Parasitic draw TCM (EATX)

[DaddySS]

I bought a nice 2002 Liberty Limited for my daughter and have done a number of repairs to bring it up to spec - motor and transmission mounts, upper control arms, coolant flush, differential and transfer case fluid change, water pump, Idle and tensioner pulleys,etc. and for my final bit of repair, I'm analyzing a drain the battery that kils it after about two days. I see a 98 milliamp draw and have narrowed it down to fuse #5 in the power distribution block to the TCM. Have you seen similar issues, is there a common problem to look for or do I need to go step by step to isolate the problem?

 

[Billwill]

A draw of 98 ma is a bit much...needs to be around 30 ma. with Radio OFF, all doors closed and internal lights turned OFF.

You obviously know your way around checking parasitic current draw...download the 2002 Jeep KJ Service Manual below if you do not already have it....section 8W has the wiring diagrams.

Wires scraping through to chassis/ground are getting quite common now days as these Jeeps of ours get older!

I will look through the diagrams tomorrow...bedtime here now...and see if anything jumps out at me.

I have had plenty wiring problems on my RHD 2002 Export 2.5 L CRD after a front collision damaged a large wiring harness up front....within a square metal tubing. I do not think the LHD/gassers have the wiring loom going under the radiator up front.

End result was that with any suspect circuit I had to completely isolate all ends by unplugging components and cutting off all ends of the circuit...including splices...so that this section of wiring was now hanging in mid-air.

If I got any resistance reading of this "floating" wire section of wiring to chassis/ground then it meant that the wire in question was shorting to chassis or shorting to another random wire within the harness.
In this case I would cut out the complete suspect wire...insulate all ends..and replace with new wiring...this time taking the shortest route and not going around the whole engine bay.

I definitely had instances of shorts or semi shorts to other wires sometimes!

I have now fixed about 13 bad wiring circuits. I have marked my changes on the relevant Wiring Diagram pages and left these pages inside the Jeep for any poor future Buyer of mine to find!

www.colorado4wheel.com/manuals/Jeep/KJ/

 

[Billwill]

OK if you have downloaded the 2003 Jeep KJ Service Manual Page 8W-10-17 shows Fuse #5 output is a Red/White wire splitting at the fuse socket and going to the Transmission Control Relay, Transmission Solenoid 42RLE and Except 42RLE and the TCM.

Most of these go through connector C105. The Component Index gives you the location of Connector/Splice/Ground points..sometimes with pictures.

So if you remove fuse #5, and the TCM Relay nearby and disconnect C105 then the top section of this Red/White wire should be floating.

Re-plug the C105 connector and disconnect the Transmission Pressure Switch connector and the TCM connector and the whole of this Red/White wire should be floating....if not then this wire is scraping to chassis/ground or another random wire somewhere.

If the wire does not seem to be conducting to chassis then connecting the connector back onto the TCM or re-connecting the Transmission solenoid will obviously give you some....but not too much... continuity reading to chassis.....maybe the solenoid is faulty...hopefully the TCM is not faulty!

There is a Fuse #12 shown there before Fuse #5 for "Security A/T" whatever that means...this fuse slot is probably empty.

If you do get some reading to chassis when all items are disconnected then you need to physically trace the wires to look for any damage to the insulation. If it is not possible to access these wires in some of the branches then you need to cut off all ends in that branch and fit new wires!

I am going to state the obvious here....in case other readers here want to perform this type of testing using the Multi Meter in OHMS mode....do not touch the meter leads with bare hands...your internal resistance affects the reading!

 

[DaddySS]

BillWill: Thanks so much! I was looking at the same thing - the wiring to the pressure sense switch appears to be a straight run. When I probe all the pins on the TCM there is .5V draw with key off and removed, doors locked etc. I see the 12v to the TCM naturally since it's fused from the power distribution block but I wouldn't think the TCM should show a voltage to the line pressure sensor? I'm going to get under there tomorrow and disconnect/have a look at the wiring. Another odd symptom that I can't quite get a handle on, if I interrupt battery voltage momentarily, the draw drops to 9mv, as though a some relay or circuit hangs from the "ignition on" cycle and only releases with power interrupted.

 

[Billwill]

The TCM is never completely OFF....it runs quietly in the background checking that the doors are not being forced open and the tasks but all items including the Radio keeping the time should only draw about 30 ma while switched off.

You will need to disconnect the battery and use the OHMs setting on the Multi Meter to check that once you have "floated" a suspect section of wiring ie. no components are connected at any end..including where the line gets spliced elsewhere.

Or you can leave the battery connected and with meter set or DC Volts place the meter negative lead to chassis and the positive lead to the "floating" section....if the floating section is not connected anywhere you do not expect any voltage!

I agree that there may be some relay energized that only drops when voltage is removed...off hand I do not know of any relay that should be doing this!

 

[DaddySS]

My thought was this: If it's drawing then either something in the TCM is not properly sleeping or a connected component which should drop to normally open is hanging or shorted?

Thanks again, I'll see what kind of testing I can get done today and post updates.

 

[DaddySS]

With just the 12v feed on pin 56 connected to the TCM there's no draw so that at least eliminates an internal short.I 've disconnected all the sensors an relays except two - the solenoid pack and cranks position sensor with no result, I'll tackle those tomorrow.

 

[Billwill]

With just the 12v feed on pin 56 connected to the TCM there's no draw so that at least eliminates an internal short.I 've disconnected all the sensors an relays except two - the solenoid pack and cranks position sensor with no result, I'll tackle those tomorrow.

Sounds good...if pulling off the sensors/solenoids does not drop the current draw then you need to look for a wire shorting partially to chassis/or to another random wire.

 

[DaddySS]

Update, and next steps. It had been either dropping to 98 mv or dropping to 8mv with the draw eliminated. After disconnecting the TCS pack and the crankshaft sensor, the draw was still there. I noticed that the cooling fan was making an audible sound (very slight thump) when battery power was reconnected so I disconnected it - the thump went away but but not the draw. I continued looking at the fan relay, the battery temperature sensor, etc. and now here's where it gets interesting. I looked up at the meter and the draw was gone, so now I started reconnecting one by one and no draw - cycle the ignition to on each time, and after about three minutes for the systems to sleep it dropped to 8 mv. Now thinking that there were too many changes for a vaild system test, I dropped it from the jackstands, buttoned it up and took it for a test drive. When I got back, the draw was there except at 100mv, not the 98 I had been seeing. I figured it's time to restart my tests.

In the meantime, I read in the repair manual (thanks very much for link) in the battery section for IOD where it states that the time for the TCM to sleep is 20 minutes.

So while I was looking around and doing some tests, I look up and notice the draw is gone. Now I'm thinking it wasn't anything I was touching, it was 20 minutes. So I cycle the ignition and start a 20 minute timer on my phone and sure enough at almost exactly 20 minutes the draw drops.

Most of the testing I had done earlier was beyond 20 minutes, so now I have to conclude that resetting the connections or the multiple resets to the TCM and PCM have eliminated the draw but which? Testing continues this week.

 

[Billwill]

You obviously are teasing us when you refer to the draw dropping to "98 mv" and not "98 ma"

There is a good chance that by re-plugging things and moving things around that the problem has resolved itself...I have spent hours tracing problems and then suddenly everything is working just fine!

You will need to remove one connection on the battery and insert the Amp Meter in series with it and monitor the drain over time to see if it changes...obviously do not try start the Jeep or you will blow a fuse in the meter or blow up the meter!

If disconnecting all solenoids and other components does not drop the current draw then you have no choice but to start cutting wires off at all ends including any splices and see if drain is gone and check for any continuity to chassis while battery is disconnected. If there is a problem with that installed wire then replace the wiring with a new wire!

Hopefully you are at a stage now where the draw is low enough after a 20 minute wait and the problem does not return!

 

[DaddySS]

Update after a couple of weeks..... Since the draw was now gone, and I have to deliver the jeep back to my daughter, I didn't have the luxury of "wait and see" so I took the shotgun approach and replaced the things that had shown unexpected or unreliable results. Looking at the schematic for the TCM - where the 4mv drop (98ma) was occurring and and the fact that after disconnecting the transmission connections the indications varied - I replaced the TCM, Transmission solenoid pack, cooling fan relay (remember the thump from the cooling fan when the battery was connected), pressure and input and output speed sensors, and the transmission control relay. Since the alternator bearing was making noise anyway, I replaced it too with the mopar OEM. With all of that I have tested for 7 days now and the battery voltage drops .05 v per day which means it'll lose one volt after 20 days. I'm bringing it back to her on Saturday with a good level of confidence.

 

[renegade 04]

The one thing that definitely causes issues with a parasitic draw is a bad ignition switch. My jeep is on its 3rd ignition switch.