GU1 Sub Tank Switch

Hello,

I have been having issues with the dreaded GU sub tank light on dash issue. It has happened before and fixed itself after a couple of weeks ignoring it. This time it seems to not want to come right. I have tried disconnecting the battery and no luck.

I started to read the manual and have found the relevant section but, I cannot seem to get the diagnoses mode to activate.

"SELF-DIAGNOSIS PROCEDURE
After turning the ignition switch ON, turn the sub fuel tank switch ON and OFF more than 5 times. Make sure the indicator lamp directly above the sub fuel tank switch flashes every 2 seconds. If the indicator lamp does not flash, repeat the check procedures. (The self-diagnosis system will then start.)"

I cannot get it to flash and do not know what it means by "repeat the check procedures". I have done some more reading and I am considering buying a new sub tank switch, though at nearly $90 I though I should ask the experts first.

Once again, thanks in advance for your time,

Cam

Sorry, 99 GU1 Wagon TD42T manual

By "repeat the check procedure" they mean repeat After turning the ignition switch ON, turn the sub fuel tank switch ON and OFF more than 5 times.

It doesn't always work first attempt and IIRC you have to turn it on and off 5 times in less than 10 seconds or somesuch.

The only time I used it on my '99 Ute about 12 months ago I got it to work on my third attempt, read the code, fixed the fault and it has been fine ever since... but I wondered at the time how it would work if the switch was faulty.

Does the switch lamp illuminate at all when you press it normally?
Most faults the lamp will come on then go out after 5 seconds or so

One other thing, the sub tank circuit is very prone to faults about the earth... have you tried an extra earth from the tank to the chassis ?

Do both the sub tank and main fuel gauges work correctly?

The sub tank switch is just a momentary on switch with a light so it's easy to test.

The switch does not light up at any stage, I pulled the connector out from the switch and made sure everything looked right. Not having a light at all led me on the faulty switch path, I was going to try to run the multimeter over the switch today but was scared off by a coil looking thing on the circuit diagram for the switch and didn't want to accidentally fry anything. Is there a way to test all the funtion of the switch this way?

As far as the earth goes, I haven't been under to look at the tanks yet, is there an existing place to just add another earth or do I just follow the original earth? I'm assuming, form your post, that the tanks have earth leads of their own to the chassis?

Sorry Yendor, you answered a question I was typing as you posted, I will go pull the switch now, and have a look at the terminals I have to test. The diagram was a little confusing, though it looks like it may be pretty simple to somebody who knows what they are looking at

The points on the back of the switch as I look at them are :
- -
----

If that makes any sense, I have 2 contacts on the top row one on the left and one on the right, with 4 contacts across the bottom row

Don't worry about pins 5 and 6 there for the switch to light up when the dash lights are tuned on.

Pin 3 should have power with the ignition switch is on. The coil looking thing is just a drawing for a bulb.

In you earth pin 4 the light in the switch should come on. If your using a multimeter pin 4 will have around 12 volts until the bulb lights up. Then it should have around 0 volts.

Pins 1 and 2 are the switch. Pin 2 is connected to earth.

You can either check the switch contacts with an ohmmeter. With the switch disconnected you should have an open circuit between pins 1 &2 until you push the switch in. or

With switch connected and voltmeter connected to pin 1 there should be a reading of somewhere between 5 to 12 volts. When the switch is pushed in it should drop down to 0 volts.

M48 at the bottom of the picture shows the pin configuration in the plug.

The top two (terminal 1 and terminal 2) are the switch contacts, open cct normally, short circuit if switch held depressed.

The bottom 4 pins are for the globes
Terminal 3 and 4 are the sub tank light,
5 and 6 are for the dash illumination so don't matter for operation

The plug terminal numbering is
1 - - 2
3 4 6 5

edit...DOH must learn to type faster

Ok so...

Terminals 1 and 2 act as they are supposed to.

#1 is showing around 5.04v until the button is depressed, then down to zero.

Pin #3 has around 500mv.

Pin #4 is where my issues start, I do not have any voltage and grounding it does not illuminate the light on the switch.

I have just bought a new multimeter from Jaycar and it has some strange induction thing that i don't understand so my 500mv may have been a false reading of zero. The car has gone to the movies now with the missus as I am about to leave for night shift, so re-testing will have to be done tomorrow.

Could a faulty light lead to a zero reading? Could this lead to the diagnoses mode not activating correctly?

Is the "Sub Tank" fault light on the dash cluster illuminated?
... and just checking that you do know the system will not transfer unless certain conditions are met IE Main Tank less than 3/4 full etc

Anyway, put the multimeter on Ohms and see if you have continuity on the switch between pin 3 and 4?

If you do (and the "Sub Tank" fault light is on)... the globe is OK and there is a fault in the Sub Tank system which the Computer is seeing during self test.