Plz help forum sages RE: fuel gauge. - JeepForum.com
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post #1 of 36 Old 03-22-2020, 12:11 PM Thread Starter
Blue2kWJ
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Plz help forum sages RE: fuel gauge.

So I have a new to me WJ that I am working on. I get the P0462 code. Getting 197 Ohms at fuel pump connector and same value at Pin 4 C1, Pin 26 C3 after fixing a bad ground. Gauge is still reading nothing with fuel low warning indicator. I do the gauges check with the key on, hold distance reset button depressed to reset/check cluster function. I get a check gauges red light msg on cluster. Overhead console doesn't recognize fuel consumption. Everything seems to work ok.
Where do I go next?

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post #2 of 36 Old 03-22-2020, 08:26 PM
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Quote:
Originally Posted by Blue2kWJ View Post
So I have a new to me WJ that I am working on. I get the P0462 code. Getting 197 Ohms at fuel pump connector and same value at Pin 4 C1, Pin 26 C3 after fixing a bad ground. Gauge is still reading nothing with fuel low warning indicator. I do the gauges check with the key on, hold distance reset button depressed to reset/check cluster function. I get a check gauges red light msg on cluster. Overhead console doesn't recognize fuel consumption. Everything seems to work ok.
Where do I go next?
Getting 197 Ohms of resistance at the fuel pump connector?? That sounds like a HUGE amount of resistance. Are you testing the fuel pump connector from the fuel pump or the harness connector?

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post #3 of 36 Old 03-22-2020, 11:34 PM
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I did not see you post signal voltage.

Anyway check attachment does it help?
Attached Files
File Type: pdf wj p0462.pdf (57.5 KB, 12 views)

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post #4 of 36 Old 03-23-2020, 07:33 AM Thread Starter
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Originally Posted by Mattyjm View Post
Getting 197 Ohms of resistance at the fuel pump connector?? That sounds like a HUGE amount of resistance. Are you testing the fuel pump connector from the fuel pump or the harness connector?
I am getting 197 at the fuel sending unit connector -> fuel tank and 197.8 at Pin 4 on C1, Pin 26 C3. I believe that should be in spec for the Bosch unit(20 Ohm Full, 270 Ohm empty). I put some gas in to ensure that it wasn't actually empty.
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post #5 of 36 Old 03-23-2020, 07:39 AM Thread Starter
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Originally Posted by jtec View Post
I did not see you post signal voltage.

Anyway check attachment does it help?
Yes, thank you!!

I am getting 10.7 volts(on my multimeter) key on/Engine off when connected to the vehicle side of the fuel pump connector at the rear wheel. Hmm...
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post #6 of 36 Old 03-23-2020, 07:47 AM Thread Starter
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Originally Posted by Mattyjm View Post
Getting 197 Ohms of resistance at the fuel pump connector??
Yep and you just gave me a great idea. I am going to add a bit of fuel to see if than value shrinks a bit. That should prove that the ending unit is functioning or not.
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post #7 of 36 Old 03-29-2020, 09:58 AM Thread Starter
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Update:
1. So I added some fuel to the tank. The resistance at the fuel pump connector shows a decrease in the resistance to 145 Ohms which is what it should be doing. This value is reflected in the wiring at C1,pin4 and C3,pin 26.
2. Voltage at Fuel pump connector/vehicle side with key on gives a value of 10.5 volts, same as what is showing at PCM.

So with key on fuel gauge stays on empty with low fuel warning light lit. Starts, runs fine fuel gauge doesn't move, EVIC reading 0.1 miles/gal

Next step is giggle wires at PCM with key on to see if maybe the actual connectors are flaky/corroded or some such thing.
Maybe the PCM is cooked? But the fuel gauge is literally the only thing not working.
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post #8 of 36 Old 03-29-2020, 10:11 AM Thread Starter
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Edit to add, still getting a P0462 code as well 0.0 DTE.
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post #9 of 36 Old 03-29-2020, 01:54 PM
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Originally Posted by Blue2kWJ View Post
Edit to add, still getting a P0462 code as well 0.0 DTE.
Have you tested the continuity of the entire circuit? Including the instrument cluster.
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post #10 of 36 Old 03-29-2020, 04:36 PM Thread Starter
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Have you tested the continuity of the entire circuit? Including the instrument cluster.
The instrument cluster is just displaying output from the PCM and everything else in the cluster is working correctly. Also, the EVIC is showing that it doesn't see the fuel level so that is having me believe that the cluster is not getting the fuel level from the PCM.
I am thinking that if the PCM is generating a P0462 code(Fuel sending voltage too low) the PCM is either not seeing the correct signal or is unable to process the input it is getting. Since the physical fuel sending unit is showing a resistance rating that is consistent with the amount of fuel in it and by changing the amount of fuel in the tank causes the output resistance to change accordingly I am satisfied that the sending unit is doing what it is supposed to be doing.
Wish i had a spare PCM/SKim/key to test. I will check with the local u pulls in my area, might get lucky!
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post #11 of 36 Old 03-29-2020, 04:40 PM Thread Starter
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Originally Posted by JGCJeep View Post
Have you tested the continuity of the entire circuit? Including the instrument cluster.
Tested voltage and resistance at the fuel pump connector. Tested resistance from fuel sending unit at PCM connections. Tested voltage at PCM.
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post #12 of 36 Old 03-29-2020, 05:32 PM
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Quote:
Originally Posted by JGCJeep View Post
Have you tested the continuity of the entire circuit? Including the instrument cluster.
Tested voltage and resistance at the fuel pump connector. Tested resistance from fuel sending unit at PCM connections. Tested voltage at PCM.
Maybe check for shorted wires.
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post #13 of 36 Old 03-30-2020, 05:52 AM Thread Starter
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Originally Posted by JGCJeep View Post
Maybe check for shorted wires.
Yep. Good idea, make sure that I am not missing simple
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post #14 of 36 Old 03-31-2020, 05:09 AM
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Shouldn't you have a full battery voltage at the fuel pump connector and PCM? I wonder if the 10.7 volts is low because of a bad(loose or corroded) connection somewhere?

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post #15 of 36 Old 03-31-2020, 07:35 AM Thread Starter
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Originally Posted by Bigrigr View Post
Shouldn't you have a full battery voltage at the fuel pump connector and PCM? I wonder if the 10.7 volts is low because of a bad(loose or corroded) connection somewhere?
A very good idea to check power and grounds on this beast in any case. That is what I will be working on next and to check that the battery/ charging system is good.

From the troubleshooting guide provided earlier in this thread by JTEC
They mention greater than 10.4 volts.
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