"D4" is on all the time.

[Da Flash]

I just bought a '92 LX auto. The first few days it ran fine but, just yesterday I noticed that the D4 light in the dash is on as soon as you turn the car on. Another thing that I noticed was that the car seem to lose about 20-25% of it's power. I shorted the blue connector in the pass footwell and the only code that I'm getting is CEL code 17. From what I've read, that is for the vehicle speed sensor. I do have a pdf copy of the FSM but, I couldn't find the location of the VSS. Some may think that strange but, auto transmissions aren't my specialty. This is the first auto that I've worked on since the 90's!!!!

Any and all comments are appreciated.

[deevergote]

[Da Flash]

Thanks for the picture, Now on to testing/replacing it.

[Da Flash]

Wel after try to test the VSS to no avail, I sourced a couple of used ones from the JY with another TCU. After trying a "non-pigtailed" VSS, I noticed that the D4 went away and the transimission shifted normally for 5-10 mins. After that, the D4 light flashed. I pulled the codes and, this time the D4 was flashing 4 times. I changed the VSS (to a pigtailed version) and the TCU and the car is running normally.............. for now!!

Nice site you guys have here, other than the picture of where the VSS is, I found all the other info in a matter of minutes. I would've found the picture sooner if I had looked through the FAQ's more thoroughly!!!

[deevergote]

Glad you found more info! We've been around since 2003, so there really is a TON of info on here. Pretty much anything you could ever want.

The TCU does tend to fail occasionally as well, so if your replacements still don't fix the problem, I'd pull that TCU and take a look at the solder joints through a magnifying glass (sometimes things are obviously burnt, other times the joints just crack and need to be seen through magnification.) If the new VSS doesn't fix it, the TCU may need to be repaired or replaced. It's unlikely, though, seeing as you only have one code. Usually, a bad TCU throws numerous codes that seemingly make no sense.

[Da Flash]

I kept the original TCU. I tinker with electronics from time to time so, I might try to fix it.

The car is running much better BUT, it's still throw a D4 (flashing 4 times) code when I put it in diagnostic mode. I do have a couple of questions though, Is there a difference between the "pigtailed" VSS and the non-pigtailed?
How exactly would I go about to test it properly??

[deevergote]

That i'm not entirely sure of. There shouldn't be a difference, but any splicing of wires can change the resistance, and can alter the accuracy of the output. It's often a big deal with oxygen sensors, but the VSS isn't something I'd imagine would be affected greatly by that. I'm not certain, though. I've never had to replace my own VSS (though I'm sure the time will come soon enough!)

[Fleetw00d]

The VSS is sort of a rotating switch. There is a 5 volt signal applied to it; output is an alternating 0 - 5 - 0 - 5 ... volts. If your odometers and cruise control work, then the problem is not the VSS. I had a speedometere problem in 2009 with my wagon, (if I remember correctly) I was able to access the left connector (behind the cruise control switch?) for the gage cluster and identify the pin for the VSS signal. With the key on and one front wheel off the ground, I could spin the tire and watch the voltage change with a multimeter. Turned out my problem was with corrosion on the printed circuit board in the cluster.

Just last week, a similar problem to yours occurred on the wagon, D4 on, but the codes were unintelligible. Sent another TCM to my daughter in TX, with some help, she was able to change it out - problem solved.