the first time - every time Zero Adjustment: The LH41A is really sensitive to magnetic fields and can change readings when you move it. When doing a zero adjustment, hold the tool near the battery negative cable in the same position you ll be using it during testing. Make sure the jaws are closed and press the AUTO ZERO button. Power Switch: The LH41A has a three-position power switch: OFF HOLD, DC, and AC. Always slide the switch to DC when you re checking parasitic draw. Auto Power Off: With the power switch set to DC, the LH41A will power down after about 8 minutes of inactivity. Data Hold: Sliding the power switch to OFF HOLD activates a data hold mode that displays the last measured value for about 10 seconds. Once that time is up, the LH41A powers down. Auto Ranging: The LH41A has two available ranges: 4 amp and 40 amp. Use the decimal position in the display to determine what range you re in. 4 amp: X.XXX or.xxxx 40 amp: XX.XX If you need to order more of these tools for your shop, give the Honda Tool and Equipment folks a call at You can also order it online; it s just a few clicks away on the in. From the main menu, click on SERVICE. You can then click on either Service Bay and Tool and Equipment Program or emall and Tool & Equipment. Either way takes you to the Tool and Equipment Program webpage. Once there, click on Online Catalog, enter the part number in the Search box, and click on Go!. You re taken straight to the order page. To Learn More... Want to sharpen your knowledge and skills on parasitic draw? Visit Online University, and check out skill module ELS60 - Key-off Draw Testing. 6/7

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