About a week ago this situation popped up: Only when I start up on a cold morning and need to cycle the grid heater the lightning bolt appears along with the CEL. As I start the truck there is a rapid "machine gun" sound for about a second, something like a relay making and breaking. The sound appears to be coming from inside the dash on the driver's side or perhaps just behind the firewall. It comes & goes so quickly I can't quite pinpoint it.

On the second start the lightning bolt goes out and the CEL extinguishes about 3 start-ups later. The code reads as follows:

P2509 Ecm/Pcm power input intermittent.

I also notice that while the grid heater is on the voltmeter reads fairly low, around the lowest black portion of the scale. Having had electrical background I'm diagnosing the problem as weak batteries (which may explain the chattering relay) but I'm presenting this situation to you guys for your diagnoses. The truck does start and run perfectly OK. Thanks in advance...

 

I know when my passenger side battery went south it caused all kinds of weird issues. Memory loss to odometer and overhead and fog light switch. Strange rapid clicking in the dash. No codes though.


Very possible that may be your problem isolate them and test individually and if so, replace both.

 

Back when I first got my truck in January of '08, this happened after using the block heater. The dealer did a re-flash and all was good. It was an issue with the grid heater. However your power output code would indicate a possible battery problem too.

 

Have you thought about taking the power away from the grid block and see if that helps? That would be my first step, Might have a problem with the grid block. If its faulty it might drain it down bad enough to cause it to throw that code.

 

Thanks for your suggestions, guys. I checked battery electrolyte levels today and all was good. Haven't found any loose connections, either (yet). The weather has been getting warm enough so that the grid heater hasn't been necessary.

Is it possible to get an ammeter reading on the grid heater to see if it is in spec? (I don't know what the amperage draw is supposed to be, anyway).

It could just turn out the batteries are getting ready for replacement. Is average life expectancy 3 years? I would expect more but this is my first diesel and first vehicle with 2 batteries.

 

What you're experiencing is perfect normal with respect to the readings on the voltmeter. The grid heaters do pull a ton of amps when they operate.. in around the neighborhood of 150 amps. The chattering you're hearing is most likely the relays performing their normal function in cycling the heaters.

As for your error code (P2509), since it went out in 5 cycles (startups) or less, it is a soft code and not a major fault in the ECM or sensors. You should definitely mention it next time you take your vehicle in for servicing at your dealer, but it's nothing to be overly worried about. Your batteries should give you in around 7-10 years of service under normal use. This would be lessened if you live in a climate of extremely cold winter months.