2019 Hino 338 power issue

psy

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Hello, I am trying to figure out what happened with my Hino. The original batteries that came on the truck were shot, I had to jumpstart it yesterday to finish the day and ordered the new batteries. This morning I replaced them with the new ones and put everything back together. When I turned the key, it was like there was still no power however the dash beeped 3 times paused and then twice more (unsure if related or code) the power locks are working so I think one of the fuses blew while working on it. I was told a member here, greasy t-shirt might be able to help because they are a Hino mechanic. I appreciate any tips and tricks that may help me come to definitive explanation for this. Thank you!
 

Hino123

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Welcome. First rule of hino is check EVERY fuse. Start in the fuse relay center in the cab. Then check the fuses in the external relay box above the batteries…& there is also another external fuseable link box to the side of the air filter housing. The larger amperage fuses have a clear cover so you can see if the fuse is blow. These can be hard to see as sometimes it is a small break. Look them over closely. If all the fuses check out make sure you have good contact on your battery connections… the positive side especially. Make sure you did not leave any connections off or loose. If it is doing weird things that it was not doing before. I would start at the battery connections. I see it all the time people leave one terminal not connected. Start there and report back.
 

psy

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Thank you for your reply. I think my game plan tomorrow will be to check all the fuses and since fortunately I have two other running 338s I can borrow parts that I know work to test. Should I disconnect the battery before trying to remove fuses from one of the other trucks? I definitely can't put another truck out of service for the day, and I really hope I can figure out what fuse or replacement part is needed - and that it's in stock nearby!!
 

Hino123

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You don’t have to remove battery connections to remove fuses. Unless you are removing the high amperage fuses. Some of the large amperage fuses have constant battery power on them so you will need to be careful as some of them are held on with bolts. Anything in the cab relay/fuse center would not require battery cable replacement. A word of caution ⚠️ be sure to label or make note of anything you remove or swap. Playing “musical relays” can cause a host of issues if you do not pay close attention to what has been swapped. You don’t want to create any additional issues.
 

Hino123

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DO make sure the key is off when removing fuses or it can set fault codes.
 

psy

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Thanks for the help again. I just checked 90% of the fuses and they were all good but ran out of time to do anything else right now. The two 10a ones on the far right in the cab fuse box marked "spare (ign-1&2)" were blown but not sure if that's the cause as I replaced them and the issue is the same. I'll try cleaning up and reinstalling the connections tonight and hopefully have more luck.

Is the beeping when I turn the key worth noting? It's the only thing that happens when turning the key, otherwise looks like it's dead as before besides being able to cycle the door locks now. The beeps are coming from the cab fuse box when I turn the key to ignition and the pattern is 3 faster beeps, pause, 2 short and spaced out beeps, pause, then the 3 faster beeps again. The only other time I ever heard the beeps from the dash is when hitting large bumps in the road while driving.
 

greasytshirt

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I'd definitely revisit the battery connections. There are at least three wires connected to the positive side and it's very easy to overlook one and leave it disconnected.
 
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Hino123

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Beeep beeep beeep sounds like a derate from the SCR. Are there any lights on or flashing in the cluster? Sounds like loss of power to the DCU. Pay close attention to corrosion in the smaller ring terminal connections on the power side. One of these feeds 12v to the DCU (SCR computer)
 

psy

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So I'm working on the truck today (happy holiday everyone) and got my voltmeter to check what's going on again. The batteries are hooked up correctly and power is definitely getting to the truck. And all the connections are made and working. There is power going to a few fuses but not to the main 100a or 80a in the fuse box right above the batteries. From here I have no idea what steps to take, so thank you guys for your insight
 

psy

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Actually, if I put the positive lead of my voltmeter on the positive lead on the battery and the negative lead on the wires feeding the 100a fuse and 80a fuse, it shows 12.7v, so are these fuses actually grounded? Does this all check out so far?
 

Hino123

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Do you have source battery voltage on both sides of the 100a and 80a maxi fuses? This would indicate you are getting power to & through the fuses.
 

greasytshirt

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I'd get a look at the blue/black wire connected directly to the battery (may have to pull insulation back to identify it).

It goes directly to the 100 amp fuse.

Maybe the ring terminal is corroded at the crimp.
 

psy

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Do you have source battery voltage on both sides of the 100a and 80a maxi fuses? This would indicate you are getting power to & through the fuses.
I think I was only checking the battery side, and unfortunately I've had to stop working on it for now to start the workday. I did get a pic of the connections though. The lead on the positive side of the battery closest to the camera goes to a 80a in line fuse which I checked. The lead on the other battery is on but I don't know where it goes.
 

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psy

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I'd get a look at the blue/black wire connected directly to the battery (may have to pull insulation back to identify it).

It goes directly to the 100 amp fuse.

Maybe the ring terminal is corroded at the crimp.
I think I will just swing by the bay really quick and try this, however, why would the wire connected to the 100a have the polarity reversed? When I was checking voltage with the negative lead on the battery negative post and postive on the wire to the fuse, I was getting nothing. I decided to switch to continuity and got -770, which is why I switched the leads to the positive side on the positive battery and the negative on the wire to the fuse, then got 12.7v. I'm not the most electrically knowledgeable but I thought this was very strange.
 

psy

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So my boss actually went ahead and got a mechanic to come out and take a look at the truck. They verified that all the connections were in place properly and that we were getting power at the starter but there is no power inside the cab whatsoever. He remarked the strange polarity reversal at the 100 and 80 fuses in the fuse box above the batteries (the other fuses in the same box did not have this issue) and had no idea what's causing all of this. He said he'll need it towed to his shop to really dig in a find out what's going on but I am holding on to hope someone may have some insight of what could have possibly went wrong here before biting that bullet.
 

Hino123

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Let’s back up. All of this started happening after you replaced the batteries. I suspect either someone jumpstartes the truck by connecting the leads backwards & blew a fuse. Or there is a connection not connected. The picture of the batteries looks good however… the connection on the positive front battery is not an OEM connection. That means the cable end has been replaced. Or it is still missing one connection. The original terminal would have been a round ring terminal, and that is a flat copper terminal. The wires are very short and to have it connected the way it is suggests it has either been repaired/leganthened or it is for a lIftgate or other item. If it was repaired I would carefully inspect the repair connections. As far as the reverse polarity thing. It doesn’t make sensible my head. If you connect the negative lead on your meter to battery ground and the red lead to the 100a and 80a fuse you should have power on both sides. If you don’t there is an issue there somewhere. Also be sure to check the fuse “cab b + power” in the in cab fuse panel. If this is blown the cab will not have power.
 

psy

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You were right, there was a missing connection to the leads. I couldn't even tell from the picture I took nor did I notice taking it off, but there is an all black wire that I left unconnected. Unfortunately I have no idea where it goes. An earlier reply mentioned 3 wires that all go to positive, so I'm guessing it just goes on positive like the only other two I have. Wish me luck
 
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