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So around the middle of January, my radiator cracked wide open on the highway while out of town. As luck would have it, I was within towing distance of a mechanic shop where my friend works. Normally I do my own repairs, but this guy and I get along well, we've worked together on projects and he's very meticulous. Bottom line is I trust him and still do.
Skip forward to today.... one of the first sunny and warm Saturdays in the midwest. Giving the ol' girl a bath and decide to pop the hood and blast the bugs out of the radiator. Then I noticed something...
When I disconnected the infamous electronic motor mounts several years ago, I wrapped them in plastic secured with a zip tie around each one, I guess as a signal to me "It's ok, you did this" in case I somehow forgot what the deal was.
Well, it seems the friend saw this and thought "these are supposed to be connected" and re-hooked them for me. And I've been driving an insane amount of miles with these connected, and I'm at 127k now... like right in the ballpark for "somethings gonna kill the ECM any second now" time.
(taking zen position... finding peace... breathing...)
So anyway. As I googled a bit to make sure I was unplugging the correct wires, I found this. Thought it would be good for a lot of us to read. I'm going to do the fuse swap right now. I've not heard of that before.
lol, maxiiiboy wrote this and posts this in about every motor mount and p0505/iacv thread that surfaces. its on here all the time i'm surprised you haven't come across it yet. good info in there and i agree should be a must read for any new 5gen owner.
there's nothing like buying a $1500 car and having the dealer tell you to spend $1500 on a new ecu
Unfortunately, the 7.5A fuse swap does not guarantee that the ECU will be protected. The 7.5A fuse swap will reduce the probability of failure, but it does not guarantee ECU protection; in fact, at least one member reported ECU failure even with the 7.5A fuse.
For guaranteed protection, you would have to protect each STA509A transistor within the ECU with either a 3 Amp or 4 Amp fuse and that's impossible without cutting/splicing the harness.
I know how to do this properly but for the time being, I have decided not to do any harness cutting/slicing. I also have an updated version of the document but have not posted it in all the right places yet.
Sorry for the delay in responding; I have been off the air for a while.
For guaranteed protection, you would have to protect each STA509A transistor within the ECU with either a 3 Amp or 4 Amp fuse and that's impossible without cutting/splicing the harness.
I know how to do this properly but for the time being, I have decided not to do any harness cutting/slicing. I also have an updated version of the document but have not posted it in all the right places yet.
^Will this prevent a 5.5 gen front mount from shorting the ecu if it goes bad? Sashaoven spliced in a 2 amp fuse. I'd like to plug mine back in if I can just to smooth out the idle a little.
I've been working in electronics almost 50 years. There's an old adage that goes something like this: Never trust a fuse to protect a transistor. The reason for this is that most fuses take much longer to blow open than it takes for a transistor to destroy itself when there's an overload. I would trust an electronic (transistorized) current limiter in line with each motor mount, but not a fuse. If you're not prepared to DIY something like that, my suggestion is to just unplug the mounts and live with the rougher idle.
I would trust an electronic (transistorized) current limiter in line with each motor mount, but not a fuse. If you're not prepared to DIY something like that, my suggestion is to just unplug the mounts and live with the rougher idle.
Current flow in this circuit is from the battery to the coil in the motor mount. The other end of the coil is wired to a transistor in the ECU. When that transistor is turned on, it connects the voltage to ground, completing the current path. Normally, the current is limited by the DC resistance of the coil in the mount. However, when the coil shorts internally, its resistance goes down. That allows excessive current to flow through the transistor when it turns on, destroying it.
One solution to this problem is to install an electronic current regulator between the mount and the ECU. The regulator will limit the amount of current that can flow into the ECU. Even if the coil in the motor mount shorts, the limiter will prevent excessive current from flowing. It will do this automatically, no fuses will blow, and the only symptom will be an inoperable mount.
I don't know how much current is drawn by each motor mount, but if it's less than 1.5 amp, the info below provides a solution. It's based on the LM117 IC (commonly sold in the LM317 version). This three-terminal part is very cheap, and it can be wired as a current limiter using only two external parts.
The first image below shows the IC and a schematic using it as a 1 amp regulator. In the schematic, Vin would connect to the wire coming from the motor mount. The LOAD would be the wire going to the ECU. The way this works is that the LM317 will attempt to pass 1A to the ECU at all times. It does this by controlling the voltage between its input and output. In the case where the motor mount has shorted, the LM317 will drop nearly the entire 12V across itself in an effort to limit the current to 1A. This removes most of the voltage from the transistor in the ECU, allowing it to turn on without being damaged.
The second image below is another version of the schematic that includes formulas for determining the value of the current set resistor. The LM317 will regulate at 1.5A using a 0.833 ohm resistor (a 2 ohm and a 1.5 ohm in parallel will be very close).
Note that if the coil shorts, the LM317 will dissipate 12W (1A setting) to 18W (1.5 amp setting). Although it is said to incorporate thermal shutdown protection, a heatsink is needed for operation at these levels.
Electronic motor mounts eh? Neat.
Wow thank goodness all I have to worry about are the pre-cats failing and eating my engine.
Just to verify,electronic Motor mounts only on autos?
Last edited by wellshii19; 05-04-2017 at 01:13 PM.
Your pre-cat would have to be pretty bad to damage your motor! That's why you resolve the P0430/420 so they don't catch fire and plug up.
I wouldn't know about engine mount failure damaging an ECU because someone already had the ones in my car unplugged before I bought it!
Thanks for the reply jackman! LM317 can be found online assembled with a heatsink. How can we find the current drawn in amps? Is it as easy as checking the amps in DC with a multimeter between terminals 1 and 2 on the front mount going to ecm? Does it matter if it's measured under load or at idle? The mount is supplied 0-1v at idle and battery voltage under load.
In the schematic you posted, voltage from the battery is connected to each motor mount at terminal 3. Current flows into/through the mounts from terminal 3 to either terminal 1 or terminal 2, depending on whether the ECU is locking or unlocking the mounts. To measure the current, you'll need to cut the wire going to terminal 3 and insert the ammeter there. That's also a good place to install the limiter. Another way to do this is to unplug a known-good mount and measure the resistance between pins 3 and 1, and between pins 3 and 2, with an ohmmeter. Current can then be calculated using Ohm's law: Current = Volts ÷ Ohms. I haven't been under my 2000 yet to look at this, so I don't know how accessible those pins are at the mounts.
The LM317 modules sold online are probably wired as voltage regulators, not current regulators. You'll need to modify the PC board a little and add a current set resistor to use those. The potentiometer can't be used as a current set resistor, but there should be pads on the board that will work to solder the new resistor in place.
I just want to add that once the current is known, you also have the option of installing a fast-blow fuse rather than the limiter. The electronic limiter is safer for the ECU, but I realize the process might be too complicated for most owners.
The LM317 modules sold online are probably wired as voltage regulators, not current regulators. You'll need to modify the PC board a little and add a current set resistor to use those. The potentiometer can't be used as a current set resistor, but there should be pads on the board that will work to solder the new resistor in place.
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I only have an electronic front mount. The connector F23 is easily accessible. It is next to the line up of connectors on the front of the motor. It is a brownish in color and mounted to one of the coolant pipes on the front of the engine. I think the connector for the back one would be right under the airbox if I had one. I'll check the resistance you mentioned when I get a chance.
Thanks for the reply jackman! LM317 can be found online assembled with a heatsink. How can we find the current drawn in amps? Is it as easy as checking the amps in DC with a multimeter between terminals 1 and 2 on the front mount going to ecm? Does it matter if it's measured under load or at idle?
Don't bother to chase down the draw.
There is an easy answer: The STA509 transistor in the ECU (which drives the motor mount) is rated at 3A in steady state and 6A in pulse mode. So, your protection device needs to be rated correpondingly.
Don't bother to chase down the draw.
There is an easy answer: The STA509 transistor in the ECU (which drives the motor mount) is rated at 3A in steady state and 6A in pulse mode. So, your protection device needs to be rated correpondingly.
Two comments on this...
First, if it's desired to use a fuse, it should be sized close to the actual current draw, with maybe about 1/2A additional. IOW, if the current is 1A, you'll want a 1-1/2A fast blow fuse. This means that simply knowing the rating of the transistor isn't good enough.
Second, the LM317 is only rated for 1.5A. So, if it turns out that the current draw is 2A or 2.5A, (which is still within the ratings for the ECU transistor), the LM317 won't work.
Maybe I should have recommended the LM338 instead. In the TO-220 case style (same as the one shown in the images I posted), it's less than $2 in single quantities from companies like Mouser Electronics. It's rated for 5A continuous, 7A peak. The current set resistor is calculated in the same way, so it's a direct substitute for the LM317. Just remember that the higher it's set for current limiting, the larger the heatsink will need to be. 3A x 12V is 36 watts, and that would require a pretty big heatsink. Of course, it will only dissipate that much if the motor mount shorts. Under normal conditions, it will dissipate very little.
Just to be clear, I'm only throwing this out for general consideration. It's a fair amount of trouble to do something like this, and I won't even do it myself if I can live with the mounts disconnected. If I have time this weekend, I'll try to determine the actual current flow. If it's small enough, a fuse might prove to be almost as good a solution. It just depends on how close the actual draw is to the rating of the transistor. If the motor mount draws 1A, a 1.5A fuse would probably protect the transistor. OTOH, if it draws 2.5A, the corresponding 3A fuse would be a poor solution.
First, if it's desired to use a fuse, it should be sized close to the actual current draw, with maybe about 1/2A additional. IOW, if the current is 1A, you'll want a 1-1/2A fast blow fuse. This means that simply knowing the rating of the transistor isn't good enough.
Second, the LM317 is only rated for 1.5A. So, if it turns out that the current draw is 2A or 2.5A, (which is still within the ratings for the ECU transistor), the LM317 won't work.
Maybe I should have recommended the LM338 instead. In the TO-220 case style (same as the one shown in the images I posted), it's less than $2 in single quantities from companies like Mouser Electronics. It's rated for 5A continuous, 7A peak. The current set resistor is calculated in the same way, so it's a direct substitute for the LM317. Just remember that the higher it's set for current limiting, the larger the heatsink will need to be. 3A x 12V is 36 watts, and that takes a pretty big heatsink. Of course, it will only dissipate that much if the motor mount shorts. Under normal conditions, it will dissipate very little.
Just to be clear, I'm only throwing this out for general consideration. It's a fair amount of trouble to do something like this, and I won't even do it myself if I can live with the mounts disconnected. If I have time this weekend, I'll try to determine the actual current flow. If it's small enough, a fuse might prove to be almost as good a solution. It just depends on how close the actual draw is to the rating of the transistor. If the motor mount draws 2.5A, the corresponding 3A fuse would be a poor solution.
Slow down - you are overthinking this!!!
If you manage to limit the current to 3A, then the ECU transistor will never get damaged - never.
This leaves the pulse mode operation for which up to 6A may be required. Why don't you reason about a possible protection as homework ..... .
If you manage to limit the current to 3A, then the ECU transistor will never get damaged - never.
But like I said, the LM317 that I recommended at first can't handle that much current. That's why I suggested measuring the current, and also why I offered a higher-current alternative. If this is too much information, just ignore it. Maybe someone else will find it useful.
Jackman, I appreciate any effort/thought you're putting into this because it isn't really necessary. I just thought it would be nice if I could come up with a simple solution to plug my mount back in.
Second, the LM317 is only rated for 1.5A. So, if it turns out that the current draw is 2A or 2.5A, (which is still within the ratings for the ECU transistor), the LM317 won't work.
This confused me. When I looked into the LM317 I noticed it was rated for 1.5 volts. Did you mean volts or is it also only rated for 1.5A when used to regulating current?
If you manage to limit the current to 3A, then the ECU transistor will never get damaged - never.
This leaves the pulse mode operation for which up to 6A may be required.
As I understand it a fast blow fuse only works when there isn't a surge upon powering up? So assuming there is no surge and a fast blow fuse would work why not just throw in 6.25A fast blow fuse and call it a day. Would 6.25A damage the transitor?
The LM317 is rated for 1.5A maximum current, regardless of whether it's wired as a voltage regulator or a current regulator. A 6.25A fuse will probably not protect the transistor if the motor mount shorts. You could try 3A, but even then, it's impossible to know for sure. The transistor's "survivability" is dependent on the resistance of the mount when it shorts and the length of time it takes the fuse to blow. If you really want to use a fuse, it's necessary to know the normal current draw in order to achieve the best protection for the transistor.
Ok, when I said 6.25A(or 6.5A .5 amp more) I thought the fuse would have to be higher than the 6A rated pulse mode. So that there was enough current for the pulse mode to operate.
The pulse rating of the STA509a is only intended to indicate the peak current capability of the device under short term conditions. The 6A specification is for a pulse width not to exceed 100 micro-seconds, or 0.0001 second. The motor mounts aren't being pulsed, so this data is only relevant insofar as it tells us something about the life expectancy of the transistor when the coil shorts.
Just to put fuse protection into perspective, the chart below shows the blow time for Bussman AGC fast-blow glass fuses. If 6A is applied through a 3A fuse, the fuse will open in approximately 0.6 seconds. That's 6,000 times longer than the transistor is rated to survive.
Ok, so pulse mode will operate(probably wrong word) with a 3A fast blow fuse and probably a smaller fuse because the transistor is likely only switched on for micro seconds. However, it would have to be at least 3A (or over actual current draw) because that's the steady state which it's in for extended periods? It sounds like a fuse would never work because the fuse would never blow in time before the transistor became damaged.
It sounds like a fuse would never work because the fuse would never blow in time before the transistor became damaged.
Maybe this is the reason some owners have reported failures even after installing a fuse. A 1A fuse still requires 0.035 seconds to blow at 6A. That's 35,000 micro-seconds. In comparison, the LM317 exhibits a transient response time of 50 micro-seconds. The LM338 is less than 35 micro-seconds.
In comparison, the LM317 exhibits a transient response time of 50 micro-seconds. The LM338 is less than 35 micro-seconds.
Wow. So, I guess there may be no simple solution besides unplugging the mount.
With the limiter you couldn't limit it at 3A or pulse mode wouldn't switch on. You also couldn't limit it at 6A or the transitor would be damaged. Is that what maxiiiboy was getting at?
There's no "pulse mode." The ECU in our cars doesn't do that. Applying a short, high-current pulse to a transistor is simply one of the ways manufacturers rate their products. It helps design engineers understand the dynamic capabilities of the part.
I was too busy this weekend to crawl under the car, but I did find the engine compartment connectors for the mounts. I took this one apart, then used an ohmmeter to check out the three pins going to the mount. Nada. Nothing. No conduction from any pin to any other pin. Guess I'll need to get under there next weekend to see if someone disconnected it at the motor mount.
That's strange. That is the mount's only connector, connector F23. There is no connector at the mount. F18 is probably shared so it wouldn't be disconnected there, and it wouldn't be disconnected at the ecu. Maybe someone pulled the fuse.
Yep, I'm stumped, too. When connector F23 is separated, the vehicle's harness is totally disconnected from the front mount. The half of the connector that's left hanging on the bracket has a three-conductor cable that only goes down to the mount. It doesn't go anywhere else. According to the schematic, the bottom of the cable is actually a permanent part of the mount. If there's no continuity at the connector, one of two things has happened. Either both coils in the mount are open - which seems unlikely - or the cable is disconnected/damaged/cut closer to the mount. I'll need to get under the car to find out what's going on. I wanted to look at F9 too (rear mount), but part of the air intake has to be removed for access. It's a simple job, but I didn't have time today.
Incidentally, there's an error in the pictorial drawing of the rear mount connector. The object where the drawing indicates the battery should be is actually part of the air intake system. The battery is in the opposite direction, shown by the red arrow.
04-16-2016, 10:41 AM
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