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Hello everybody, i need some help regarding a Lexus Rx450h with the C1378 error.
This code popped out right after a check hybrid system, the error for the check hybrid system was:" lost comunication with hybrid Battery suply (029a-123)". I reset this code, managed to arrive home with the car and then the C1378 code start popping up along with the check brake system in the dash.
I checked the fused, i checked the brake power supply and the harness, at this point i do not know what to do anymore. I tried resetting the car by unplugging the Battery and using a paper clip for the 13 4 pins in the obd... still getting the error.
The cars abs esp, tcs, etc work fine, i tested them but the error is still present. At this point i do not know what to do anymore. From what documentation i found on the web, the skid ecu could be the problem but what bugs me is that all the safety functions are active and working properly. 
Can someone help me what to do?

Thank you!

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Have you checked the 12 V Battery voltage?  If never changed before, may be it' s a bit old.

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+1 for the 12V Battery.

When that starts to fail it can throw some weird and wonderful stuff at you.

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I am thinking at the 12v Battery to,I checked the voltage and it was 12,7, seems pretty good to me but i will order one tomorrow and see if i have any luck. Thank you for your answers.

 

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On the Prius, C1378 usually points to a faulty brake control power supply.

The BCPS manages the power fed to the high voltage Battery under regen braking. It is powered from the 12v supply and I believe it contains a capacitor or bank of them to manage the 12v power supply when the 12v Battery voltage drops, because it controls something essential like the brakes and needs a stable power supply. Don't want the 12v to drop and the brakes to disappear! If the 12v stays low for too long, the capacitors drop their voltage and throw a code. So the guys pointing to the 12v battery may be on the right track. The bad news is if the new 12v Battery doesn't solve the problem, then it needs a bit of nous and diagnosis to confirm the cause of the fault code. 

Not sure if this is all relevant to the RX because the systems may be different between the RX and the Prius (for instance the BCPS may be incorporated into the DC/DC invertor on the RX), but it sort of informs you as to what may be causing the system to complain.

 

 

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Delphius 1 you are right. I unplugged the bcps and nothing happend, same error so the bcps is faulty. I bought a new Battery today, the code is still there, i am wondering if those capacitors will regenerate if i drive the car or should i buy another bcps.

 

Thank you for your answer

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I'd try and run it a bit in hybrid mode and see if the capacitors are slow to charge up, then clear the code.

 

If the code comes back straight away then you probably need a new bcps. But do check related fuses like the ABS fuse to make sure it's not as simple as a blown fuse.

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I drove the car about 30 miles, nothing happens, code is still there and techstream can t delete it. I will buy a new bcps and see what is what.

The 12v Battery, before, when the brake pedal was pressed with the engine off the dome lights where loosing intensity, now with the new Battery they stay constant so it is good that i changed the Battery. I am sure all this mess started from that weak Battery.

I will keep you up to date how will i solve this problem, hopefully very soon and not something big of a deal 🙂

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Ok... i replaced the bcps... still getting the error, i do not know what to do at this point 😞

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That's a bit of a shame, doing the same on a Prius tends to solve the problem. Do you have access to Techstream at all? It may pay to get hold of it and start some deeper diagnostics.

Without the ability to delve deeper into the cars electronic systems, you won't be able to see what the issue is. The problem is all the various modules have varying levels of interdependence and if it's not the BCPS that's faulty you really need to know why its throwing the code.

Edited to add:

Has there been any water ingress at the back of the car at all? Any wetness around the electronic modules? Water can cause untold electronic issues if it gets amongst the hybrid Battery and control modules.

 

 

 

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Well... finally, problem solved! Man this was a tough one. Ok so apparently the problem was with a connector at the driver side,(mine is LHD). In every documentation of this problem that I had it did not tell anything about the driver side connector. I took of the panel of and apparently a blue plug right at the bottom was the cause. I had a friend who is an expert with electronics and after hours of testing saw that the harness is in short and traced a light green cable that was the cause. Then we traced the wire to the drivers side and managed to sort out the problem. Hope my experience helps others if they encounter such a problem.

The trace was even harder when the diagnose (techstream) pointed the BCPS as being faulty (error: c1378, sub code: 112).

Again i want to thank you all for helping me with opinions. So happy everything is ok now.

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when you said [mine is LHD] what you mean? where exactly is the blue plug? I'm having the same error code but have not touch any wiring hardnesss, believed maybe something got loose but I need to know where to go, where to start. 

 

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10 hours ago, franklyn said:

when you said [mine is LHD] what you mean? where exactly is the blue plug? I'm having the same error code but have not touch any wiring hardnesss, believed maybe something got loose but I need to know where to go, where to start. 

 

His car is Left Hand Drive (LHD) so his blue plug may be on the opposite side to yours.

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