Finally discovered the problem causing high IOD draw and a couple of sets of
Was about to change out the ignition switch .... pulled out fuse instead for
the Seat Belt Control module. This solved the problem. Seat Belt Control
module was back feeding circuit ACC 31 which was keeping the radio and
wipers on with the ignition shut off.
Anyone replaced one of these Seat Belt control modules? Cost info?
Did you also disconnect the wiring harness to the Central Timer Module to
verify that was indeed the cause of the backfeeding? It's accessible by
removing the panel below the steering column. It's the electornic box on
the right-hand side of the dash frame. Remove the two screws, and you can
pull the module out far enough to disconnect the electrical connector.
If it does need to be replaced, it's going to be a dealer job. Not because
you can't put a new one in (that's the simple part), but the new CTM needs
to be programmed with all of the features in your truck (power
windows/locks, keyless entry, steering wheel radio controls - all stuff like
Thanks for the heads up.
Didn't disconnect the CTM ... when I removed the fuse for the Seat Belt
Module killed the back feed to the wipers and radio as these are fed from a
common circuit ACC 31.
What would be the symptoms to look for if the CTM has failed?
Is the CTM feed from the ACC 31 circuit as well??
Okay - you should do that, and check the radio with it disconnected. You
want to make sure it's really a fault inside the CTM, and not a wiring
problem, or even some other component that's back-feeding the accessory
circuit. If you disconnect the wiring from the CTM, and the radio's still
energized, well - it's obviously not a problem within the CTM itself. After
that, I'd try the radio (disconnect it, re-connect the CTM, and see if the
wipers work with the ignition off).
Yes . it's got a couple of different power feeds into it... one is an
always-on feed from the battery, the other is the ACC31 circuit from fuse
Problem definitely is the Seat Belt Control module. Pulling the fuse that
feeds the SBCM solved the problem I was having with high IOD and killing
both batteries in about a week.
CTM is working properly.
Can't find this part (SBCM) listed at any of the online parts houses.
Anyone ever changed one of these modules? Any ideas on how much they are?
Okay, my mistake. In later years, all these functions were incorporated
into the CTM. However, in '99 (and probably earlier years, as well), there
is indeed a separate SBCM that handles these functions (seat belt switches,
solenoids, door ajar switches, etc.)
Have you disconnected the SBCM at the wiring harness, again to verify that
the SBCM is really at fault, and not the wiring? It's located underneath
the front seat center console.
Looks to be a little over $100 - I saw one quoted for $118.
Thanks for the info Tom! The saga continues ...
After removing the center seat I finally got at the Seat Belt Control Module
and disconnected it.
Checked for voltage again at fuse 16 with the ignition off. Voltage still
present at this fuse with the ignition key off. Fuse 15 that has a common
feed according to
the Service Manual is fine... no voltage present. Checked all other fuses
with the same feed in
the Junction Block, (6, 8, 10 and 15) and they are all at 0 volts with the
ignition turned off as they should be.
Looks like it is a Junction block problem. I notice the Service Manual
if this occurs the entire Junction Block has to be replaced ! !
Can only imagine how much fun it's going to be to replace the Junction Block
after removing seats to get at the Seat Belt Control Module.
Anyone ever changed out the Junction Block on a 99 Sport Quad CTD??
So let me get this straight... even with the SBCM unplugged, ignition off,
you get voltage through fuse 16. Are you saying that even with fuse 16
installed, you read 0 voltage on fuse 15, or are you saying that with fuse
16 removed, then fuse 15 shows 0 volts as it should?
If it's the latter, I'd strongly suspect a short in the wiring out to the
SBCM, before I'd suspect a bad junction block.
Not exactly, but I've done work behind the dash. It's actually not all that
bad... remove the 5 screws up on the top of the dash, at the base of the
windshield. Remove the steering wheel knee blocker panel, and remove the
steering column support. Rest the column on the seat, and loosen (but do
not remove) the two big hex bolts on either side of the dash, under the side
kick panels, that hold the dash frame to the body. Allow the dash to roll
forward, resting on the seat. You can then reach from the driver's side,
over the dash, and disconnect all the connectors from the junction block,
and remove it. Of course, disconnect the battery/batteries first, and let
the truck sit for several minutes to let the capacitators in the airbag
module bleed off.
I still vote for short in wiring myself, but that's just a percentage
Hi Tom !
With the SBCM unplugged the top of fuseholder 16 (fuse removed) is 13.6V
positive to ground ...the bottom of the fuseholder is 0.0V (fuse removed)
the top of fuseholder 15 is 0.0V to ground (fuse removed) and the bottom of
the fuseholder is at 0.0V. Same readings for all other fuses commoned on
this circuit in the Junction Block (6, 8, and 10). All fuses are fed from
the same source according to the SM diagram.
The kicker here is that if the top of fuse holder 16 is live with the
ignition key off ... they should all be live ... but they aren't.
If there is a short ... it is has to be in the Junction Block itself ....SM
says in this case that you have to change out the Junction Block.
Well that was fun ... stripped all the wiring harnesses under the seat...
examined all the wires ... wires all fine.
Examined all the connectors ... connectors all look fine...no signs of
overheating on any connector body or terminal.
With the harness all stripped I started probing around with a meter and
noticed each time I turned C303 in my hand the resistance would change
between the blue and pink conductors... pink conductor is from the IOD fuse
which is fuse 12. Blue conductor from fuse 16 is terminated in C303 right
next to the pink conductor.
Finally getting really frustrated with not being able to physically see any
defects in the wiring I decided to connect everything back up except for the
Seat Belt Control Module and put the fuses back in. Then to give the
circuit some load I turned on the windshield wipers with the ignition off
and turned C303 back and forth ... sure enough a mini light show going on
Bottom line is ... not a wise design choice to terminate both these feeder
conductors right next to each other in the same connector body.
Thanks for all your suggestions Tom ... much appreciated!!
PS Didn't order a seat heater with the truck but some options come for free
I guess! 8-)
Glad I could help out (and glad you didn't wind up changing out the junction
block). Seems to me the easiest fix would be to cut one of the two wires
from both sides of the connector (I think you mean C360, not C303 - but no
matter), solder a little extension on both sides, and use another type of
quick connector on it (I personally like the Posi-Lock connectors).
Aren't electrical problems fun to troubleshoot? :)
Another thing to help narrow things down... you've identified the circuit
that's getting back-fed - ACC-31, from fuse 16. Now you need to identify
which circuit is doing the back-feeding. Pull fuse 16, and fuse 12. Then,
check for continuity between the "load" terminals of each fuse (meaning the
terminal that feeds the circuit - not the terminal that gets +12V from the
If you get continuity, and I suspect that you will, you need to trace the
wiring out the the SBCM, and look closely at both the dark blue and the pink
wires. Also check joint connector #5, which is on the driver's side of the
knee blocker panel opening, inside the dash. If you disconnect this
connector, and repeat the continuity test above, you can isolate whether the
short is between the junction block and the joint connector, or by checking
the pink and dark blue wires on the connector, if the short is downstream
towards the SBCM.
Thanks for your suggestions Tom.
I'm assuming the top of the fuseholders are the "feed" side ... could be
that the feed is actually bottom terminal of the fuseholders.
Going to follow up tomorrow.
Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here.
All logos and trade names are the property of their respective owners.