Does the PCM shut down the engine if the battery is not present?
03-09-2010, 06:58 AM
#1
Does the PCM shut down the engine if the battery is not present? I have been told that the engine will stop running if the battery is disconnected. Since the alternator supplies the electrical power while the engine is running, why would this occur?
Not really sure if this belongs in this section, but the PCM was the only thing I could think of that might cause this reported shut down.
Not really sure if this belongs in this section, but the PCM was the only thing I could think of that might cause this reported shut down.
03-09-2010, 07:47 AM
#2
Usually if your altenator is good the car will stay running. The altenator is supplying the voltage needed. Unhook the battery and the car dies, usually the altenator is bad. Personally I havn't tried this on the newer cars, but it worked this way on the older stuff.
03-09-2010, 10:53 AM
#3
First of all on any vehicle that has an alternator on it, disconnecting the battery is a big NO, NO. Alternators are not made to operate, with out a battery, which acts as load and a place to put their excessive output in. An unload alternator can put out in the excess of 100 volt, damaging everything from bulbs, to the vehicles electronics, including the PCM. The PCM will shut not because the battery is missing, but it will eventually do it, because the voltage got too high and its trying to protect itself
03-09-2010, 11:56 AM
#4
Thanks for the replies. Personally, I would never disconnect the battery while the vehicle is running. I understand the function of the alternator and the fact that the battery is a load when the engine is running.
However, I am being told that the battery is essential b/c the engine runs off the battery, and the only function of the alternator is to recharge the battery. I am also being told that the engine will shut down immediately if the battery is disconnected, b/c it is the sole source of power while the engine is running. This is a bit silly, IMHO, but I would like to understand why they are claiming that the engine shuts down immediately.
However, I am being told that the battery is essential b/c the engine runs off the battery, and the only function of the alternator is to recharge the battery. I am also being told that the engine will shut down immediately if the battery is disconnected, b/c it is the sole source of power while the engine is running. This is a bit silly, IMHO, but I would like to understand why they are claiming that the engine shuts down immediately.
03-09-2010, 08:17 PM
#6
So, combining your two posts, the PCM has a voltage monitor, and if it sees the voltage exceed some limit, it will shut the engine down. Would that be a correct statement? How this event is triggered (e.g. revving the engine) is not as important as the fact that it could be triggered by a sequence of actions (or inactions, as the case may be).
I'm just trying to figure out how they are obtaining their results that they are reporting.
I'm just trying to figure out how they are obtaining their results that they are reporting.
Trending Topics
03-10-2010, 09:19 AM
#8
It seems that the voltage regulator also plays a role, but doesn't fully explain why some are reporting a shut down when the battery is removed.
I am always ready to learn, which is why I participate in forums such as this.
03-10-2010, 05:59 PM
#9
I have never removed the battery completly, I just removed the positive side battery cable and left the ground in place. I wouldn't recommend removing the the ground at all. I was under the impression our altenators have a voltage regulator, which in turn keeps the voltage in check without going to high.
Not sure though, I just know that when you have a bad altenator and remove the positve battery post the car usually will die, since the altenator is not supplying the voltage needed to run the electrical system on the car or truck.
Not sure though, I just know that when you have a bad altenator and remove the positve battery post the car usually will die, since the altenator is not supplying the voltage needed to run the electrical system on the car or truck.
03-11-2010, 02:18 PM
#10
Removing the positive battery cable and not removing the ground, isn't helping anything. Electricity needs a complete circuit...the ground terminal of the battery is useless without the positive terminal being connected too because the battery is no longer part of a circuit.
Much in the same regard, the alternator can only put out current because it's case is the other end of the circuit...if you trace the ground cable off the battery, you will see that eventually it connects to the engine (either directly or via the engine and the cable both being connected to the chassis). The alternator case is also connected to the engine (vie a bracket)...if the alternator were attached via plastic, rather than metal (including the bolts holding it on) it wouldn't charge the car.
Much in the same regard, the alternator can only put out current because it's case is the other end of the circuit...if you trace the ground cable off the battery, you will see that eventually it connects to the engine (either directly or via the engine and the cable both being connected to the chassis). The alternator case is also connected to the engine (vie a bracket)...if the alternator were attached via plastic, rather than metal (including the bolts holding it on) it wouldn't charge the car.
