Opened the traction battery and found the Pre-charge resistor was bad. What caused it to fail?

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braebyrn

Well-known member
Leaf Supporting Member
Joined
Nov 14, 2013
Messages
97
Location
Seattle, WA
Thanks Mux for your help in figuring out that the pre-charge resistor in the battery junction box was bad. Also a big thank you to the others that have contributed videos and forum discussions pertaining to opening the case and troubleshooting the issue discussed here http://www.mynissanleaf.com/viewtopic.php?t=21776

What caused it to fail? I followed the steps on the service manual by checking ohms on the heater, compressor, inverter, and opened the DC to DC junction box and checked the fuses and came up blank.

Now that the precharge resistor is replaced, I don't want to have to drop the battery again because I missed a bad/failing part that caused it to fail to begin with.

Original error codes C118C, C1A6E, C1A70, P3176, P311C,

C118C 0109 ABS EV/HEV System BRC-126
C1A6E 0109 BRAKE EV/HEV System BR-146
C1A70 0109 BRAKE Brake Control System BR-160

Below codes are the real issue...
P3176 00C0 EV/HEV Inverter Condenser EVC-238
P311C EV/HEV High Voltage Sys EVC-204
 
All the codes have cleared and the car now takes a charge. I haven't turned on the heater or cooling compressor. When I did turn on the car for the first time (not with brake depressed) the defrost button started flashing. IS THAT NORMAL?

The original owner said that she turned on the defroster, left the car for 20 minutes and when she came back the car was dead. After charging the 12 volt battery, the car would not go into drive or reverse and the heater and defroster would not work either. Nor could she charge the car.

Could that be the culprit causing the pre-charge resistor to blow?

I am afraid to put the car to the run (with the brake pedal depressed while pushing the ignition button) state for fear of blowing the new one....
 
Well the new precharge resistor should have been used while "booting" the HV bus when initiating charging. I would start it up. It is a car after all, if something's still broken, no sense in having it sit at this point as a paperweight.
 
With a 2012 SL as my daily driver, it can sit until It can be determined what is causing the failure. It's not that hard to drop the battery, undo the cover and dig into the battery block, but it is time consuming.

Was hoping someone has some better idea where to look next for the answer.
 
I understand the purpose of a pre-charge resistor, but don't know how it's implemented in LEAF. I would want to know whether the resistor is always in the circuit or if there is a relay or contactor intended to remove it from the circuit before the main contactor closes. If so, then perhaps the precharge relay is stuck closed.
 
Hello,

At work we have some precharge resistors on capacitors or large motor line.
Sometimes they burn, the reason can be multiple :
Failure of a capacitor
Failure of the contactor
Failure of the delay timer (precharge resistor beeing used to long)

Usually we change everything because the parts cost is over all lower than the labor and production lost.

I would check the main contactor. If it has some contact problems, it might be the cause.

Oddly enough, at some point you will have to try to start it and maybe blow more things.
I don't know about 2012 Leaf but the 2013 had a serie of bad heating resistances. They had to change ours when we bought it used last year (I don't know how the previous owner survived!).
 
gugusse said:
Hello,

At work we have some precharge resistors on capacitors or large motor line.
Sometimes they burn, the reason can be multiple :
Failure of a capacitor
Failure of the contactor
Failure of the delay timer (precharge resistor beeing used to long)

Usually we change everything because the parts cost is over all lower than the labor and production lost.

I would check the main contactor. If it has some contact problems, it might be the cause.

Oddly enough, at some point you will have to try to start it and maybe blow more things.
I don't know about 2012 Leaf but the 2013 had a serie of bad heating resistances. They had to change ours when we bought it used last year (I don't know how the previous owner survived!).
Gloves and wool blanket
 
Nubo said:
I understand the purpose of a pre-charge resistor, but don't know how it's implemented in LEAF. I would want to know whether the resistor is always in the circuit or if there is a relay or contactor intended to remove it from the circuit before the main contactor closes. If so, then perhaps the precharge relay is stuck closed.

Insight is provided here; http://www.mynissanleaf.com/viewtopic.php?f=30&t=21776&start=10#p525611

Step 1 is to try to find out from previous owners (invest some time in this!) what may have happened. Your error codes are consistent with either the precharge relay driver (in the VCM) precharge relay, precharge resistor (both in the battery) or inverter capacitor (obviously in the inverter) having blown. This can be caused by anything from somebody trying to add an extender pack and accidentally shorting the relay wires to gross HV bus mistakes. Depending on what happened, the fix may be as simple as replacing the resistor or relay to having to find a new HV/body harness.

Remember, the basic max continuous voltage that can be applied to the 30 ohm (40W) resistor is 35 volts, i.e. without considering its mounting
and overall thermal resistance to ambient. With HV, e.g. 375V+, mis-applied, the 30 ohm resistor functions basically as a fast-blow fuse for
connection times of just a few seconds. It would be helpful if the circuit diagram of the resistor were posted.
 
Nubo said:
I understand the purpose of a pre-charge resistor, but don't know how it's implemented in LEAF. I would want to know whether the resistor is always in the circuit or if there is a relay or contactor intended to remove it from the circuit before the main contactor closes. If so, then perhaps the precharge relay is stuck closed.

Normally it's just on for a second or two. There is the possibility that the precharge contactor has failed short. Path of least resistance should mean not much current (theoretically none) would go through the resistor with the main contactor closed, but maybe a small residual current is enough to cause failure?

Strange problem. :|
 
JeremyW said:
Nubo said:
I understand the purpose of a pre-charge resistor, but don't know how it's implemented in LEAF. I would want to know whether the resistor is always in the circuit or if there is a relay or contactor intended to remove it from the circuit before the main contactor closes. If so, then perhaps the precharge relay is stuck closed.

Normally it's just on for a second or two. There is the possibility that the precharge contactor has failed short. Path of least resistance should mean not much current (theoretically none) would go through the resistor with the main contactor closed, but maybe a small residual current is enough to cause failure?

Strange problem. :|

So without a schematic, the source of the problem is conjecture.
 
I inquired about upgrading my account to be able to post the picture of the service diagram, but haven't gotten a reply.

After finally getting up the nerve to turn on the heat and A/C to check if the precharge resistor would blow again, I heard the A/C compressor struggling and making a slight squealing sound, not similar to my 2012 Leaf. It turned off by itself after about 10 seconds. Worried I blew it again, I checked and the car still turns off, and on, goes into drive and reverse unlike when the precharge resistor was blown.

So putting the puzzle together, the previous owner was using the A/C defroster to clear the window this last winter. She came out to the car after 20 minutes had passed and the car would not go into drive or reverse, charge, or heat or defrost the car. Did all of the diagnostic flow charts from the service manual and upon advice from Mux, tested the precharge resistor in the battery junction box in the traction battery and verified the precharge resistor was fried. By the way, Thanks Mux for helping from long distance!

Maybe the FAILING High Voltage A/C compressor had put a large load on the precharge resistor and caused it to burn out? Would the HV compressor come on if it didn't have enough refrigerant? I wouldn't think so. Also, I read that these electric compressors must use a different oil than a regular conventional PAG compressor oil or it will cause it to fail. It calls for ND-11 ester oil made for electric compressors.

I will have my brother put some gauges to the A/C lines to verify refrigerant, but I suspect the compressor was the culprit. Anybody concur?
Should I have the compressor oil tested? As soon as my upgrade to Gold is active, I will post the wiring diagram.
 
Based on my very limited knowledge of AC systems, I think the compressor's only feedback is pressure (high side, low side or delta between the 2). I don't know of any way it could be made aware of the amount of refrigerant in the system until it was trying to pressurize it.

It's possible a seized compressor would overload the pre-load resistor but that depends on a lot of factors. It certainly is suspicious and without a detailed understanding of all the circuits and firmware involved, is a good suspect.
 
Since no schematic has been posted, I'll surmise what occurs:

1. Since the power rating of the pre-charge resistor is 40W, the max continuous current is about 1.15 amps (30 ohms).
2. Transient suppressor/integrator capacitors (10s of ufs - 500-600V) are used across (parallel) the down inverter and motor/motor ECU.
3. The 30 ohm resistor is used to pre-charge the suppressor capacitors (Cx) before the HV battery relay is switched on to the
elements of #2 above to avoid excessive battery transient currents. The time to charge the capacitors is less than a few seconds;
3 TCs (3 X 30 ohms X Cx)
4. If any continuous load (> 1.15 amps) exists while the pre-charge relay connects the pre-charge resistor between the HV battery
and the load (#2), the pre-charge resistor is destroyed.
5. There most likely exists a test to determine if the pre-charge voltage of #3 equals approximately the HV of the battery.
If not, the system fails to allow the vehicle to enter the start mode, i.e. the Cx wasn't pre-charged and the HV main relay
is not activated.

Hopefully others will provide a schematic and/or correct/supplement the above.
 
lorenfb said:
There most likely exists a test to determine if the pre-charge voltage of #3 equals approximately the HV of the battery.
If not, the system fails to allow the vehicle to enter the start mode, i.e. the Cx wasn't pre-charged and the HV main relay
is not activated.

Yes, there is. The motor inverter monitors the voltage of the main caps and permits startup when they start. From page 37 of the "EVC" manual for 2012's:
CONTROL FLOW
To connect the high voltage circuit, VCM first activates the system main relay 2 and pre-charge relay. As a result, the high voltage power is supplied to the respective systems via the pre-charge resistor in the pre-charge circuit. When the condenser inside the traction motor inverter is fully charged by the applied power, the traction motor inverter transmits a high voltage power supply preparation completion signal to VCM. Receiving the signal, VCM activates the system main relay 1 and deactivates the pre-charge relay. Then, normal power is supplied to the respective systems.
 
JeremyW said:
lorenfb said:
There most likely exists a test to determine if the pre-charge voltage of #3 equals approximately the HV of the battery.
If not, the system fails to allow the vehicle to enter the start mode, i.e. the Cx wasn't pre-charged and the HV main relay
is not activated.

Yes, there is. The motor inverter monitors the voltage of the main caps and permits startup when they start. From page 37 of the "EVC" manual for 2012's:
CONTROL FLOW
To connect the high voltage circuit, VCM first activates the system main relay 2 and pre-charge relay. As a result, the high voltage power is supplied to the respective systems via the pre-charge resistor in the pre-charge circuit. When the condenser inside the traction motor inverter is fully charged by the applied power, the traction motor inverter transmits a high voltage power supply preparation completion signal to VCM. Receiving the signal, VCM activates the system main relay 1 and deactivates the pre-charge relay. Then, normal power is supplied to the respective systems.

Thanks for the info. So hopefully nothing in the traction motor inverter circuitry, or any other load, can result in the pre-charge current
being greater than an amp or the pre-charge resistor will be damaged. Obviously a delay in the VCM de-activating the pre-charge
relay, or its hanging, could be problematic. You've have thought that the pre-charge resistor would have been fused, i.e. given the
complexity to replace it or a worst case failure mode analysis. Its failure, notwithstanding a DIY effort, is very costly as previously noted.
 
What did you all say? Sorry, its a bit over my head. We are soon to install an a/c compressor with of coarse the appropriate ND-11 compressor oil when I get my hands on it.


I have left messages with two moderators and haven't gotten a response about updating my account to post the diagrams and pictures.
 
Used to be that you put your photos and diagrams on a site like shutterfly, then linked to them here. Does that not work anymore?
 
We turned the A/C on again and the sounds coming from the compressor were consistent with my 2012 parked alongside. It's unknown to us why upon initial startup it sounded different other than the air conditioning hadn't been used in 6 months.

An A/C gauge set determined the pressures were nearly identical to my 2012 running at the same time on the same fan speed and cabin temperature.

After driving the car in 90 degree temps for about a week and with the A/C on, everything is all good again.
 
I have another confirmation of the association of these codes with the failure of the pre-charge resistor. I bought an immobile 2011 Leaf with a 100% SOH traction battery. After dropping the battery and removing the main relay box, I determined that the resistor was open. I replaced it and the car is completely functional. The initial cause of the failure is unknown to me, but a new resistor resolved the problem. Clearly Nissan didn't anticipate this part to be a common problem or they would have located it outside the traction battery. It's a cheap fix, but certainly not in terms of the labor involved.

Now, how can a 2011 still have a perfect battery after 70K miles? I saw no evidence of it ever having been replaced when I was under the car.

Answer: After driving the car for 40 miles, I discovered an inconsistency between the battery display and regeneration behavior and the initial 100% SOH reading. While it still shows 12 battery bars, SOH is now 60% on LeafSpy. It appears that a service tech did a BMS reset in an attempt to fix the error codes the disabled car was throwing, and, of course, was unable to repair the pre-charge resistor that way. I'll swap in another traction battery in a few weeks.
 
If the pack isn't brand new, then there's zero chance of an SOH of 100%

Almost certainly, the BMS was reset and you won't know the real SOH unless you:

  • Road test to verify the useable range
  • Estimate the capacity by running down to 20%, L2 charging to 80%, then multiplying the kWh reported by the EVSE by 1.67 to estimate the capacity
  • Wait for the BMS to recalibrate
 
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