TOD Problem

[RAZ]

Its snowing here, I just took out my VX and I only have power to the back wheels. No TOD check light, but only one of the green bars on the front wheels lights up. With the back wheels spinning. So I stopped and put it in LOW all the green bars lite up still only back wheels spinning. No grinding or strange noises. What broke?
Thanks STEVE

[orion]

WoW, that's a tuffy. if it was one of the speed sensors i think the check light would come on. and if the electric clutch coil failed it would set off the light. my guess is either the clutch pack is not holding(witch should turn the light on), or the TOD computer has a fault. if you haven't yet, down load the shop manual from the downloads section here. there is a good troubleshooting section for TOD problems.

[etlsport]

maybe the tod check light is out?

[mdwyer]

WoW, that's a tuffy. if it was one of the speed sensors i think the check light would come on. and if the electric clutch coil failed it would set off the light. my guess is either the clutch pack is not holding(witch should turn the light on), or the TOD computer has a fault.

Isn't shifting into 4LO a mechanical linkage? That is, doesn't that go around the TOD clutchpack and ignore the speed sensors? I was thinking it was a shaft missing between the engine and the front diff. It would have to be AFTER the speed sensor, though, or else TOD'd would be trying to get those wheels moving...

I nominate the front diff.

Just a wild *** guess, though...

[RAZ]

Is there a fuse for the TOD clutchpack? Maybe I should disconnect the battery to reset the TOD computer? Like I said before no strange noises but right now its just a 2 wheel truck!

STEVE

[RAZ]

The ABS brakes are working do they use the same speed sensors?

[johnnyapollo]

There are two speed sensors - they are basically magnets that "count" the number of RPMs before and after the TOD engages and feed back to the TOD ECU (TOD has a separate ECU that isn't read by typical OBDII readers). When these go out it definitely causes a check TOD light - it blinks and there are no indicators to the front, with the front-wheels disengaged. I went through replacing a set of bad sensors earlier this year.

If one or both sensors are bad, the TOD ECU should throw the check TOD light.
The ABS systems are connected to a separate ECU and do not use the same sensors (those are connected to each wheel and the ABS pump itself).

As suggested, the easiest "fix" is to reset by battery disconnect - this would at least clear everything as a cold reboot to the ECUs. Beyond that, I'm not sure how you can troubleshoot the issue. If you aren't throwing any check lights, the ECUs will probably not contain any data that can be read for diagnosis. Second issue, is that I don't believe the typical code reader can view or display TOD ECU codes (I had to go to the dealer to get the codes - cost me $90 which really sucked). I know for a fact that Autozone and Pep Boys both weren't able to pull the TOD codes, nor could my cheapy reader pull the TOD codes). Since all the electrical systems are double faulted to produce codes when there are problems (as in wiring shorts, ground faults or issues with sensors or ECU), I'm not sure where that leaves you. Hopefully the cold boot will clear things up.

-- John

[MrCrowley]

Heres my 2 cents!

Chances are it is within the transfer case. Why the check light isn't coming on is anyones guess. As a backup, I would try to put it up on jackstands and see what type of drive at all may be going to the front. Especially high and low range. You did mention that the front bars are lit at 85/15 bias. Can you go to a dirt or snow area and floor the gas for 1 second and look for front and rear dig marks cross referenced with what the dash lights are doing? This has given me peace of mind as well when I was questioning if my TOD was working properly. Maybe we are missing something.

Also, I second the advice of resetting your truck via disconnecting the battery. This has eliminated every problem that has ever cropped up on the 3 ECU controlled Isuzus I have owned so far. After that, I would check electrical connections. The no check light remains a mystery for all. Let us know if you find any more interesting differences as this may be the key to finding your gremlin.:luck:

Also, have you checked or changed your TOD fluid lately? What service history has it had?

[deermagnet]

There is a ton of stuff for TOD diagnosis in the manual. It's mostly complex electrical things that they use the Tech 2 Scan Tool to figure out. It says the TOD control unit rarely fails and bad connections are most likely the problem. It does mention the rear wheel spin you have. If the TOD check light is not burned out, but is not blinking, there still could be a code stored. You connect pins 4 and 8 with a wire at the data link and then turn the ignition on to read the codes by the blinking TOD check light.

http://www.drivehq.com/file/df.aspx/publish/mgpa/imgs/tod1.gif
http://www.drivehq.com/file/df.aspx/publish/mgpa/imgs/tod2.gif
http://www.drivehq.com/file/df.aspx/publish/mgpa/imgs/tod3.gif
http://www.drivehq.com/file/df.aspx/publish/mgpa/imgs/tod4.gif

Mark Griffin