Ask what codes are being pulled. The codes should be in the Pxxxx or Uxxxx format.Dealer wants to replace the tcm on my 2013 Hino 195h. It's 1000 bucks. The red atm light has come on multiple times going into the safety mode. After taking it in several times they have read the codes and not enough voltage.
The Aisin TCM is more robust, imo, than Allison TCMs. I doubt it's the TCM (but I'm not there to troubleshoot it either.
The first thing to do is load test the batteries and clean all connections. A crappy battery means low voltage during crank, which can set codes.
If the batteries are OK, I would check the resistance of the TCM's ground path, and voltage to the TCM. If this seems OK, I'd severely test the alternator (engine at higher rpm, carbon pile tester on batteries, maybe a 50 amp load for a minute or two to get it hot). See if voltage drops out after that. I'd also check to see if alternator is leaking A/C voltage. They don't like that.
The engine ECU on the little cabovers sometimes burn up the injector drivers but that's the only fault I know of with those.
Get the diagnostic codes.
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