POWER DRAIN PCM B 20amp fuse under the hood

[joeracer01]

PCM B 20amp fuse under the hood

What is this for?
Why would it be causing me to have a electrical power drain?
Batteries are new
Doing a parasitic battery drain test when I pull this fuse multi meter shown almost zero mA pulled.

 

[JoshH]

It supplies battery power to the ECM.

 

[Kappa9012]

how long does that circuit stay hot for after you key off?

 

[JoshH]

how long does that circuit stay hot for after you key off?

It's always hot.

 

[joeracer01]

Well it seems to be the culprit.
I pulled the fuse and battery is staying stable.
Any ideas why its drawing so much power?

 

[JoshH]

No idea. Maybe a problem with the ECM. How much current is it drawing?

 

[joeracer01]

127mA

 

[dmaxbowtie]

This could be toatally irrelevant but does that only supply the ECM? I've heard of a few instances where the power seats or power seat module?? Were the culprit

 

[Kappa9012]

where are you pulling your current reading from? I have an ammeter and I could check to see what it normally is.

 

[Chevy1925]

.127 amps should not kill 2 batteries over night...

 

[JoshH]

This could be toatally irrelevant but does that only supply the ECM? I've heard of a few instances where the power seats or power seat module?? Were the culprit

From what I can tell, it powers the ECM and supplies voltage to the coil for the FICM relay.

.127 amps should not kill 2 batteries over night...

That's what in thinking too. Maybe a month, but not overnight.

 

[Chevy1925]

The cop car systems I worked on pulled more amperage once all off to keep the power tamer (electronic switched that shut all of the aftermarket setups off), fire suppression system, and camera system all ready and working. Those things after everything off would still pull .5 amps and even after a week of sitting in the shop yard would still start right up.

 

[Kappa9012]

batteries weak???

 

[JoshH]

batteries weak???

First post says they're new.

 

[Chevy1925]

Doesn't mean they aren't crappy or bad as it is

 

[Kappa9012]

First post says they're new.

Sweet jesus my eyes suck...

 

[mzman1968]

I'm having a similar problem. Just bought two new batteries and didn't use truck for a couple of weeks and both are ruined and I never even drove the truck. I tested both batteries after I bought them and they were fine.

Any ideas or suggestions to find what's draining the batteries? Anyone else experienced this?

I was thinking of buying a battery disconnect switch. Specifically a Moroso Super Duty switch with a 300 continuous 3000 peak amp rating. I have looked at a schematic and it shows both positive battery leads connect at the starter. Does anyone know if I can buy only one switch and connect it at the starter or would I have to buy two switches for each battery?

Thanks

 

[joeracer01]

Finally solved my power drain problem…

Had a professional diagnose it and said the ECU was doing it.
So I replaced the ECU… DIDN’T HELP!
Disconnect the alternator… still no help.

I finally removed the power cable going to my glow plug controller. I have a California truck and the GPC has its own box to distribute power to the glow plugs. 49 state trucks have it all built into the intake heater relay. So it’s been 5 days and the battery has stayed stable with little to no voltage drop. The crazy thing is I have been doing parasitic battery drain test from time to time and could not see this drain even. I thought it was the PCM B fuse but wasn’t.
I have killed so many batteries (good thing for 3year free replacement) and had to add a battery switch to one battery so I could protect it from the drain and start my truck when needed without a jump start.
This issue has been here for 4 years. Glad it’s finally over. Trying to decide if I should buy a new controller as they cost around $200 but not needed to start the truck at all just have to deal with seeing the CEL P0380 and resetting it constantly, but no more dead batteries!!!

 

[juddski88]

I would just buy a known good one from someone parting out an engine here. Or check partszoneonline.com for a better price new.

 

[Bob H]

I have an intake heater relay box - 49 state truck. Not sure if that helps? I'd do $40 shipped for it. Was a 2003 LB7.