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This is probably not the place to ask my question but I haven't been on the site since it has been changed and having trouble navigating it. I typed in BCM problems and wound up here.
I bypassed my IMA a year or so ago just using the end plate and the BCM. It keeps the 12v batt. charged but it is time to smog it and I have a check engine light on and the code says my BCM connection is bad. I unplugged all of the plugs and plugged em back in but that didn't fix it. I am thinking about buying one and just trying it but having trouble finding one. Anybody have ideas to help me?
How did you bypass the IMA? Did you install an Arduino? If not, that is what you need.

 

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Discussion Starter · #102 ·
I was thinking that the PWM signal is equivalent to a voltage, in this case between 0 and 5 volts. But that doesn't seem to be true. Is this right?
PWM itself is not a DC voltage... many signal inputs that use PWM use a simple lowpass filter that converts the duty cycle to an analog voltage. However, the DCDC doesn't have said filter, and so putting an analog voltage on it won't work. You need to generate an actual PWM signal

If I can produce a 10Hz PWM at 10-90% duty and feed it to the DVCT pin (+ output to DVCT, - output to any ground, maybe the BLU/WHT SG10 GND?), will that allow me to adjust DCDC output voltage within whatever range it can do?*
Yes. If you also want 12.x mode, you'll also need to be able to pull WHT/GRN high/low.

I recommend using an Arduino Uno... it's open source and maybe five lines of code to output a PWM signal.

I saw very slow changes when I shorted DVCT to ground - it jumped up to 15.1V, but then took at least a minute or so to drop back down to ~13.8V once the short was removed...
Yes, the DCDC adjusts very quickly in one directly, but very slowly in the other. Expected behavior.
 

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Discussion Starter · #103 ·
If DVCT at the DCDC side is already 5V when the line is cut (i.e. cut DVCT, measure voltage between DCDC end and ground), doesn't that mean the output voltage is already as low as it can go?
DVCT will NEVER remain 5 volts (i.e. 100% PWM signal). Valid OEM signals are from 10% to 90% duty.
 

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DVCT will NEVER remain 5 volts (i.e. 100% PWM signal). Valid OEM signals are from 10% to 90% duty.
That's what I measure between DVCT on the DCDC side and ground, with the wire to the ECM disconnected.
 

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That's what I measure between DVCT on the DCDC side and ground, with the wire to the ECM disconnected.
That may well be the case in these circs as it probably has a pull up resistor to 5v inside for fault detection or to prevent it floating...
 

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^ That's how Mudder described it earlier, in another thread. He said there's a 100k pull-up in the DCDC. I had thought, though, that the 5V came from the ECM side...

So, if there is this 100k pull-up and I measure 5V on the DCDC side of DVCT, with ECM side detatched, while the signal from the ECM is a 0-5V 10Hz 10-90% PWM, doesn't that mean the DCDC output voltage is as low as it can be adjusted via DVCT - when it's not connected to the ECM? I.e. the PWM would have no way to pull the signal higher, 5V is the max and thus the minimum DCDC output voltage?
 

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Discussion Starter · #107 ·
Let's take a step back and look at the DCDC's wire harness (this is the DCDC's complete pinout).

These signals aren't compicated and certainly aren't terribly interesting:
BLK/YEL: +12V when key is on.
BRN/WHT: IMSSYST, this signal illuminates instrument panel battery light (light on when DCDC pulls this signal low).
BLU/WHT: SG10, essentially engine ground, referenced to a single node inside MCM.
BLK: EGND, engine ground.
YEL/BLU: TDV, DC-DC Temp. This is a static (DC) voltage output from the DCDC to tell the MCM how hot it is. The MCM uses this information to decide when to turn on the PDU fan.
(Thick) WHT & BLK wires: high current 12 volt output, bolted to the DCDC.
(Thick) ORG & BLK wires: high current HVDC input, gray connector on junction board.

These signals are interesting for our discussion:
WHT/GRN: DVC, controls DCDC output voltage mode. Open collector in ECM, pulled up inside DCDC. '14.x' mode when high, '12.x' mode when low. Purely digital signal (not PWM or analog).
GRN/BLK: DVINH, MCM uses this signal to enable/disable DCDC. 5V enables DCDC. 0V disables DCDC. This signal is always high, unless MCM thinks IMA system is super-dead, and also for a couple seconds while starting. At all other times this signal remains high.
RED/YEL: DVCT, engine coolant temp (0:5V PWM @ 10 Hz). Open collector in ECM, pulled up inside DCDC.

...

So, to power the DCDC on a bench, we have to connect:
(Thick) HVDC input, and;
(Thick) high current 12 volt output, and;
+12V (BLK/YEL), and;
ground (BLU/WHT).

That's it. In this configuration, all other signals are left floating. Since these signals are either:
-open-drain outputs (things the DCDC controls (but doesn't know or care if it's actually connected to said things)),
-or they have a 100 kOhm pullup (inside the DCDC).

In this configuration:
-DVC is pulled to 5V, thus the DCDC is in '14.x' mode (where battery temperature is able to adjust output temp).
-DVINH is pulled to 5V, thus the DCDC is enabled
-DVCT is pulled to 5V. Thus the DCDC will output whatever voltage corresponds to said signal... I'm not in front of a DCDC right now, but my memory is that the DCDC outputs ~14.4 volts. Note that this is about right in the middle of the DCDC's potential voltage output.

Note that in an OEM configuration, I have never seen DVCT exceed 90% PWM, and thus I have never seen a constant 5 volt signal... I suspect that the DCDC recognizes that the signal should be between 10:90%, and thus is defaulting to a 'safe' 14.x output voltage.
 

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I finally got something together and experimented with controlling DCDC output voltage via an external PWM signal on DVCT. I bought the PWM signal generator I linked to a few posts up - pretty cool little device. Here's an image of what I set up, with PWM duty cycles vs. DCDC output voltage at battery, posted below it. All in all it seems to work as I was trying to describe: with DVCT cut, DCDC output is as low as it can be adjusted via DVCT, and then decreasing duty increases output voltage...
82989


PWM duty cycle, DCDC output voltage at 12V battery:
100, 13.85V
90, 13.85V
80, 13.91
70, 14.02
60, 14.12
50, 14.21
40, 14.30
30, 14.38
20, 14.45
10, 14.51
0, 15.13

Oh, also, BTW, if you wanted to do this or the 'WHT/GRN' wire snip, you don't actually need to cut the wires, in case you want to cleanly restore everything later. It's really easy to just pull the spade terminals out of the connector.
 

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I was looking through the GitHub info and came across the “Always Enable DCDC” pdf. It shows the possibility for cutting two different wires, GRN/BLK and WHT/GRN. I re-read this complete thread and had a question about the wire-cuts.

The thread says, ”Also, if you've kept the MCM installed, then the MCM is disabling the DCDC converter... unless you also cut the GRN/BLK wire.

WHT/GRN= does ECM want DCDC at 14.x or 12.x volts? Cutting this wire tells DCDC "ECM wants me at 14.x volts."
GRN/BLK= does the MCM want DCDC on or off? Cutting this wire tells DCDC "MCM wants me on."

The WHT/GRN clearly increases the voltage to the 12V battery to prevent the narrow charging range. When does one cut the GRN/BLK wire? Is this related to removing the IMA battery only?
 

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^ Disconnecting WHT/GRN disables low power mode (~12.2V), keeps 12V rail at minimum of 13.85V (measured at battery). So the charging range becomes even more narrow - between about 13.85V and maybe 14.2V when cold, but generally floated at 13.85V

I think the MCM disables the DCDC only when there's a problem, such as really low IMA pack voltage and/or tap voltage. For example, when I run my pack at near rock-bottom charge state and a tap's voltage drops below 14V, the MCM commands the DCDC OFF, pretty sure that's an example of the 'GRN/BLK' wire in play... The only time I think you might want to disconnect the GRN/BLK wire is if you had a putzy pack and didn't want to do a full bypass, I guess(?). I don't know, I don't really see the point, maybe mudder will give us a valid scenario...
 

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Discussion Starter · #112 ·
The MCM also disables the DCDC when the key is 'ON' but hasn't previously been to 'START'. Cutting the GRN/BLK wire allows the DCDC to charge the 12 volt battery while grid charging the IMA battery (without having to first warm up the engine such that auto-stop works.

My general recommendation is to cut only WHT/GRN. No issues with doing that.

However, there are cases where cutting GRN/BLK can be useful, too (see above). Do note that this can cause CEL if you turn the key off and on multiple times in a row. The root cause is that if the DCDC converter's logic circuitry capacitors are still charged when the high voltage bypass contactor engages, then the DCDC will immediately attempt to draw current. Since the bypass contactor is in series with a bleed resistor (to prevent arcing across the contacts), this means the gigantic high voltage capacitors in the PDU won't charge fast enough, which will cause a CEL. No CEL will occur if you leave the key 'OFF' for ~5 seconds.
 

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However, there are cases where cutting GRN/BLK can be useful, too (see above). Do note that this can cause CEL if you turn the key off and on multiple times in a row. The root cause is that if the DCDC converter's logic circuitry capacitors are still charged when the high voltage bypass contactor engages, then the DCDC will immediately attempt to draw current. Since the bypass contactor is in series with a bleed resistor (to prevent arcing across the contacts), this means the gigantic high voltage capacitors in the PDU won't charge fast enough, which will cause a CEL. No CEL will occur if you leave the key 'OFF' for ~5 seconds.
Good thinking and an sneaky cause of illusive bypass contactor codes in some scenarios.
 

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I just wanted to give a heads up. I cut the Green / Blk Wire. I tried to remove the pin but I couldn't figure it out unfortunately, and have learned not to mess too much with the pins or you will never get them to make good contact so I just cut the wire.

I put the key to the ON position and the DC/DC converter was engaged, very nice.

I then turned the car on and off too quickly just once and not on purpose, and got a p1445 error and the car would only start with the 12 volt starter.

I reset the engine light with a obd2 reader I keep in the car and the IMA light still stayed on. I had to go and actually disconnect the 12 volt battery for 60 seconds to get rid of this error code.

It seems that just a single on/off/on too fast, under 5 seconds, will cause this issue. This kind of sucks because its so easy to restart your car too fast and then you have to go disconnect the 12 volt battery to get it back to normal.
 

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Discussion Starter · #115 ·
I just wanted to give a heads up. I cut the Green / Blk Wire...
...I then turned the car on and off too quickly just once and not on purpose, and got a p1445 error and the car would only start with the 12 volt starter.
Yes, this is a known behavior. The root cause is the DCDC remains powered for several seconds after the main high voltage relay disconnects. This means that if you turn the key back on, then the DCDC immediately starts pulling power (before the pre-charge relay can finish equalizing the voltage across the main relay); typically the DCDC has a 2 seconds blanking time between power-up and output to prevent this behavior. The MCM adds an additional delay (via GRB/BLK wire). So if you cut GRB/BLK, then you remove the blanking, introduced by the MCM.

I've been running my daily driver G1 for a couple years now with both the WHT/GRN and GRN/BLK wires cut. Note that I don't necessarily recommend this, but I personally prefer it because it lets me charge the IMA battery with the key 'ON' (but not previously started). I do not recommend cutting GRN/BLK if you are just trying to make the DCDC always charge... I only recommend cutting WHT/GRN if that's what you're after.
 

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^ I think I'm gonna try putting a switch in the GRN/BLK wire line. There's times I'd like to run 12V off IMA pack, but other times I'd rather use the 12V battery.

...Cutting the GRN/BLK wire allows the DCDC to charge the 12 volt battery while grid charging the IMA battery (without having to first warm up the engine such that auto-stop works.
Curious, how does this work? When I turn the key ON (position II), as I recall I typically see about a 5-6 amp current draw at about say 13V, which would equal about 75 watts - which would be about a 75W/156V=480mA discharge on the IMA pack...

So, if you were trying to grid charge the IMA pack with the key ON, and at the same time trying to charge the 12V battery, wouldn't the key-ON load be too much for most grid chargers to accomplish both, which are usually only 350mA output? Your 12V system would be drawing down the pack at about 480mA and you're only replenishing with ~350mA??

hmm... I think I see: grid chargers don't max-out at 350mA per se, they usually put out 350mA constant current within a voltage range. So, even though there's a 75 watt load from the 12V system, if the charger has the raw power, it will simply put out more power to uphold a constant ~350mA current. Is that right?

hmm, again: I just looked at the specs for my LED power supply charger, a Mean Well LPC 100-500. It says the rated power is only 100W. So if I were trying to charge the 12V at the same time, and 12V system power load were ~75W, that'd only leave about 25W for charging both the 12V and IMA pack. 25W/168V=149mA... My charger does a CC 500mA...
 

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mudder: Why do you not recommend disconnecting the GRN/BLK wire? Is this just for the NiMH pack or for LTO packs?
I'm running an LTO pack which I always grid charge.

I'm actually cutting the GRN/BLK because I want to be able to sit in my car and listen to the radio with the engine off. I don't need this all the time, but there are more than enough times where I have to wait in my car.

So far I'm loving it, today when I was working on my car I was able to have the radio on for hours with the engine off. My LTO pack dropped from around 2.148 to 2.133 volt per cell, not a big deal for the hours I had the car on.
 

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Discussion Starter · #118 ·
if you were trying to grid charge the IMA pack with the key ON, and at the same time trying to charge the 12V battery, wouldn't the key-ON load be too much for most grid chargers to accomplish both, which are usually only 350mA output? Your 12V system would be drawing down the pack at about 480mA and you're only replenishing with ~350mA??
There are off-the-shelf 200 W constant current chargers (e.g. PLED200W-190-C1050). However, I use a computer-controlled 16.5 amp 200 volt charger, which can of course overcome the 12 volt power draw ;).
 

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I was doing work on my car and my radio stopped functioning, but the display was still on. What happened was I ran my LTO IMA battery pack down to 2.10 volts per cell, which just happened to be 145 IMA voltage or what the car is seeing as the pack voltage.
For some reason I remember my LTO cells going below 2.00 volts under assist and resting voltage around 2.02 volts. I'm not sure what changed and why its cutting off so early.

I ran my 12 volt battery down to 8 volts because of the low voltage cutoff kicking on.

When I jumped my battery and started to grid charge my pack, the 12 volt battery was pulling 22 amps and my 2 amp grid charger was actually not able to maintain the pack voltage until the 12 volt battery got more charged.
 

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^ That seems kind of weird... You cut the Grn/Blk, right? If so, I had thought that that was one of the main reasons to cut that wire - to prevent the DCDC from being disabled by the MCM?

If it's still being disabled, then it seems like something else would have to be doing it... But what else is there?

In general, in a normal car, my understanding is that either a low tap voltage (~14V at low or no load) or possibly steep slope detection, again at tap level, can cause the DCDC to disable. I often see that behavior when I'm running the pack at near zero SoC and measuring voltage taps. But, you don't have taps, do you? And even if you did, I still don't see where the DCDC disable command can come into play with the GRN/BLK cut...

Maybe there's something else, some other circuit, that does get disabled, that affects DCDC operation? One of 'those relays' or something on the electronics board, that prevents energy from flowing to the DCDC. So the DCDC per se doesn't get disabled, exactly - but the source of its energy, somewhere between pack and DCDC, does... I'd have to look at the diagram to understand what's possible... Maybe mudder knows off the top of his head...


For some reason I remember my LTO cells going below 2.00 volts under assist and resting voltage around 2.02 volts. I'm not sure what changed and why its cutting off so early.
One explanation could be the slope detection idea. You could have cells putting out a fairly steady voltage of around say 2V under load, and a resting voltage of around 2.02V, without the cells actually being empty or near empty. The discharge voltage slope would be shallow. It's only when they are truly near empty that the slope will crater - become steep - and that's detected by the BCM. That could be how it works in a normal setup, not sure how that jibes with your LTO setup.**

If you were discharging at low current, such as with only 12V system load running the radio, then the cells could become near truly empty and at low voltage. Otherwise, normally, you can be at low voltage discharging at relatively higher currents, but never actually be so close to truly empty - so the cell voltage slopes don't tank...

** For reference, the discharge slope for my high power LTO cells starts to crater at around 2.25V at about 6A. As I recall, your high energy LTOs crater around 2V - so you'd be in the ballpark of true empty...

Looking at a discharge graph for the Fit LTOs, I see discharge slope starting to tank at about 2.1V, clearly tanking at 2V (at 0.2C rate, or about 4 amps, which is close to what you'd have with key-ON). Pretty sure that's what's causing your 'DCDC' to disable, only it's the pack itself that's getting disabled.
 
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