Well, lets think about this a bit. In the headlight analogy, you are talking about an OPEN circuit. In this particular instance here, we are discussing a SHORTED circuit. Two completely different situations, and not even remotely comparable.

Electricity takes the easiest path. No matter if it is parallel, or series. If you short one branch to ground, that is the path the current is going to take. Shorting one branch of the 5v supply to ground is going to take out ALL OF THEM. If the cranks position sensor isn't getting its 5v supply, it sure as hell isn't going to give a signal to the PCM, so, the pcm triggers the ASD event. End of story.

 

Stands,

What your implying / saying is that all the remaining sensors are going to still receive proper power despite shorting the supply. That is like saying that, if you short out one wall lamp out of five on a particular CKT, that, the four remaining lights on that same CKT will illuminate. Take a lamp cord, short the hot to ground and watch what happens. The remaining lamps on that CKT are NOT going to be getting ANY power because, if and when the supply is shorted, either a fuse or breaker is going to blow or trip thus, cutting power to the entire CKT. This is a failsafe event.

But, do test that out. Short out one lamp's HOT to ground and note if the remaining lights on that CKT illuminate.

That is incorrect. For those who own the Haynes manual, please note the ASD relay function found in Sec 6-5 for more information. In the 2001 manual, please turn to page 541, Sec 81 - 4 Automatic Shutdown Relay

The following excerpt noted in blue was derived from the 2001 manual.


When the PCM de-energizes the ASD and fuel
pump relays, terminal number 87A connects to terminal
30. This is the Off position. In the off position,
voltage is not supplied to the rest of the circuit.

The PCM relay control (PIN 51), is a switched ground for the coil side of BOTH the ASD and FUEL PUMP relay PIN 85. In automatic shutdown mode, the PCM opens this return path, thus no power to the fuel pump relay coil thus, it's not energized, thus, no contact is made thus, no voltage is sent to the fuel pump.

Further evidence also found in that same manual can be found for the fuel pump relay during KEY <ON> event on page 1528 titled, Fuel Pump Relay. This is also an automatic shutdown event as, if and when the engine is not running, the PCM initiates the automatic shutdown command thus cutting power to BOTH ASD and FUEL PUMP relays as they are tied into the same switched ground at the PCM.

EDIT: The following excerpt noted in blue was derived from the 2001 manual.

The Powertrain Control Module (PCM) energizes
the electric fuel pump through the fuel pump relay.
The fuel pump relay is energized by first applying
battery voltage to it when the ignition key is turned
ON, and then applying a ground signal to the relay
from the PCM.
Whenever the ignition key is turned ON, the electric
fuel pump will operate. But, the PCM will shutdown
the ground circuit to the fuel pump relay in
approximately 1–3 seconds unless the engine is operating
or the starter motor is engaged.
CM

 

You got that. End of story.

CM

 

Apples to apples plz.your both comparing a high voltage , high amp AC circuit that uses breakers to a low voltage/amp DC automotive circuit that uses simple fuses.plz can we stay on the topic of a automotive circuit.

Back on topic.why doesn’t the fuse blow for that circuit when a 5v sensor shorts?it’s the design of the parallel circuit combined with low voltage/amps.OHM’S LAW repeats its self….again…. furthermore each branch in this circuit has it OWEN PATH to the voltage source and if a single branch go to short the remaining branchs remain energized.now if the voltage source before the branch is shorted then all circuits de-energize and in this case it would be a short within the splice and/or joint connector within the PDC.can you agree that it’s a parallel circuit? Did you know a sensor/device can short internally to ground ?did you know theres DTC’S for a short in a circuit? .

ASD RELAY AND EVENT with a good circuit…...the ASD RELAY only supplies voltage to the crank sensor,coil and sometimes an o2.ASD RELAY is apart of the ignition system not fuel system.AS PER THE FACTORY SERVICE MANUAL (FSM).if you want to disagree with mother mopar then that’s your prerogative.

1.if the pcm de-energize’s the fuel pump why would it de-energize the injectors to?
2.if the pcm de-energize’s the injectors why would it de-energize the fuel pump to?
3.what would be the reasoning for the pcm to de-energize both in this event?

ASD RELAY and fuel pump relay both share the power from the joint connector within the PDC.that’s the only CIRCUIT THEY SHARE which is pre relay..if that joint connector within the PDC shorts you’ve got bigger issues and the PDC would need to be replaced as a whole unit.ASD RELAY is on circuits A16,K51,A142.FUEL PUMP RELAY is on circuits A14,K31,Z1(ground),F18,K131,A40,A61.as you can see we have completely seperate circuits controlled independently by the PCM...but feel free to disconnect the crank sensor or remove the ASD RELAY (wont harm any circuit)and turn the key on.you will hear the fuel pump energize/come on for approx 3 seconds.an enegineer would know this info.in conclusion I believe iam beating a dead horse.peace out.

 

Power source for Cranks Sensor: C1 pin 17.
Power source for Cam Sensor: C1 pin 17.

Same source. Ground one, ground them all. With a single source, current WILL take the path of least resistance. Ohm's law is irrelevant here. The PCM is fused, and the five volts to ground is not going to be a big enough draw to blow any fuses. The specific circuit in question does not have a dedicated fuse.

The PCM energizes the fuel pump relay for a few seconds at key on. If the starter isn't engaged, or the engine isn't perceived as running, it will turn it off. If the power supply to the crank/cam sensors is grounded, the PCM will only run the fuel pump if it sees the starter motor running. It sure isn't going to get a signal telling it the engine is turning....

In any event, I really don't quite get why you are so adamant on this. Nor have I seen any qualifications from you on just why we should take your word on it, as opposed to someone else's real world experience. Are we to buy into your conspiracy theory here that Mr. Mckenna puts these people up to these threads? I am quite sure he has far better things to do. Including arguing with you. In fact, I am going to bow out of this now, as I suspect that you are going to stick to your guns, and continue arguing the point regardless of what evidence there is to contradict you. I am done. Welcome to my ignore list. Congratulations, you are the first to make that distinction.

 

Stands,

The reason why the five volt CKT does not blow a fuse is because, this supply is derived at the PCM internally. 12 VDC in, and, it's got two supplies both of which have INTERNAL failsafe mechanisms which, will do just that to prevent killing the supplies under a dead short condition.

Any power supply, AC or DC can be shorted and, depending on design, it may be externally fused or internally failsafe protected to which, the PCM uses use some failsafe mechanism such as a solid state relay or breaker. I use the AC lamp analogy as it is a simple and common household thing to grasp, as a general concept of dead shorting the supply.

Something else about the shared CKT involving the ASD relay and FUEL PUMP relays that is important is, it's not just about the HOT but ground as well. The HOT does nothing without a path to ground. This makes a complete CKT. So, ground is equally just as important (if not more so if and when they go bad) than the plus side.

This ground switch is located INSIDE the PCM Stands. It is switched internally via most likely by a 5-volt solid state relay inside the PCM. This signal, runs through the PCM and is connected to ground. Here, both relays are tied together from the load side of the coil - not the B+ voltage side. So, you must move past the PDC and follow it / trace it all the way back through the harness into the PCM.

When the PCM switches this OUT of CKT, there's no GROUND path for the electricity to flow to ground. If there's no flow, you've got zip on that CKT. And, since both of those relays are on that same CKT, the status for both is OFF. No flow.

Do you have the Haynes manual at least? The wiring diagrams would be a good place for you to start looking for, in the engine control wiring diagram, it provides a lot of information just based on that one simple drawing. You can also look at the wiring diagrams online as well as the manual for later Dodge Rams that are available for download online.

I know what you're thinking but, it doesn't supply the CKPS with voltage for, the PCM supplies the five volt supply directly to that. The voltage present at the ASD relay is from B+ and is 12V not from the 5-volt supply that feeds the CKPS.


I highly recommend to look at those drawings, flow diagrams as well as the wiring diagrams because, it's all right there.

If I didn't have to start packing up tomorrow morning and put in fog lights and a tach and new injectors in my own truck this week in prep for my move, I would take the time to scan them as well as highlight those CKTs for you and post it on here so you could see it. Once you see it, you'll understand how this system works. In order to see this, this is where I believe drawings present the big picture. It's fully laid out in front of you clearly giving full access from start to finish without obstructions as one would find on the vehicle because, in order to fully understand one CKT at the vehicle level, the CKT must be manually traced out through wiring harnesses, connectors, the firewall, and, since a lot of them all tie into the same splices and grounds and other components, it can be difficult to isolate the CKT that you're looking for without the schematics and / or wiring diagrams.

For the answers to these questions:

A: Since the fuel pump relay is not isolated from the ASD relay CKT (shares the same ground path) when the PCM switches the ground OUT of CKT, power is cut to BOTH thus, the reason why no power is witnessed at the pump, the coil, the injectors etc.

Same reason as above Stands.

3. A: There is not an option to shut one or the other off independently. When that ground is switched out, both are affected. Does this make sense? I hope so. I see you wanting to learn here which is good and, the answers to your questions are going to help you to understand this system a little bit more.

Stands, you are not beating a dead horse you're just stubborn. You just didn't communicate or ask the right questions until tonight. Now that you're asking questions, I know why your confused. This is good because, I can clear this up.

What you're talking about above is totally a different situation. What you describe is simply removing the ASD out of CKT. Well, let's look at the condition that the PCM is in or, better term for this would be: mode. What mode is the PCM in? It's in normal operating mode. It's not in failsafe mode / auto-shutdown mode. That being said, the PCM has not executed the failsafe command.

Therefore, since no failsafe event has been triggered, that switched GROUND that I was telling you about - at the PCM; is functional thus, during a KEY <ON> event, it energizes the FUEL PUMP COIL inside the relay thus making connection to the fuel pump. There's your answer to that question Stands.

Same applies to the CKPS at time of KEY <ON> event. Even if the sensor is out of CKT or, not functioning ok, it will not induce the failsafe mechanism at the PCM program level. It will trip an OBD code but, it's not going to trip the mechanism in this case and, the PCM will be in full operational mode.

On the other hand, if you dead short the supply, it will send the PCM into auto power down mode thus preventing it from burning up the supply inside of the PCM. This is why it also can't be communicated with off the OBD connector under the dash. It's not even running idle mode. Key sense is not even operational so, "wake up state" does not function either.

Engineering in this manner is very smart. They know what the risk is of shorting a supply in the engine bay due to a melted wire or whatever, and, in order to protect the PCM, engineering designed in a failsafe mechanism. This mechanism just so happens to be internal to the PCM vs externally fused. This is also why no fuse pops. This is implemented on a vast scale in the industry. Power amps, car stereos, converters, clocking devices, vacuum tube amplifiers and DACs etc use failsafe circuits to prevent a catastrophic event from killing the power supply. Some use internal fuses, some use solid state relays that run on 5-vdc which, is fairly common as they are very reliable, very cheap, and unlike fuses, you don't have to service the unit to replace the fuse.

Take care,

CM

 

I just want to make sure all info is accurate here. In a parallel circuit, you have electricity available to all branches regardless of what happens to an individual branch. But its important to know what part of the electricity is available. And what I mean is that voltage is split evenly, regardless as to what is happening at the other branches. So you have a 5V source, all branches of the parallel circuit will receive 5V, regardless. However, that is not true of current. Current is divided up. But when one of the branches is shorted and draws infinitely, it totally throws off all preconceived current draws. it changes the current draws and even the total voltage output because of this. If you are not familiar with this, look it up. So the 5V reference source is even going to be effected as internal resistance at that source is going to change because of the shorted branch circuit.