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Not getting Fuel Sender voltage http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=91727 |
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Author: | Fyodor [ Thu Oct 29, 2020 7:01 pm ] |
Post subject: | Not getting Fuel Sender voltage |
OK, CRD Wizards, I have a tough one. A couple of years ago I put a Cummins lift pump in my rig and ponied up for one of those pre-made wiring harnesses sold by a vendor here on Lost Jeeps(well worth it!). Everything went fine except that I lost my fuel gauge. It sits empty. No trouble code. Did the dash gauge check and it says the gauge is fine. I did a little bit of poking around before everything went back together and couldn't find anything except no voltage on either sender wire. I have ran it fine for the last couple of years using the trip meter for fill ups, but finally decided to go back in and figure this out. I lowered the tank and unplugged the harness, still no voltage. I even plugged it into the old sender and moved the resistor position around, still no signal at the gauge, and sorta confirms that I don't need to pull the pump out of the tank. Then I unplugged the new harness at the point under the rear seat and tested for voltage on the factory harness. Nothing. Everything else works fine, power to the pump etc. I even started the rig and unplugged the harness and tested for sender voltage on the factory side, nada. FWIW continuity is fine on the new harness to the pump. It's my understanding from reading other related threads that sender voltage comes straight from the PCM to the sender which then returns and the resistance is calculated in the PCM which decides what level the gauge shows. My question is: Are there any fuses or relays in that circuit? I'm not aware of anything. If not, does this mean I need to take the rig into a dealer and have them reset/reflash the PCM? I can not figure this one out!!! |
Author: | fool4wheelin [ Fri Oct 30, 2020 12:55 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
I recently installed a lift pump in my CRD, except I modified my existing harness instead of purchasing the pre-fab harness. I like your idea of trying the old sending unit, do you also have your old harness you could try? I don't know what kind of voltage you should be seeing at the factory connector under the seat, all the ECU is doing is measuring resistance, so I don't think you'll necessarily see 12V. The connector at the sending unit has 4 pins, 2 for the lift pump and 2 for the level sensor. So to confirm: - Your fuel gauge has not worked since you put the lift pump in? - Your lift pump is working fine? |
Author: | p14175 [ Fri Oct 30, 2020 6:50 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Did you swap out the fuel level floats? |
Author: | Fyodor [ Fri Oct 30, 2020 9:43 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
LOL, yes I swapped the floats. Correct, the 2 blue wires are for the sender and there is zero voltage going through either one, key on, running or key off(obv). Power is fine to the pump. I have continuity through all 4 wires on the new harness so there's no need to swap out harnesses. Another bit I didn't share, when I originally drained the fuel tank I used an electric pump and siphoned everything out of the tank through the filler hole with the key off. That means when the rig was shut off the tank had fuel in it. For some reason after I drained the tank I turned the key to the on position, and that's when the gauge dropped to zero and the low fuel light came on and has stayed that way. I was reading through the shop manual that since the PCM and controls the gauge position, troubleshooting gauge problems needs to be done with diagnostic equipment, so I am leaning towards just taking it to a shop. I've worked on vehicles for over 30 years(professionally for 20 of them) and I HATE it when I get to this point- and it's getting more and more frequent! |
Author: | Billybob [ Sat Oct 31, 2020 2:32 am ] |
Post subject: | Re: Not getting Fuel Sender voltage |
You can download the Jeep KJ Service manuals here....Section 8W has the wiring diagrams. http://www.colorado4wheel.com/manuals/Jeep/KJ/ |
Author: | WWDiesel [ Sat Oct 31, 2020 12:11 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Fyodor wrote: LOL, yes I swapped the floats. Correct, the 2 blue wires are for the sender and there is zero voltage going through either one, key on, running or key off(obv). Power is fine to the pump. I have continuity through all 4 wires on the new harness so there's no need to swap out harnesses. Another bit I didn't share, when I originally drained the fuel tank I used an electric pump and siphoned everything out of the tank through the filler hole with the key off. That means when the rig was shut off the tank had fuel in it. For some reason after I drained the tank I turned the key to the on position, and that's when the gauge dropped to zero and the low fuel light came on and has stayed that way. I was reading through the shop manual that since the PCM and controls the gauge position, troubleshooting gauge problems needs to be done with diagnostic equipment, so I am leaning towards just taking it to a shop. I've worked on vehicles for over 30 years(professionally for 20 of them) and I HATE it when I get to this point- and it's getting more and more frequent! What year model is your Jeep? You don't have a signature or say. Adding vehicle information helps others when trying to help diagnose problems and provide help. You can add your vehicle information by clicking on "User Control Panel" in the upper right hand corner, then click on "Profile", then "Edit Signature". ![]() I don't believe draining the tank had anything to do with your problem. ![]() According to the FSM, the Fuel Level signal on an 05 model goes through the Front Module and then to the Body Module which controls the gauge in the Instrument Cluster. For an 06 model, it is wired to the Body Module which controls the gauge in the Instrument Cluster. This is what they list in the FSM on how it functions: FSM wrote: FUEL LEVEL SENDING UNIT / SENSOR DESCRIPTION The fuel gauge sending unit (fuel level sensor) is attached to the side of the lower fuel tank module. The sending unit consists of a float, an arm, and a variable resistor track (card). OPERATION For Fuel Gauge Operation: A constant current source of approximately 32 milliamps is supplied to the resistor track on the fuel gauge sending unit. This is fed directly from the Engine Control Module (ECM). [NOTE: For diagnostic purposes, this 12V power source can only be verified with the circuit opened (fuel tank module electrical connector unplugged). With the connectors plugged, output voltages will vary from about 0.6 volts at FULL, to about 8.6 volts at EMPTY (about 8.6 volts at EMPTY for Jeep models.] The resistor track is used to vary the voltage (resistance) depending on fuel tank float level. As fuel level increases, the float and arm move up, which decreases voltage. As fuel level decreases, the float and arm move down, which increases voltage. The varied voltage signal is returned back to the ECM through the sensor return circuit. Both of the electrical circuits between the fuel gauge sending unit and the ECM are hard-wired (not multi-plexed). After the voltage signal is sent from the resistor track, and back to the ECM, the ECM will interpret the resistance (voltage) data and send a message across the multi-plex bus circuits to the instrument panel cluster. Here it is translated into the appropriate fuel gauge level reading. Refer to Instrument Panel for additional information. DIAGNOSIS AND TESTING - FUEL LEVEL SENDING UNIT The fuel level sending unit contains a variable resistor (track). As the float moves up or down, electrical resistance will change. Refer to Instrument Panel and Gauges for Fuel Gauge testing. To test the gauge sending unit only, it must be removed from vehicle. The unit is a separate part of the lower fuel tank module section. Refer to Fuel Tank Module Removal/Installation for procedures (remove only the upper section of the fuel pump module). Measure the resistance across the sending unit terminals. With float in up position, resistance should be 20 ohms (+/- 5%). With float in down position, resistance should be 220 ohms (+/- 5%). ![]() |
Author: | Fyodor [ Sat Oct 31, 2020 12:43 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
It's a 2006 I saw that info posted on another thread here and that's what had me hunting for voltage in one of the sender leads. There is none in either lead in any key position |
Author: | Billybob [ Sat Oct 31, 2020 2:47 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Fyodor wrote: It's a 2006 I saw that info posted on another thread here and that's what had me hunting for voltage in one of the sender leads. There is none in either lead in any key position Download the 2006 Jeep KJ manuals from the link I posted above and go to section 8W for the wiring diagram....I will have a look through it now! OK page 8W-30-21 of the 2006 KJ Service Manual shows the "Module Fuel Pump" which has the icon of a "motor" ![]() This BR/DG wire also goes off to Page 8W-45-9 via splice S240 where the ground is supposed to be and this page shows two wires on the "Module Fuel Pump" as before and the wire is shown to go to page 8W-45-12 through C120 where it probably picks up Ground. Then there is the Brown/Dark Blue wire ie. Brown with a Dark Blue Stripe...coming from the "Module Fuel Pump" also going through those connectors C307 and C201 and then to BCM C2 Pin #17..may be a break in this wiring! ![]() |
Author: | Fyodor [ Sat Oct 31, 2020 3:34 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Thanks! |
Author: | Billybob [ Sun Nov 01, 2020 7:01 am ] |
Post subject: | Re: Not getting Fuel Sender voltage |
This is very neat information from WWdiesel^^^^ ![]() I usually check wiring by taping a small needle or pin to one of the meter leads. I then piece the insulation with the pin/needle to make my measurements and then seal the pieced insulation with glue or by melting the plastic when finished. ![]() Make sure you do not touch the meter leads with bare hands while doing this. ![]() |
Author: | WWDiesel [ Sun Nov 01, 2020 9:53 am ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Billybob wrote: This is very neat information from WWdiesel^^^^ ![]() I usually check wiring by taping a small needle or pin to one of the meter leads. I then piece the insulation with the pin/needle to make my measurements and then seal the pieced insulation with glue or by melting the plastic when finished. ![]() Make sure you do not touch the meter leads with bare hands while doing this. ![]() Billy, Instead of melting plastic or using glue, get yourself some "Liquid Tape". I use it anytime I pierce a wire for testing purposes or need to simply fix some insulation damage on a wire. Good stuff! ![]() There are several brands on the market. ![]() ![]() |
Author: | Billybob [ Sun Nov 01, 2020 12:31 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Thanks but this is Africa...we do not have the large range of goods available here that you guys get in the USA/Canada/Europe! ![]() Besides I hope that I do not have to do so much more fault finding...especially on my Jeep...that I would need a large tin of stuff like that! ![]() Maybe just an eye-drop dispenser full will tide me over! ![]() |
Author: | Fyodor [ Sun Nov 01, 2020 3:35 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Well for the first time in 2 years I have a fuel gauge again! Looks like the vendor I purchased the wiring harness from had wired it for a gas vehicle. When I moved the pins to the diesel pinouts the gauge woke right up! I have moved twice in the last couple of years and absolutely can not find my old sender harness to compare. Oh well. call this a success story and I have you guys to thank! cheers! ![]() ![]() ![]() ![]() ![]() |
Author: | WWDiesel [ Sun Nov 01, 2020 4:46 pm ] |
Post subject: | Re: Not getting Fuel Sender voltage |
Yea!!!! Happy for you and love happy simple endings.... ![]() ![]() ![]() ![]() Wiring diagrams win again! |
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