Intermittent Fuel Gauge

[TheAmbit]

Good morning,

I recently replaced the fuel pump on my '06 cruiser. I've put a couple hundred kilometers on since then, and just last night the fuel gauge started to intermittently turn off. The roads are bumpy and full of ice/snow right now, so every 30 seconds or so the gauge will just die and drop to empty (tank is full). The car continues to run so the pump is powered.

For full disclosure when reinstalling it, one of the nubs on the fuel pump body snapped off that holds the electrical connector on. I fixed this with some all weather zip ties. Since the pump is getting power I'm guessing this isn't the issue.

Could it be a ground problem causing the gauge to cut in and out? I have the ground wires that connect to the struts on order (I noticed both were broken when under the car) but they'd likely been broken for a while.

Is there a specific ground location for the fuel pump? Google wasn't helping!

Thanks!

[GtPt05]

Did you check the connectors that are on the passenger side of the tank. You can see them looking straight up from underneath the car. Tucked in beside the cage that holds the emissions stuff.

[TheAmbit]

Originally Posted by GtPt05

Did you check the connectors that are on the passenger side of the tank. You can see them looking straight up from underneath the car. Tucked in beside the cage that holds the emissions stuff.

I did crawl under and jiggle them. Nothing appears frayed or melted and the connections aren't loose (I did have this disconnected when doing the repair). The harness is safely attached to the frame.

I can try disconnecting it and looking inside to see if anything is burnt out; thanks for the suggestion. What is odd to me is that the pump works but the gauge doesn't when all the connections are the same.

[rob302]

a bad ground for the fuel level sender will make the tank read full. if the gauge drops, you have an intermittent connection at that connector or you bought a fuel pump assembly with a bad sender.

play with the connector you ziptied and see what you can do to make sure the metal connections in the connector are clean and tight, and the wires are not damaged from age or from the zipties.

for reference (description and schematics) -bad fuel gauge ground: Embarassing question I have to ask because I made a huge error

[TheAmbit]

Originally Posted by rob302

a bad ground for the fuel level sender will make the tank read full. if the gauge drops, you have an intermittent connection at that connector or you bought a fuel pump assembly with a bad sender.

play with the connector you ziptied and see what you can do to make sure the metal connections in the connector are clean and tight, and the wires are not damaged from age or from the zipties.

for reference (description and schematics) -bad fuel gauge ground: Embarassing question I have to ask because I made a huge error

Thanks so much Rob. Not what I wanted to hear but clears things up I'll have to drive it to get the tank empty before dropping it again (I'm not draining 60L out of it again, that was a nightmare the first time).

[TheAmbit]

I'm getting a code now, P0462 - Fuel level sender voltage wrong.

Going to have to look into that.

[rob302]

Originally Posted by TheAmbit

Thanks so much Rob. Not what I wanted to hear but clears things up I'll have to drive it to get the tank empty before dropping it again (I'm not draining 60L out of it again, that was a nightmare the first time).

you're welcome. check the wires off to the side first though! specifically by the connector. broken copper wire inside a rubber sheath is very difficult to spot. maybe have a helper sit in the car and watch the gauge while you wiggle the wires one by one back there.

[TheAmbit]

Originally Posted by rob302

you're welcome. check the wires off to the side first though! specifically by the connector. broken copper wire inside a rubber sheath is very difficult to spot. maybe have a helper sit in the car and watch the gauge while you wiggle the wires one by one back there.

I pulled apart C304 (the connector passenger side by the emissions box) and tested everything with a volt meter.

It's mapped as such:
1 - Z04 16 BK - Pump relay ground
2 - Z904 20BK/LG - Fuel level ground
3 - N4 20DB - Fuel level sensor
4 - N1 16 DG/WT Pump
5 - K106 20WT/DG (NVLD) - leak detection (don't think this goes to pump)
6 - K107 20OR/YL (NVLD) - leak detection (don't think this goes to pump)


Anyway this is what I'm getting for resistance whether the gauge works or not (whether this is supposed to happen or not I'm unsure, but the car runs):
1&5 - ~8.5 ohm
4&5 - ~8.5 ohm

For 2 & 3, when the gauge isn't working (empty) there's no resistance; just straight current.
When the gauge is working (up near full) it registers 880 ohms.

All other 'combinations' didn't register when set at 200 ohms)

I forgot to mention I replaced the car batter right before this issue happened and I connected the positive first (I read this was bad though I've always been told to disconnect the negative when working on a car) - I wonder if I just damaged the low voltage sensor?

So it's intermittent and the ground cable up near the front passenger fender is secure and looks intact; though since this electrical issue is between the pump and C304; the front ground shouldn't be an issue.

[ptcruisersteve]

P0462 - Fuel Level Sending Unit Low Voltage Conditions

Possible Causes:
1. Faulty fuel level sensor
2. Fuel level sensor harness is open or shorted
3. Fuel level sensor circuit poor electrical connection

Can you reconfirm that the ground wire at the drivers inner fender is making good contact for the fuel sending unit? I am wondering if the ground wire is not making good contact at the fuel level sensor.

[TheAmbit]

Originally Posted by ptcruisersteve

P0462 - Fuel Level Sending Unit Low Voltage Conditions

Possible Causes:
1. Faulty fuel level sensor
2. Fuel level sensor harness is open or shorted
3. Fuel level sensor circuit poor electrical connection

Based on my resistance checking, it's not shorting and it's not a poor connection (I think it would be very odd for the existing wiring to bypass the sensor and run straight current; without affecting anything else in the harness); so if it's just a faulty sensor on the new pump I think I'm just going to ignore it for now. I have AMA in any case