MontyPyFly

I've been chasing an intermittent Parasitic draw for months now. (2009 JK 2 door Auto) Finally got it to draw while I was testing and tracked it to :

Fuse M28 10 Amp Red Next Generation Controller (NGC), Transmission Feed (TRANS FEED), J1962

So in my mind it has something to do with how the shifter (auto) get into park, or something. I got the draw to appear after Shifting into N and then P again. This makes sense for an intermittent problem, if something is shorting out with the physical movement of the shifter, right?

Or not right? Was this a coincidence? I don't know, and after a 60 degree day here today, it is now starting to snow tonight and will be all day tomorrow, so I'm not going to be out looking for physical wireing issues tonight or tomorrow.


What I was hopping to get from all you knowledgeable folks here, is what does that M28 fuse actually go to? What/Where is the NGS and is the TransFeed actually referring to the shifter and transmission, or just the Computer?

Anyway, after hours of searching, at least I got to test the draw when it was actually happening (.41 amps when happening, .039 when acting properly)

Worst case scenario, I'll hook up a low vt LED light in line with M28 so I can wiggle the shifter until it goes out :-D

Thanks for any info

ronjenx

Are you doing all your testing with the meter in series, AND after letting the computers go to sleep? It can take up to 20 minutes.

If you are taking readings right after connecting the meter, the computers will not have gone back to sleep.
Moving the transmission lever from park may reawaken the computers.

MontyPyFly

Yes, I let the computers go back to sleep every time. Moving the shifter awakens the computes and draws .65 amps (actually turning the key so you CAN move the shifter awakens the Computers)
All tests with Digital Multi-meter at Milliamp settings. Inline on Neg Cable.
I have been doing this for months :-P
I just need to get some ideas of what and where to check now that I have the M28 fuse isolated as the cause.

ronjenx

From what I can see in the diagrams, M28 goes from the battery bus directly to the Powertrain Control Module. I see nothing else on the circuit.
There are at least 30 items connected to the PCM that could draw power through it.

Are you looking for a parasitic draw because your battery goes dead in a short time?

MontyPyFly

Yes, It goes dead some times. The battery can go down to almost nothing in a matter of days, and other times it can go months.
Does your diagram show which plug it goes to on the PCM? I can test each wire in the plug to narrow it down to a specific colored wire and see if I can find out more what is causing the draw from that if I can find the wiring diagram of that plug..(or I can test all wires in all plugs if necessary.)

ronjenx

What year is the JK you are working on? There is a difference between pre- and post- 2012.

MontyPyFly

ooops, I should have said: 2009

ronjenx

OK. I don't have a 2009 wiring diagram. If it's like my 2008, M28 gets power from the RUN/Start relay, not the battery bus as the 2012+ diagram shows.

The RUN/Start relay should be cutting power to M28 when you turn the key off. If you have a draw through M28 with the key off, maybe that relay is not opening when it should.

MontyPyFly

Interesting idea, however I think that a bad run-start relay would be detectable by something more dramatic, like a no-start issue :-)
But I'll try anything at this point.

Update, The draw to showed up again and I pulled the start/run relay with no effect. I then pulled the 4 plugs on the PCM and the draw went away after pulling the last plug, closest to the fender, but when I plugged it back in, the draw was gone, so I couldn't test any of the 15 pins to narrow it down to a single wire :-(
But the fact that pulling plugs and fuses can "reset" what ever it is that is causing the draw, leads me to believe that the issue is not a frayed/shorted wire, or physical shifter issue, but is an electrical/relay/computer issue, As Ronjenx suggested (it being something not properly "turning off" whatever is causing the draw). so now I'm getting closer to finding something, but further away in the expanding number of possibilities.

ronjenx

Connector C1 is the one closest to the fender.

Pin Circuit Description (pin #, circuit #, wire gauge, wire color, description)

9 Z903 16BK/LG GROUND
10 A209 16RD FUSED B(+)
11 F202 18PK/GY FUSED RUN/START RELAY OUTPUT
12 F1 18PK/WT IGNITION SWITCH OUTPUT (UNLOCK-RUN-START)
18 Z903 16BK/LG GROUND
19 - - 20 G6 18VT/GY EOP SIGNAL
24 A804 16RD/GY GEN SENSE
27 F856 18YL/PK 5 VOLT SUPPLY
29 A209 16RD FUSED B(+)
31 K141 18DB/YL O2 1/2 SIGNAL
32 K904 18DB/DG O2 RETURN (DOWN)
33 K243 18BR O2 2/2 SIGNAL
34 D65 18WT/BK CAN C BUS (+)
35 D64 18WT/LB CAN C BUS (-)
38 F342 16BR/WTFUSED ASD RELAY OUTPUT