My Mechanic said I need to unplug SGII asap

[bobski]

Originally Posted by brucepick

I considered finding the 12V pin on the OBDII connector and supplying a good solid 12V to it directly.

The horn causing strange behavior isn't all that surprising since it's a pretty high powered electromechanical device (it spits out lots of electrical noise, not just audible). The headlights on the other hand are a pretty stable... They pull a peak of current when you first switch them on, but are a constant load after that.
I would take a good look at your battery and engine ground cables actually. The only power supply wiring shared by the lighting and engine control systems runs from the positive battery terminal to the under-hood fuse box, and from the negative terminal to the body ground point. If there's a bottle-neck that's causing power supply problems, it would most likely be in one of those connections.
Old batteries can sometimes leak acid, which can be picked up via capillary action by the battery terminals and passed on into the battery cables themselves. Once there, it's shielded from the elements and has plenty of time to corrode and dissolve the copper wire. When the cable gets down to only a few strands left to carry power, all kinds of weird gremlins start popping up. The easiest way to detect (and neutralize) an acid leak is to fill a spray bottle with a solution of baking soda and water, then spray it around the battery and cables (so long as the battery's vent covers are in place, the solution shouldn't hurt it). Just like baking soda and vinegar, the solution will fizz up if you hit acid.

[Vwbeamer]

Different make car, but same problem.

I think you need to unplug your mechanic.

Anyway, my car the temp sensor went out and the dash gauge still worked fine. Like others i leave my SG hooked up 24/7.

A. Start working on your own car. this stuff is not hard and there is plenty of info on the net. No one cares more about your car than you do.

2.Go get a temp sensor, and replace it your self. I bet it's easy to replace, mine was.

D. Keep your SGII hooked up. it's fun.It's useful and your mechanic is a tool.

[LUVMY02CREW]

I have left mine hooked up 24/7 for the past couple of years and have never had any problems that I have noticed. It seems like your mechanic has developed an opinion about the Scangauge that is based on faulty info.

[bobski]

Originally Posted by Vwbeamer

I think you need to unplug your mechanic.

+1 to that. The diagnostic code is telling him exactly what's wrong, and the fluctuating readings via the SG seem to confirm it: there's a problem with the coolant temperature sensor, sensor circuit or related wiring. He either doesn't know how, is too lazy or too incompetent to troubleshoot the problem.

1. Look up the location of the coolant temperature sensor on your engine. It will probably be screwed into one of the cylinder heads and have a round 2-wire connector.

2. Make sure there is no obvious physical damage to the sensor and the electrical connector is fully plugged into the sensor. If damaged, replace the sensor. If unplugged or partially unplugged (release tab isn't latched), plug it in properly and go for a test drive.

3. Unplug the sensor and inspect the wiring for damage at and around the connector. This may not be a problem on C-series engines, but the coolant temp sensor wiring takes a beating on D-series engines thanks to being located under the distributor where a bad seal can drip oil down on the wiring, hardening and cracking the insulation which exposes the wire to corrosion from the elements (holy run-on sentence batman). Re-plug the connector if everything looks okay.

4. Check the battery and ground cables as I suggested above if you haven't already. You're looking for corrosion and/or bulges in the insulation near connection points along the cables.

If the above all looks okay, you'll need a multimeter to do some testing. Let me know and I'll walk you through that.

[gascort]

link
It appears that your ECT may be two in one; a sensor and a sender.
Not sure; you will need to check and see how many wires it has, etc.
ECT sender - works the gauge -
ECT sensor - goes to the computer for emissions, fuel, etc.
If you have more than two wires, I bet your sensor does both and sends the signal both ways. Totally unsure though; I'm a Ford guy.

[CigaR007]

You can always plug your SGII in another car to confirm that it works properly.

[bobski]

Originally Posted by gascort

link
It appears that your ECT may be two in one

No. If you look at the list of parts in the link, the one with a black plastic connector is the coolant temperature sensor. The one with a single bullet connector is the gauge sender.