Hi everyone,

I'm new here. I wandered into this esteemed forum after searching high and low for answers. I'm stumped. Maybe y'all can help me... I hope...

We own an '09 Ram hemi 2500. Big brute -- very nice indeed!

A bit of background first: Being the unusual, geeky, gearhead sort of gal I am, I've been designing and building electronic devices now for decades. I've dealt with enough electronic devices to know that even the best of them can fail. My last car, made by a non-Dodge manufacturer I cannot name, deployed a system I cannot identify, possibly injuring me (or not). I can't say much more than that, because I signed a legal document that I would not. Anyway, this reinforced my distrust of complex electronic devices -- even the ones that are supposed to be the most rock-solid, safety-related ones.

When I first heard of electronic throttle control (not meaning a bypass mechanism for idle control, but the main throttle), I thought "Gee, this is a horrible idea just waiting to kill someone. Sure enough, Toyota is proving this to us right now. Prior to all the news breaking about the Toyotas (and Chinese-market Fords), we bought our Dodge, which of course has a dreaded electronic throttle control. (Yes, I know there are no issues with the Dodge throttle control systems, but I'm not comforted that they are of a cheaper design than the Toyota units (which are Hall effect sensors, as I understand, rather than Dodge's potentiometer pedals). Anyway, the bottom line is that I just don't trust the things. Eventually the throttle body and/or pedal WILL fail, and the failure mode could be just about anything. Murphy's law would dictate we'll find out what that failure mode is when we're flying down a long grade with a few tons of trailer behind us!

Understanding this, I want an engine kill switch. Common sense dictates that every potentially dangerous piece of equipment should have an emergency shutoff. In the case of a vehicle, this switch would double as a theft deterrent.

The approaches I've explored:

My first thought was to interrupt the fuel pump relay, which would seem simple enough. Nowadays these things seem to be located alongside fuses in the power distribution center. No such luck with our '09 truck. From what I can find on the Internet, they did that back in '05, but apparently not now.

Anyway, we went to the dealer today and pitched the question to them, asking them where the relay is. The service rep told me it's in the PDC and was initially surprised to find it wasn't there. Then he said, "Oh, yeah, this is one of the new models with the __???___, which shuts down the fuel pump in the event of a rollover." He went on to explain the whole thing is integral and possibly stuffed into the fuel tank. Hmmmmm....

OK, then I probed him for alternative ideas. We went through the fuses together and found #22 (? -- gray 2A), which is the ignition key feed. We both agreed that was a good approach! I thanked him and sheepishly told him yet again, "I just don't trust these things." He waved, walked away, and muttered under his breath, "I don't blame you."

So I got home and pulled the #22. I turned the key, and no start. OK so far. Then I replaced the fuse, started the engine, and pulled the fuse to confirm that it killed the engine. Nope! Still running. The reason? It's probably because the ignition key simply sends a logic signal to the ECU, which starts and stops the engine.

Then I looked through the list of fused circuits for some other critical engine circuit -- probably the ECU or fuel pump. Unfortunately the only engine component I could find there was the oxygen sensor. That wouldn't help.

Then I looked throughout the engine compartment and under the dash for ANYTHING that would look like a fuse, a fusable link, or a relay. Nothing.

I'm stumped!

What can I do to kill the engine with a switch? I'm looking for a solution that won't get too invasive. My original plan with the #22 was to plug in an "add-a-fuse," which I would modify with a relay in series. That mod could be reverted back to stock merely by unplugging it and plugging a fuse back in. A relay mod would be done by modifying a relay with connector on the ground side of the coil that would run to a switch. Again, that could be reverted back to stock by unplugging the modded relay and replacing it with a stock relay.

Any ideas?

Thanks everyone!

Peace,
Sarah

 

Disable the power to the PCM

 

ChryslerTechBC, that would probably work fine, but I can't find any point where I can do that without cutting wiring (and possibly voiding warranties). Besides that, the service manuals aren't out yet, at least for private owners like me, so I wouldn't even know what wire to cut. As I recall, there are four huge wire connectors streaming into the thing. Is there a fuse for the thing somewhere? Maybe a fusible link?

To be honest, this truck is a bit of a space ship, compared to what I'm used to working on. ;-)

I'm still wondering about the fuel pump wiring. Can anyone tell me more about how it's wired? Is there a schematic anywhere?

Thanks again, everyone!

Peace,
Sarah

 

You know I have thought about this question before and I came to two conclusions.

1. Just turn the ignition off, I know the power sterring will go away but better then running into something.
2. Put the truck in neutral and let her blow. Hopefully you will get off to the side of the road first and then you can turn off the ignition switch before the engine blows.

Either one of these seems pretty easy to do in case of emergency and you do not have to spend any money on them either.

 

http://www.caranddriver.com/features...tion-tech_dept

 

I came to some of these same conclusions, but I really sat up and took note with the Congressional testimony of one woman whose Lexus had this problem. She had trouble braking, even though she was standing on the brake pedal with both feet. I thought about that and realized that the maximum braking power is governed by the vacuum to the power booster. At WOT and under load (accelerating), the vacuum can be rather low, so the balance of power can shift to the engine over the brakes.

Then she described how she shifted into reverse to try to stop the car. Nothing changed, and the car was still out of control. No doubt the transmission was electronically controlled, and shifting into reverse while flying down the highway at 100mph was probably deemed by the computer as unwise. Therefore the driver was overridden. Neutral might also be considered unwise, but it's hard to say without testing it or talking to the engineers.

And then there's turning off the ignition, but again, the modern ignition switch is a logical device that tells the ECU or PCM to go ahead and start or stop the engine. This would be subject to override too.

Finally, all of this presumes the PCM is capable of making good decisions. If the firmware becomes corrupt, or if the operating program becomes "confused" because a few bits have been flipped by a voltage transient, there's no telling what the device might do.

These aren't the same machines we drove 20 years ago. The PCMs are a lot smarter now, they do much more microcontrolling of the vehicle's operation, and they are designed to override the driver's actions if the driver is found to be in error. All things considered, I think I still need that kill switch!

 

Seems more likely that cobbling into the wiring is more likely to result in a bad situation than being the unlucky person that has a computer glitch.

The lady in the Lexus story brings up a lot of questions because it just doesn't sound right. Neutral would have been a wiser decision for the lady in the Lexus, and even with no boost to the brakes both feet on the pedal would stop any vehicle I've ever driven including a twin axle 40K lb farm truck.

 

For what it's worth, looking at the hydraulic diagrams for a U140E transmission (Lexus RX300 tranny) Reverse and neutral are a mechanical valve, the electronic solonoids only control the forward gears and only when it is mechanically in the drive position. SO the computer didn't do anything to stop reverse, but if she truely was going 100mph when she shifted to reverse - she probabally blew something up in the tranny instantly.

I also notice that you have a 2009 2500 - that would be a Gen 3, not a Gen 4. Might have better luck finding the electronic info you are looking for in the Gen 3 forum.