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Multiple DTC's C1858-72, C1851-18

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3.8K views 2 replies 2 participants last post by  2006RD7CRV  
#1 ·
Hi Guys,

This is becoming a problem. I have a 2020 hybrid with 128,000 miles. I got these codes a few weeks ago. The AWD connects then turns off when these codes come back. It seems to reset when i turn the car off, then come back after about 100miles.

The fluid was changed first. then the codes came back and for the code C1851-18(lost communication with diff fluid pump):Circuit current below threshold. I saw here that the diff motor needs to be replaced. I just did over the weekend and both codes came back again. is it possible the motor is faulty?

What about the C1858-72 (Diff fluid pressure deviation high): Actuator stuck open? What part is this referring too? I don't have access to a Honda scan tool. The only thing I did not do is the Air Bleeding. I can't do it without a Honda tool.The fluid is fine and level in the rear diff. I did read about what air bleeding actually is.

What is the actuator in this diff? Maybe I can not find the info on here, or I'm typing this in wrong.

Can anyone help me out at all? I have not gone to Honda yet, they want 200 for first hour of diagnosis then i think it's 80 per hour after. I'm hoping there's a Honda tech on here that has seen/replaced these parts.

I made the codes in bold so they can be easily seen.

I appreciate anyones time.
 
#2 · (Edited)
Yes a Honda HDS would be nice but beyond the price of mere mortal men.

You have the meaning of one of the dtc incorrect. C1851-18 means low current in the hydraulic pump circuit (open circuit). C1858-72 means low fluid pressure, which would occur it the pump motor is not running due to an open circuit. This could be a simple electrical connection problem such as a ground connection. If you read the resistance across the motor it should read 10 ohm or less according to the service manual. However I also checked the technical service bulletins for your vehicle and found TSB 23-031 which may relate to your situation. It refers to the pump motor seal failure allowing fluid entering the motor housing causing either an open or short circuit. You might Google search this TSB for details.
 
#3 · (Edited)
Yes a Honda HDS would be nice but beyond the price of mere mortal men.

You have the meaning of one of the dtc incorrect. C1851-18 means low current in the hydraulic pump circuit (open circuit). C1858-72 means low fluid pressure, which would occur it the pump motor is not running due to an open circuit. This could be a simple electrical connection problem such as a ground connection. If you read the resistance across the motor it should read 10 ohm or less according to the service manual. However I also checked the technical service bulletins for your vehicle and found TSB 23-031 which may relate to your situation. It refers to the pump motor seal failure allowing fluid entering the motor housing causing either an open or short circuit. You might Google search this TSB for details.
Hi,

I appreciate your comments, I will look at that other TSB. Are you possibly saying that I replaced that pump motor for no reason?
Those codes that I put there with the description is what exactly it said on the reader I have.
The TSB for that C1851-18 says to put a new motor in. I hope we’re talking about the same part here cause if it’s a new motor why would it be leaking?

I put a photo of the part i changed below.

I’m sorry if this is confusing to me, but I’m trying to understand this.