Wiring and warning light questions.

[chevycrew]

Does anyone have access to the pinouts for the transfer case plug?

I need to figure out which wire goes from the t-case to the PCM telling it that its in 4 low.

I have found it in the wiring diagrams. but all I know is its there. Not the wire location.

According to the diagram, its a gry/blk wire #1694, I also need to know if when the TB is in 4 low, is this wire powered, or grounded.

I should have done some playing when the stock t-case was still in the truck!

Thanks!

This is just research for the people wanting to swap in a 231 case. (With my duals I have to go full manual)

[Trail X]

The PCM supplies 12V to the circuit at all times. The TCCM grounds the circuit when in LO range. Otherwise during HI operation the circuit remains ungrounded.

Do you need pinout diagram? It's on the 16 pin connector with 3 unused slots (13 wires). 4WD LO signal is GY/BK wire on pin B5 (lower level, 5th pin).

Hopefully that helps.

EDITED FOR CLARITY

[chevycrew]

Thanks,

Ill ring out the wires to see which wire it is at the transfer case end.

Then someone could use the pcm wire, into the 4wd indicator switch, and out to a ground.

This will allow proper shifting of the transmission when in 4 low.

[chevycrew]

Well that didnt work!

Connector 1 on the TCCM, in position B5, has the input to the PCM for 4low.

Connector 3 on the TCCM, in position A, has a ground.


Connecting the 2 wires together, should have simulated being in 4 low, as far as the PCM in concerned.

[chevycrew]

GOT IT!!!


For those that want to swap in a 231 this is a major plus!

I have all 4 gears in 4 low.



The trick... Remove TCCM entirely, then connect the gry/blk wire in connnector 3 position B5 to the Ground in connector 1 position A.

Put a switch in this circuit and only activate when in 4 low.

[Trail X]

Glad you got it. I took a picture for anyone's future reference, and so we can know what wires we're actually talking about. Ground should actually be B8. If you're using A1 you could be sending bad signals into your system.

[chevycrew]

Im not dissagreeing, but wondering how that C3-A, could send bad signals.

It goes straight to the chassis.

[Trail X]

Sorry I misunderstood which pin you were referencing, I didn't realize you were referencing different plugs. I thought you wer using pin A1 off the same connector as the LO signal, which is a serial data pin. Wasn't reading carefully enough.

So you're connecting B5 from the C1 plug, with A from the C3 plug. Got it.

[chevycrew]

No problem!


Now the next is figuring out my brake warning light.

It looks as only the low fluid level switch, and park brake switch can turn on the light, according to my wiring diagram.


But, fluid is full, e-brake is off.

What else can turn the brake warning light on?

[Diacom]

Isn't it just a switch attached to the E-brake that turns the light on? Perhaps this swich is sticking on you.

[chevycrew]

Ive unhooked and jumped both the low fluid switch, and the e-brake switch.

There has to be more in the circuit, this all started after the build, everything was fine before.

[Diacom]

Grounding issue for one of the switches then?

[chevycrew]

No, the switches have been removed from the equation. Its a simple 2 wire switch. I can leave them both unhooked, or jump wire to wire and I still have a light.

Im thinking its more to due with the computer seeing missing abs, wheel speed sensors, vss. along with t-case, front disco, etc. Im just not seeing in the wiring where there is more in the circuit that can tell the light to go on.




On a positive note, if you unplug the TCCM, the Service 4WD light goes out!

[Trail X]

Looks like both switches are open when things are going ok.

Service manual says to look for shorts to ground on the wiring, then replace the electronic brake controller module. Sorry, I don't see anything else. There is, however, one thing that said you should recalibrate your EBCM for tire size... maybe that's throwing it off somehow.

[The Roadie]

So (per your PM) your tranny still isn't shifting at any RPM when you set the low range? You've got the right pin to ground, and I'm assuming it's grounded for LO mode because that would make the most design sense. Might be that the PCM demands to see the TCCM pass its power-on diagnostics, not go back to sleep, and stay communicating. If the TCCM is there, and fails the power on diagnostics as 2002 TCCMs are renowned to do, then the PCM lights up the Service 4WD lamp. If the TCCM fails to talk at all on the bus, the PCM might just assume it's in a 2WD vehicle, and from that point on, ignores the LO range signal and doesn't allow the tranny to shift as expected because the ground speed never matches what it thinks the gear ratio is.

You might be able to fool the system by getting the VSS to report back a falsely high driveshaft RPM, but that involves designing a PLL circuit. THis may be an intractable problem. I can't figure a workaround yet without leaving the TCCM in and letting it control the actuator and encoder motor as if it's still running the show. For all we know, the PCM is expecting the TCCM to report back front and rear driveshaft RPMs over the data bus. That would be a real deal-killer if you needed sensors on the driveshafts. Crappy GM designers.

A tune might be able to get rid of that restriction, or it might be hidden in a safety-related subroutine the tune software doesn't have access to.

It's stuck in 1st? What's that crawl ratio, about 500 to 1?

And the brake light switch is still on?

[chevycrew]

I had a bad connection in the t-case pcm input. While I was at it, I rewired to make it easier. Following what james said, connector C1, B5 to B8 with a switch. now trans shifts again in 4 low.

[chevycrew]

Now the next is figuring out my brake warning and ABS lights.

It looks as only the low fluid level switch, and park brake switch can turn on the brake warning light, according to my wiring diagram.


But, fluid is full, e-brake is off.

What else can turn the brake warning light on?

Looks like the ABS light is turning on the brake warning light...


Im trying to come up with a solution to fool the ABS into thinking everything is working correctly by modifying the vss output signal into a abs signal for the front wheel speed sensors.

If this works, this will also be able to be used to convert a 4 channel system to a 3 channel for those with older rears in newer trucks.

[janesy86]

Now the next is figuring out my brake warning and ABS lights.

It looks as only the low fluid level switch, and park brake switch can turn on the brake warning light, according to my wiring diagram.


But, fluid is full, e-brake is off.

What else can turn the brake warning light on?

Looks like the ABS light is turning on the brake warning light...


Im trying to come up with a solution to fool the ABS into thinking everything is working correctly by modifying the vss output signal into a abs signal for the front wheel speed sensors.

If this works, this will also be able to be used to convert a 4 channel system to a 3 channel for those with older rears in newer trucks.

This definitely is what happens, been trying to figure it out for a while now. Haven't gone in depth trying to figure it out, but did the usual brake fluid check and e-brake check.

It would be awesome if you figure something out that can correct this problem!

Just to make others clear, mines throwing the lights because I have an 07' with the 4 channel system and used an axle from a 05' with 3 channel...

[DirtyBacon04]

this thread is WAY above my head...

[chevycrew]

Another interesting note. The brake warning light has to go through a computer at some point, If you drive with the warning light on, and the e-brake set, the bulb will start to flash along with the chime (same as lights on, door ajar, key in, etc)

If this solution doesnt work, the next step will be to rewire the brake warning light so it works normally, IE: brake handle and fluid level will turn the light on, and it will turn on with the bulb check. But will not have anything to do with the abs system or the computer. (If possible!!!)