My Diag: Seatbelt Control Timer Module - 0.5A parasitic draw
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From: Atlanta, GA
My Diag: Seatbelt Control Timer Module - 0.5A parasitic draw
1999 Club Cab. Affects Club Cab and 1998 but think they got rid of the module around 2000 or 2001. Single cab has different seat belt retractors so no SCTM.
If you've got the black plastic module under the center console attached to a steel bracket, this affects you. Otherwise... not.
tldr; if you track your 0.5A parasitic draw from IOD fuse then eliminate the draw by unplugging the SCTM, the SCTM may not be going to sleep is there's still a slight resistance on either Pin 2 or Pin 3 with doors closed.
what to test before replacing the SCTM: check for resistance at connector pin 2 and 3 with both ground and +12V. If you detect any resistance (door closed) then this applies to you because this is miniscule signal is causing the SCTM to not go to sleep.
So I've had the 0.5A parasitic draw. Coming from IOD fuse circuit. Traced it down to the Seatbelt Control Timer Module keeping the seat belt solenoids energized with engine off. Seatbelts will never lock with engine off and truck level. It's supposed to sleep after 30 minutes then lock the belts by de-energizing the solenoid.
Probably familiar to some of you. And the unsafe hacks to fix it.
I had the issue and I diagnosed it and found WHY the module was not sleeping after 30 minutes.
First, bench test the SCTM.
I pulled the module out and powered it by grounding pins 6 and 13. Applied +12V to pin 5 (B+). Then I attached a small bulb to ground and pin 7 (left seatbelt solenoid control)
The bulb stayed lit for 30 minutes then turned off. This is how long the SCTM energizes the solenoids so you can pull the seatbelt out after you turn off the engine.
Same right seatbelt solenoid control, bulb lit for 30 minutes then turned off.
So without any other inputs to the SCTM, the module works.
The inputs I looked at were Pin 2 (left door ajar switch sense) and Pin 3 (right door ajar switch sense) on the connector harness
Pin 3 was OK. Voltmeter between pin 3 and +12V was 0 with door closed. 12V with passenger door open. With door closed, showed no resistance between Pin 3 and ground nor +12v
Pin 2 was not OK. With voltmeter between Pin 2 and +12V showed 12v with driver door open and closed. With door closed 90 ohm resistance to ground. Not enough to operate the dome light but enough to cause SCTM to never sleep.
Removed left door jamb switch and tested it. Tested OK.
With LD jamb switch removed, I was still reading 90 ohms at pin 2.
The only valid states of Pin 2 is ground signal with left door open. When door is closed, it should show open circuit.
Cut wire 2 on the wiring harness to eliminate left door jamb switch trigger to the SCTM.
Plugged everything back up. Checked seat belt... I could pull the seat belt in and out of the retractor. So the SCTM was energizing the seat belt solenoid.
Rolled down window and went in the house for 30 minutes.
Came back out and seat belts were LOCKED as expected.
Until I track down WHY there is 90 ohms on Pin 2 when there should be no continuity between ground and +12V... cutting wire 2 on the harness is the safest fix without losing any functions than unsleeping the SCTM by opening the driver door. Turning ignition on, opening passenger door, will still unsleep the SCTM.
Looking at wiring diagrams, it looks like only the left door jamb sense goes to the CTM. Possibly the CTM is leaking some electrons to the SCTM via wire 2. I'll probably (one day) wire a diode at the wire I cut (or wire connecting LD sense to CTM) that should halt the miniscule current flowing to SCTM pin 2.
In my case, the SCTM was not faulty, so even if I had ordered another one off ebay, I would still have the same issue.
Just putting this diag here for future reference.
The only inconvenience is when the SCTM is asleep, opening left door will not wake the SCTM to allow seat belts to pull out and buckle. Have to trigger seatbelt release 30 minute timer by other means: open passenger door or ignition on then the SCTM will wake for 30 minutes and release seatbelts.
If you've got the black plastic module under the center console attached to a steel bracket, this affects you. Otherwise... not.
tldr; if you track your 0.5A parasitic draw from IOD fuse then eliminate the draw by unplugging the SCTM, the SCTM may not be going to sleep is there's still a slight resistance on either Pin 2 or Pin 3 with doors closed.
what to test before replacing the SCTM: check for resistance at connector pin 2 and 3 with both ground and +12V. If you detect any resistance (door closed) then this applies to you because this is miniscule signal is causing the SCTM to not go to sleep.
So I've had the 0.5A parasitic draw. Coming from IOD fuse circuit. Traced it down to the Seatbelt Control Timer Module keeping the seat belt solenoids energized with engine off. Seatbelts will never lock with engine off and truck level. It's supposed to sleep after 30 minutes then lock the belts by de-energizing the solenoid.
Probably familiar to some of you. And the unsafe hacks to fix it.
I had the issue and I diagnosed it and found WHY the module was not sleeping after 30 minutes.
First, bench test the SCTM.
I pulled the module out and powered it by grounding pins 6 and 13. Applied +12V to pin 5 (B+). Then I attached a small bulb to ground and pin 7 (left seatbelt solenoid control)
The bulb stayed lit for 30 minutes then turned off. This is how long the SCTM energizes the solenoids so you can pull the seatbelt out after you turn off the engine.
Same right seatbelt solenoid control, bulb lit for 30 minutes then turned off.
So without any other inputs to the SCTM, the module works.
The inputs I looked at were Pin 2 (left door ajar switch sense) and Pin 3 (right door ajar switch sense) on the connector harness
Pin 3 was OK. Voltmeter between pin 3 and +12V was 0 with door closed. 12V with passenger door open. With door closed, showed no resistance between Pin 3 and ground nor +12v
Pin 2 was not OK. With voltmeter between Pin 2 and +12V showed 12v with driver door open and closed. With door closed 90 ohm resistance to ground. Not enough to operate the dome light but enough to cause SCTM to never sleep.
Removed left door jamb switch and tested it. Tested OK.
With LD jamb switch removed, I was still reading 90 ohms at pin 2.
The only valid states of Pin 2 is ground signal with left door open. When door is closed, it should show open circuit.
Cut wire 2 on the wiring harness to eliminate left door jamb switch trigger to the SCTM.
Plugged everything back up. Checked seat belt... I could pull the seat belt in and out of the retractor. So the SCTM was energizing the seat belt solenoid.
Rolled down window and went in the house for 30 minutes.
Came back out and seat belts were LOCKED as expected.
Until I track down WHY there is 90 ohms on Pin 2 when there should be no continuity between ground and +12V... cutting wire 2 on the harness is the safest fix without losing any functions than unsleeping the SCTM by opening the driver door. Turning ignition on, opening passenger door, will still unsleep the SCTM.
Looking at wiring diagrams, it looks like only the left door jamb sense goes to the CTM. Possibly the CTM is leaking some electrons to the SCTM via wire 2. I'll probably (one day) wire a diode at the wire I cut (or wire connecting LD sense to CTM) that should halt the miniscule current flowing to SCTM pin 2.
In my case, the SCTM was not faulty, so even if I had ordered another one off ebay, I would still have the same issue.
Just putting this diag here for future reference.
The only inconvenience is when the SCTM is asleep, opening left door will not wake the SCTM to allow seat belts to pull out and buckle. Have to trigger seatbelt release 30 minute timer by other means: open passenger door or ignition on then the SCTM will wake for 30 minutes and release seatbelts.
