4wd Confusion

[Maxcaddy]

Joe, walk me through this one,

Going back to your wiring diagram, the TC clutch is engaged by a 'PWM signal' from the brown wire.

The brown wire is fed from either the TOD or the TCSR.

Now, presumably with the switch in 'Auto', one of them feeds a 'PWM signal' depending on the relative front/rear prop shaft speeds. When switching to 4High, a continous 'PWM signal' will be given by the other one.

Assuming this happens, then by disconnecting say the TOD, I should get either '4Auto', or '4High/Low', as long as the TCSR is working correctly, and if the TCSR has 'blown', I should get nothing as the path is earthed.

Similarly, by reconnecting the TOD and then disconnecting the TCSR, I will get the opposite, either '4Auto' or '4High/Low', as long as the TOD is working correctly. If the TOD has also 'blown' I should again get nothing, as the path is earthed.

Does this make sense, and is it worth doing ?

Thanks

Tony

 

[gijoecam]

Joe, walk me through this one,

Going back to your wiring diagram, the TC clutch is engaged by a 'PWM signal' from the brown wire.

The brown wire is fed from either the TOD or the TCSR.

Correct. However, the only time it's fed from the TCSR is during the shift from from 4low to 4high. Look at the schematic and picture it with the 4low relay engaged. Power flows from the fuse, through the L2H relay contact, through the TCS motor, then grounds through the H2L relay, and goes to earth through the brown wire.

However, during the high to low shift, power flows from the fuse through the H2L relay contact, through the shift motor, back through the L2H contact through the diode I mentioned a few days ago, and to earth through the transfer case clutch coil and the brown wire. (I'll try and draw a picture at home tonight)

Now, presumably with the switch in 'Auto', one of them feeds a 'PWM signal' depending on the relative front/rear prop shaft speeds. When switching to 4High, a continous 'PWM signal' will be given by the other one.

Sort of... let me see if I can explain what I know...

The GEM output to the TOD relay varies from 0-38%. Now, being that the relay is a solid-state unit, it likely amplifies the signal somewhat, but the net output of the relay to the t-case clutch coil is a pulse-width modulated output. That means that the amount of current as well as the voltage will vary over the input range. That essentially changes how much current is sent to the clutch and, therefore, (in theory anyways)how tightly the case locks. (To the best of my knowledge, however, the t-case clutch is essentially on or off... there doesn't appear to be some amount of slippage it allows... but admittedly I've never had one on a bench to play with)

Assuming this happens, then by disconnecting say the TOD, I should get either '4Auto', or '4High/Low', as long as the TCSR is working correctly, and if the TCSR has 'blown', I should get nothing as the path is earthed.

Similarly, by reconnecting the TOD and then disconnecting the TCSR, I will get the opposite, either '4Auto' or '4High/Low', as long as the TOD is working correctly. If the TOD has also 'blown' I should again get nothing, as the path is earthed.

Does this make sense, and is it worth doing ?

I *suspect* that if you disconnect either the TCS relay or the TOD relay, the GEM will detect a fault and disable the system all together. (although again, I've never tried it) Now, if you want to isolate it, here's what I would try: Take the connector from the TCSR, and de-pin the brown wire from the connector. Then see if 4auto works. The system won't know that the connector is missing the 'ground wire' for that circuit unless it tries to shift from 4low back to 4high. That, however, would be the problem: If you happen to shift from 4high to 4low, it will shoft with no problem. However, without that ground path through the t-case clutch coil, the shift relay will not be able to shift the case back into high range. (i.e. it'll be stuck in 4low)

To try it out, you could cut the brown wire where it comes out of the TCS Relay, and install a bullet connector. That would allow you to disconnect the wire for troubleshooting purposes, then just plug it back in and shrink tube or tape it up when it's all said and done. But I suspect it's in that 'leg' of the brown wire where it's grounding-out.

Make sense? (I'll try and draw some pictures tonight when I get home)

-Joe

 

[Maxcaddy]

I *suspect* that if you disconnect either the TCS relay or the TOD relay, the GEM will detect a fault and disable the system all together. (although again, I've never tried it)

-Joe

Yep........I guess that's exactly what will happen

So much for my quick fault finding cure which I had hoped might give me 4Auto, 4High Auto (same thing), and 4Low Auto which for what I use a 4x4 for, would have been more than enough.

No, all done now, have decided to source a TOD & TCSR from breakers and see if that cures it, as well as doing the BWM as its all apart.

Take what you say about de-pinning the (brown) connectors but if fitting 'other' relays cure it, I'd be just messing about.

Please don't spend anymore time on sourcing more detail on this for me, I'm extremely grateful for what you have done so far. I'll report back once the new relays are in.

Ciao

Tony

 

[gijoecam]

Please don't spend anymore time on sourcing more detail on this for me, I'm extremely grateful for what you have done so far. I'll report back once the new relays are in.

Definately keep us (me? is anyone else in here??) posted.... I'm happy to help... if I ever make it over to that side of the pond again, I'll let you buy me a drink and we'll call it even. Until then, I'll just take the good kharma. I'm happy to help when I can.... it's why we're all here.

 

[Maxcaddy]

Ready to go

Hi Joe, I'm back...........

I've now taken out a complete set of relay/modules from an alleged 'good working 98 model' (mine's a 99) comprising of the GEM, TOD, TCSR, and the Auto/4H/4L switch, all for the eqiuivalent of US $48.

I'm tempted to fit all 4 parts so that if it was one part causing another to fail, I won't repeat the problem.

However before I do that, is there any difference between the build standards of the parts, or any other reason why swoppiing the whole lot isn't a good idea ?

Best Regards

Tony

BTW Let me know if you ever cross the pond, I'll treat you to full strength RHD beer.

 

[gijoecam]

Sat down with the connector diagrams for both the 98 and 99... GEM, TOD, and TCS relays...

-The Transfer Case Shift Relay is wired the same for 98 and 99.
-On the GEM, there are several differences... Connector 280 (central timer connector) pin 2 is the CTM diagnostic Connector on the 98, not used on the 99
Connector 282 on the GEM, pin 11 is used as the 4wd low signal output on the 98, not used on the 99

Refresh my memory... the light comes on for both high and low range, but you get nothing at the t-case, right? If the light is coming on, it's not the GEM... I wouldn't bother replacing it. We had it narrowed down to being a short to ground somewhere in the brown wire, right? And IIRC, we were looking at the TCS relay, correct? I'd start there...

Good luck!

 

[Maxcaddy]

OK, I changed the TCSR and nothing seemed to happen, 4H light on, front prop still loose.

Changed the TOD....Whoa..... internal lght tripping on and off, some big relay was making a clicking noise down by the side of the radiator, the panel lights flicking on and off, no 4High light etc, so much so that I took the top connector off the GEMS to quieten things down.

It was then getting dark and the battery has lost a lot of charge as its been stood there for 3 weeks. So I've stopped work and put the battery on charge overnight.

Seems to me that there could be some input (Air Bag sender ?) to the GEMS which is duff/wrong/shorted out, and the result is effecting the 4x4 engagement. The remote locking also stopped working ???

If its not raining in the morning, battle will commence again.

Ciao.

 

[Maxcaddy]

I'm back,

I'm a bit further forward although I've lost 3 days as all that sitting around was too much for the battery (Which I suspect was the original) and it died for good .

So.....with a new battery this is what happens. The engine starts and everything seems OK other than the air bag light now flashes 5 times, there's a short pause then it flashes 2 times, then a short pause, then flashes 5 times again, and so on for about 2 minutes when it then stays lit all the time. (never been an air bag light problem before...ever.)

Right for the main course, switching to 4 high the dash light (4 HIGH) is lit and the front prop engages/disengages on commend. Great so far...

Switching to 4 LOW and moving in/out of 'N' a clunk can be heard so I'm certain that's OK and ...the front prop remains locked. Even better

Therefore, although I haven't tried it out on the road to see if its 'auto' locking, so far so good.

The offending unit appears to be the TOD not the TCSR, and the cause seems to be linked to the Air Bag system (remember the relay/sender unit by the radiator clicking like mad). I do remember that when I bought it (5 years ago) there was a stash of mud stuck in the lower radiator and surrounding areas (air bag impact senders ?) and I suspect it was probably sunk in some swamp nose first for a while.

Although.....to change the TOD I had to take out the passenger (drivers side to you lot) air bag, as the screw is impossible to reach. Therefore I may had started an unrelated air bag issue.

Any advice on what 5 flashes then 2 flashes of the air bag light means would be gratefully recieved. Alternatively is there a fuse or something on the air bag system I can pull to get rid of the light ?

Ciao

 

[gijoecam]

Check the fuse for the air bags... It may have popped.

(LFC = Lamp Fault Code)

Pinpoint Test A: LFC 12/52/DTC B1867 — Lost Battery Feed or Low Battery Feed Voltage

Normal Operation

The air bag diagnostic monitor (14B056) measures the voltage at Pin C232-14, Circuit 937 (R/W). The voltage at Pin C232-14 should be equal to battery voltage. If the voltage at Pin C232-14 drops below 8 volts, the air bag diagnostic monitor will flash a lamp fault code (LFC) 12 on the air bag indicator. If the voltage at Pin C232-14 drops below 5 volts, the air bag diagnostic monitor will store diagnostic trouble code (DTC) B1867 in its memory. Should the loss of battery voltage at Pin C232-14 be intermittent or repaired, the air bag diagnostic monitor will flash an LFC 52 (or higher priority code if one exists) on the next ignition switch cycle.

Possible Causes

WARNING: Do not under any circumstances substitute another fuse value for the power distribution box Mini Fuse 5 (10 A). Any fuse other than 10 A can cause disarming failure and can result in danger to the occupants of the vehicle. Do not attempt to replace the power distribution box Mini Fuse 5 (10 A) unless the battery ground cable has been disconnected and the backup power supply energy has been depleted. To deplete the backup power supply energy, disconnect the battery ground cable and wait one minute. Be sure to disconnect auxiliary batteries and power supplies (if so equipped).

NOTE: If a short to ground exists on any of the air bag module Circuits 607 (LB/O), 614 (GY/O), 615 (GY/W), or 616 (PK/BK), leading to a lamp fault code (LFC) 13 or 53 and a diagnostic trouble code (DTC) B1913; or, similarly, a short to ground exists on any of the air bag sensor circuits 617 (PK/O), 619 (PK/W), 624 (Y/W), or 625 (Y/LG), leading to an LFC 14 or 54 and DTC B1914, the air bag diagnostic monitor will activate an internal solid state switch at Pin C232-13 of the air bag diagnostic monitor. The activation of this switch shorts Circuit 937 (R/W) to ground, causing the power distribution box Mini Fuse 5 (10 A) to open, thus disarming the air bag supplemental restraint system (SRS) and preventing inadvertent air bag deployment.

Lost battery feed voltage at Pin C232-14, Circuit 937 (R/W) can be caused by:

an open in Circuit 937 (R/W).
an open in the power distribution box Mini Fuse 5 (10 A).
an open in the circuits feeding the power distribution box Mini Fuse 5 (10 A).
a short to ground on Circuit 937 (R/W).
Low battery feed voltage at Pin C232-14, Circuit 937 (R/W), can be caused by:

A concern in the charging system causing battery voltage to drop below 8 volts.
After the air bag diagnostic monitor has disarmed the air bag system, it will not be enabled to disarm again until the appropriate condition (DTC B1913 or B1914) has been repaired and cleared by performing the appropriate pinpoint tests.

Start with the simple stuff and we'll go from there... The diagnostic procedure is complicated and lengthy. Hopefully it's just a fuse.

-Joe

 

[Maxcaddy]

Check the fuse for the air bags... It may have popped.

(LFC = Lamp Fault Code)

Should the loss of battery voltage at Pin C232-14 be intermittent or repaired, the air bag diagnostic monitor will flash an LFC 52 (or higher priority code if one exists) on the next ignition switch cycle.


-Joe

Spot on if LFC 52 means 5 then 2 flashes, thats exactly what I have. You've provided an excellant coverage of the Pinpoint tests, but a little deep for me

Spent the afternoon replacing the interior and the seats, as you never know if a disconnected power feed to the seat can trigger the Air Bag light. Other than the radio surround everything is now back in, and if a test drive tommorrw proves the 4x4, the radio etc can go back.

Checked the mini fuse under the bonnet and that was intact, as was fuse 15 (air bag system instrument panel) at the side of the instruments, my handbook also identfies fuse 6 (air bag system, blower relay) but this fuse wasn't present ???

Assuming the simple inasmuch as it was the low battery voltage that triggered LFC 52, taking that its now 'repaired' by fitting the new battery, how can I clear the warning light ?

Many thanks

Tony