Grounding transmission harness to chassis ok?

**Ribfeast** · 12-12-2007, 07:26 PM

Hi guys,

I've been intermittently losing 1st and 2nd gear, and the ECU has logged code 62, which is SP1 solenoid failure (or harness failure). Since I have already tried 2 sets of solenoids without the problem going away, I replaced the solenoid plug on the transmission harness.
This didn't fix the problem. I noticed while doing this that the earth wire on the plug seemed to be slightly corroded, I just rubbed the corrosion off with some sandpaper so that the solder would stick.
The actual solenoid wires seemed OK, but I may re-run these too.

After throwing another set of solenoids in the transmission last night, the SP1 solenoid played up (although less, and only once) at lunchtime today.

SO, what I am thinking, is that the earth wire is not up to scratch/corroded, similar to the problem I had with the starter motor solenoid (which I wired a relay to fix).
Is there any problem with me simply wiring the Earth wire of that plug straight to the chassis or battery? When I apply 12V between S1 and E on the plug, the solenoids do not click, making me wonder whether this wire is for something else instead of earth.

So in short, what can I do to make these solenoids get lots of juice, and work properly?

These are the plugs in question:

**CrUZida** · 12-12-2007, 08:57 PM

If the solenoids are like the 1UZ auto's, they earth through the tranny.

The SP2- output is to do with the speed sensor, and separate to the solenoids.

S1 and S2 on the 1UZ are operated by the ecu powering the wire, and the solenoid grounding through the tranny itself.
S3 and S4 on the 1UZ are operated by the ecu earthing the wire (they are given const 12v).

So, in short, no.

I'd check to see if the tranny has a good ground, and if the solenoid wires are continuous to the ecu, and are not earthing out.

Here is the 1UZ one for reference.

**Ribfeast** · 12-12-2007, 09:40 PM

Awesome mate, I'll start working on earthing the tranny better

And may even re-run the S1-3 wires to the ECU with fresh wire.
Would it be worth looking at the grounding of the ECU itself?

I hooked up LEDs (via resistors) to S1, S2, and S3 outputs on the ECU, and they all seem to be activated by 12V, instead of always on. Maybe the V8 tranny is different...

Another interesting thing I noticed, is that the ECU is keeping S1 active when in Park and reverse, on on some occasions when I am doing over 100kph (in 4th gear). This would mean I am only in first gear, which obviously isn't true as it is revving low. Bizarre...

**thechuckster** · 12-12-2007, 10:15 PM

fwiw: you used to find an earth strap (on older toyotas - not sure about new stuff) from one of the trans mount bolts to the cross member - much like you find a sizable earth strap from back of head to firewall on most RWDs.

You still need a decent-sized strap from block to chassis.

**brett_celicacoupe** · 12-12-2007, 10:45 PM

the ecu sees symptoms that indicate S1 failure but the problem may be in the valve body.
id check for power as close to the solenoid as possible, maybe even measure current. you can also test the solenoid by powering it while blowing in it with your mouth.

if the solenoid is good and its powering properly then id look deeper

**CrUZida** · 12-12-2007, 11:12 PM

Measure the resistance between the S1, S2 and S3 pins on the gbox and the body of the box.

They *should* be fairly simliar readings to what I have listed.
Then measure from the box to a point on the chassis.

Although, if only S1 doesn't work I'd be looking at either the ecu itself, or the wire from the ecu to the solenoid.

This is assume the solenoid itself is fine, and as Brett suggested hydraulically the gbox is operating.

http://www.autoshop101.com/forms/h16.pdf
Have a good read

**Ribfeast** · 12-12-2007, 11:38 PM

It's a brand new rebuilt transmission, and I've tried 2 sets of good solenoids straight from the transmission builder. The old transmission had the same symptoms also, so it's gotta be electrical

You might be onto something there though, since it is always S1 that fails, it might simply be the wire to that solenoid, or possibly the ECU (hope not!).
S1 and S2 from my old auto are in a mate's car and are performing flawlessly...so that furthers the suspicion that my old auto was fine and it was a bloody electrical fault all this time

If I get some time this weekend I'll run a fresh wire from the ECU to that solenoid and see if it improves