Hmm my '18 CTD just did the same thing about 3wks ago and yup P2509 and with the 8ish volt dash reading. It happened about a year ago. When it happened then, I checked the fuses and noticed that 90% of them were sticking up a bit. I pushed them all down and it started. This time when it happened, I pulled them out and put them back in and still didn't work. So I had the sucker towed to the dealer. ($235) It first came up with "Service 4wd system" then the single click as you described. Both my batteries also tested "good". Took the truck to 3 different places for testing. But it looked like they were using the same tester. SO I went to HF and got the analog tester. When I test them 1 tests nice and strong, the other one will test on the low end of load range. (just barely below the 800amp line).
After thinking about it, I had my bro-in-law meet me at the dealership and jumped it. That's when I went to the 3 parts places for testing. It had been cold the previous night that this all started, so I did about a 150 mile trip to throw on a charge. And then for 2 nights I put it on a battery charger/tender and when starting, the voltage would drop to 9v but started.
Soooo I went to Wally World and got 2 new batteries. This time I stepped up to the AGM ones for $340ish for both. The core charge is $12 so I kept both. I put them both on spare battery charge/tenders and they both go to "green". The one still tests on the low range of the load test.
With all the computers and crap, it seems that the computer tries to do all it's monitoring and shuts down if the voltage drops while cranking. There is no more rapid clicking of the starter solenoid to give the sign of a low battery.
If we get a decent day, or wait until spring, I will be looking at the starter cables, corroded connections, grounds and all that good stuff.
Cummins P2509 Engine Code
When you scan your Dodge/Ram Cummins engine and receive a P2509 diagnostic code, it will read ‘ECM/PCM Power Input Signal Intermittent Code’.
P2509 appears on Cummins engines when there is an electronic signal being sent to the ECM/PCM that is faulty or intermittent. Electronic signals are measured within parameters, and when the signal falls outside of the parameter range, the Power Input Signal Intermittent Code P2509 is thrown.
A Cummins P2509 engine code is a battery related issue. Either your battery is weak and running low voltages, something is draining your batter faster than it can charge, or there is a poor electrical connection. While all signs point to the battery, this trouble code can actually be caused by a number of issues, and replacing the battery isn’t always the answer.
