weak hybrid battery, hood switch mod.

[j91z28d1]

so I have seen this talked about but never actually done. so I decided to try it for a while and see how it works. I can say it works perfectly.

so back story for those they don't know. the main hybrid battery pack runs just about everything and gm designed the air cooling system badly, as in they didn't do anything to cool it at all. this is basically a prius pack with extra cells. Toyota put thought into the cooling on the prius and they go 200k on oem packs and will sell you a new one even today. gm did nothing but use the fan inside the case, and it slows down as the truck comes to a stop so you don't hear the fan running. our packs last 100k at best.. probably starting to give you issues by 80k.

so it's mostly impossible to buy a new pack from gm. the factory still exists, Toyota owns a part of it. which is the only reason they are still using nickel metal hydride technology, but anything you buy 3rd party like say green cubes is going to be battery's from junkyard cars run thru a referb process. I see as much as $4k for these packs.

signs of a weak hybrid pack, besides check engine light. is bucking as the engine starts when taking off from a stop sign, it's trying to drive the truck with one motor and start the engine with the other. if the pack is weak, the voltage crashes and the system shuts down, bucking and jerking.. I've seen posts when it's really bad it can try to Rev the engine to keep itself running, all while taking 2 feet on the brakes to keep it from driving thru stop signs. unstable voltage the other way can happen to, as when cells get weak and charged the voltage jumps up higher for the same current put in it. if this gets to the point that any one cell(2 modules) hits 20.4v for 4 seconds it will open the main contactors in the hybrid battery. at that point your whole truck shuts down, and since it's usually during braking, it's in the middle of traffic in rush hour. not fun. oddly it will usually throw a code for 42v lost to steering system when this happens, because technically it did, but because the hybrid cell over volt not a steering issue. which you'll need a tech 2 and scan thru the freeze frame data to find. usually this fixes itself as soon as you cycle the key and the voltage drops below 20.4. which it will. but it will get worse. point being these aren't really safe to just keep. driving on a dying pack.



so the hood switch trick is mainly for when your hybrid battery is weak and you don't want to buy a new one. side effect I found is it actually drives nicer and doesn't loose much mpg from not going into auto stop all the time.

I'll up load the diagram for anyone that wants to try it. the hood switch is wired so that the ecm knows if you just disconnect the plug, and throws a fault code. so you will have to jumper terminal a and d together(leaving be open) to tell it the hood is open when it's not.

I put a 3 way switch on mine, so I can flip it one way to work like normal, and the other way to bypass and tell the ecm it's open at all times. the plug is a few inches to the right of the hood latch as the easiest way to get to the wires.

can provide more info to anyone they needs it

 

[klaforte1]

@j91z28d1 Hi, can you send me more detailed info on this procedure. I recently bought a 2011 chevy silverado hybrid and would like to try this. My email is [email protected]. thanks!

 

[j91z28d1]

@j91z28d1 Hi, can you send me more detailed info on this procedure. I recently bought a 2011 chevy silverado hybrid and would like to try this. My email is [email protected]. thanks!

I'll send you an email tomorrow. in the mean time, you have any experience with wiring. like wiring in a switch. if so, super easy. if not, bit of a learning curve.

 

[klaforte1]

Yeah, I can wire in a switch.

 

[BG1988]

does remote startwork still i was able to get one cell from 98mAh to 900-950mAh...

 

[j91z28d1]

no sadly. remote start doesn't work.

you could put the switch inside the truck and turn it to normal the night before for cold starts and then switch back to open while driving to avoid all the bucking and bad stuff from a weak battery

 

[stiedemann]

Mike can you send me any details on this fix? I have a 2011 tahoe hybrid with 105k miles and now the battery pack is showing low voltage. I get the first start jerking motion. I plan to get a new Tahoe but want to keep this one until I get a new one so I need to buy a couple of months. You said you used a 3 postion switch, but you only listed normal and hood open. Can you explain? Also you said you keep it in normal at night then switch to hood open for driving. Does hood open still charge the hybrid battery when you are hitting the brakes?
Thanks,
Steve

 

[stiedemann]

Mike,
Can you send the details to [email protected]? I forgot to include the email address.
Steve

 

[j91z28d1]

you can drive the truck in the mean time in M4 mode and it won't got into auto stop mode.

do you have a scanner? how is it saying hybrid low voltage?


the switch is more difficult to explain, that's why I just said to test it jumper wire is eaiser. see if you like it kinda thing.

to wire in a switch you need what's called a single pole double throw switch. that's a on/off toggle switch with 3 terminals on it. that will allow one position to act normal and the 2nd position to tell the ecm the hood is open when it's not. for a 3 position switch, you'd have to look at the wiring diagram and figure that one out. I didn't go that deep.

take a look at the diagram in the first post to get a feel for what the ecm sees from the oem hood switch. when I get a min I'll try to send you a little crapy hand drawn diagram. it's not great thou haha.


if your pack is low voltage and it will run, you can also try this tsb first. you will need a scanner that can read at least hybrid battery state of charge. some cheap phone apps can do it. this tsb charger the battery to 70% (max charge) and then resets the computer to tell it that's 60% so that it can change the battery higher. some times over time this gets out of wack. especially if you have the battery terminal off while the % happens to be lower than 60%.

 

[j91z28d1]

here's a very crude diagram. but basically the stock switch puts ground on the purple wire when it's closed and then when you open the hood purple loses the ground and pink is the now grounded to the ecm.

the switch is wired so that in one direction it works normally, but flip it and it sends ground to the pink wire with the hood opened or closed.

the hybrid battery will still charge normally by the engine running and during regen braking. only difference is it won't go into auto stop. and you will get a dash warning that says hood open, but push any button and that goes away.