Fuel Gauge Woes

[Tectron]

2004 Venture LT

The newest problem I am having that I haven't resolved is that the fuel gauge is showing empty, low fuel light on, range on trip computer says (E). I repaired the wiring harness's on the left and right front due to ac leakage, and I also repaired the pass through behind the drivers seat. This seemed to resolve many of the problems I was having. The thing I noticed is that before I repaired the pass through connector the gauge would work intermittently but now its totally dead. I find it unlikely that the sender and the connector would go out at the same time. Does anyone have a wiring diagram of that connector, or at least which color the wires are for the sending unit and the resistance values I should get?

Thanks

[Airjer_]

You'll be looking at a purple wire and a smaller black wire.

[Tectron]

Cool, do you happen to know the range of resistance from full to to empty? It seems like I read on here 150 ohms is equal to a half tank, but I cant seem to find the post.

[Tectron]

Ok, I pulled the plug(fuel tank side) and checked the resistance between the purple and black wire, and had my son bounce the van and the reading fluctuated from 86 ohms to 96 ohms, so it seems the sending unit is functioning properly. But when I connected a jumper wire to the corresponding pins on the pass through connector there is no change in the fuel gauge reading. Is there still something between the pass through and the gauge that I could check?

[lesterl]

Did you cut and solder the wires (eliminating the pass thru)? If you didnt check the PINS in the connector for corrosion. How did you repair the connector?

[old_master]

When you unplug the harness to the sending unit, the gauge should read full. If it didn't move, the purple wire is a shorted to ground between the connector and the PCM. The purple wire runs from the sender to the PCM. Fuel level data is sent to the instrument cluster through class II communication.

Obviously there is a connection at the PCM and at the sender, but there are also 3 connections between them. You can narrow down your search by unplugging connectors until the gauge reads full. If there's no change, there may be a problem between the PCM and the instrument cluster, or a faulty PCM, cluster, or wiring between them. As Airjer mentioned, the smaller black wire supplies reference voltage to the sender. It should be around 5 VDC, (at the sender) with the sender unplugged, and the key in the RUN position. It goes through the same connectors as the purple wire all the way to the ECM.

[Tectron]

Awesome, this should give me info to trace it down I hope.

I didn't eliminate the connectors but disasembled them and cleaned all of the pins with sandpaper and cleaner, on the plugs that plug in from underneath i soaked them in strong iron out solution and cleaner and compressed air, (they looked like new) that's why I was surprised when I still had problems.

I'll post an update when I trace it down.

[lesterl]

Lettuce know.... :-)

[Tectron]

I checked the black/white wire to ground and got 5.3 vdc, so all seems well there, purple wire to ground is .8 ohms, so there certainly seems to be a short someplace. It will be a week or so before I can re-dismantle the harness, But I'm thinking since it worked intermittently before I worked on the plug, that the short is probably somewhere near the drivers side door post area.

[old_master]

Disconnect the ECM connector, start unplugging connectors and check resistance on the purple wire to ground until the ohm meter shows an open circuit. This will narrow the possibilities and help determine where the short to ground is.

[Tectron]

I finally got some time to disconnect the harness from the computer and wallah the fuel gauge pegged over to full, so I'm certain the short is in the 3-4 foot section of harness in between the two points.

As a side note, does anyone have any experience with the service manual Cd's that are on Ebay for about $15? I would like to get the wiring diagrams so I can see if my abs/traction control problems are linked to the crappy harness, Ive had so many problems due to it that I'm not convinced that my wheel sensors are the problem.

I think once I can get all of these things fixed this van should easily give me 250k + miles.

[pbavion]

My shop had to replace the instument cluster after damaging a trace while changing out the heater core. The fuel guage was setting on empty with 19 gal on board. They reset the fuel guage to full (also removed the low level light I suspect since it does not test) and now the guage only read full. I pulled the plug under the DP floor board and the gauge goes way past the full setting. The sender is reading about 47 ohm at apx 10 gals left on board. Where do I go next to get the guage to work correctly?

[pbavion]

second question, when I pull the connector under the passenger floor and the guage goes all the way arround, can I reset the dial on the fuel gauge to full at that point before connect the floor plug back up?

[old_master]

Originally Posted by pbavion

....They reset the fuel guage to full...

There are no procedures for "resetting" the dash gauge. If they manually moved the needle on the gauge, they probably destroyed the gauge and it will need replacement. If they bent the float arm on the sending unit, it can be recalibrated but requires draining the tank using the fuel pump, removal of the fuel tank and pump module, adjust the float arm so the dash gauge indicates empty.

Originally Posted by pbavion

....and now the guage only read full.

Confirmation that they screwed up.

Originally Posted by pbavion

.... also removed the low level light I suspect since it does not test.

They did this to cover up their screw up.

Originally Posted by pbavion

....I pulled the plug under the DP floor board and the gauge goes way past the full setting.

Normal operation. If there is an open circuit in the fuel level indicating system the gauge will indicate past "full". If there is a short to ground, it will indicate past "empty". Aparently they left all of the connectors intact.

[pbavion]

Thanks and I agree with your assesment after ringing out more of the wiring. The shop did agree to replace the cluster at no cost to myself.