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You should get a scannner and look how the two senders behave when fuel levels change .
When you fill up your car the left tank sender increase first 0-2.5 volt when your gage moves from 0-50 % and when you fill 50-100% your right sender increase from 0-2.5volt (shown in the table below.
When you consum fuel the voltages will be reduced in the same way when luel level drop. First in the passengerside tank to zero level and secondly in the driver side tank ..
By viewing how the sender behaves you can identify if any of the senders are the problem or the problem is caused by a clogged siphron line/filter
There's a really long but very informative post on the subject here.
You don't mention what year - sending units are different after GM switched the tank design in mid-2003. Unfortunately this new design necessitates dropping the driveline as both tanks have to come out to get to the sending units.
If yours is the older design the job is much less difficult. Unfortunately I'm relatively certain the 19421094 part for the mid-2003 and older cars is in very short supply. RockAuto has removed it from their parts matrix for these cars, meaning whatever their source was for these has dried up. When they were readily available they were only $50 and this job is so easy on early c5s it doesn't make a lot of sense not to do both sides.
You should get a scannner and look how the two senders behave when fuel levels change .
When you fill up your car the left tank sender increase first 0-2.5 volt when your gage moves from 0-50 % and when you fill 50-100% your right sender increase from 0-2.5volt (shown in the table below.
When you consum fuel the voltages will be reduced in the same way when luel level drop. First in the passengerside tank to zero level and secondly in the driver side tank ..
By viewing how the sender behaves you can identify if any of the senders are the problem or the problem is caused by a clogged siphron line/filter
This is how the fuelsenders 97-medio 03 is terminated like this drawing below ..
The fuellevel is causing the sender slipring to change resitance from 40-250 ohm during the full range oft the sender movement
From medio 03 the senders are topmounted in both tanks .like in the C6 fueltanks.
This is how the fuelsenders 97-medio 03 is terminated like this drawing below ..
Actually that diagram applies for the 97-9?. At some point after 98 the right side sensor became identical to the left, and was no longer equipped with the additional 240 ohm resistor that apparently ties from pin C to the in-tank ground. There's info about that in the extensive post I referenced earlier.
Interesting. So the arrow on the 3rd wire of the right must be indicating it's connected to nothing. I don't have a '97 or '98 FSM, I wonder when that changed exactly as there are users who did have something connected on theirs (or so they claimed). Whatever the case, my 2001 had the same 2 wire sensor in both tanks, before and after I replaced them.
Last edited by spfautsch; Apr 8, 2024 at 06:47 PM.
Reason: Clarify my broken grammar
There's a really long but very informative post on the subject here.
You don't mention what year - sending units are different after GM switched the tank design in mid-2003. Unfortunately this new design necessitates dropping the driveline as both tanks have to come out to get to the sending units.
If yours is the older design the job is much less difficult. Unfortunately I'm relatively certain the 19421094 part for the mid-2003 and older cars is in very short supply. RockAuto has removed it from their parts matrix for these cars, meaning whatever their source was for these has dried up. When they were readily available they were only $50 and this job is so easy on early c5s it doesn't make a lot of sense not to do both sides.
You should get a scannner and look how the two senders behave when fuel levels change .
When you fill up your car the left tank sender increase first 0-2.5 volt when your gage moves from 0-50 % and when you fill 50-100% your right sender increase from 0-2.5volt (shown in the table below.
When you consum fuel the voltages will be reduced in the same way when luel level drop. First in the passengerside tank to zero level and secondly in the driver side tank ..
By viewing how the sender behaves you can identify if any of the senders are the problem or the problem is caused by a clogged siphron line/filter
My generic OBD II scanner didn't tell me anything, but luckily I have a Tech 2.
I'm new to it, though, so it took me a little bit to find the right screen with the fuel sensor info. I just filled up the other day, and drove 19.5 miles. Pictures are what I have:
Taken while the engine is running, not just "key on". Where do I go from here?
Hopefully someone with access to the 2004 FSM can chime in with better advice, but it looks like you have an open circuit going to the sensor's contact side (left tank). My process would be checking for a broken dark blue wire to PCM C2 pin 54. If the connector on the pump bulkhead can be reached for removal you could test continuity between that and the PCM connector pin. If that circuit proves good I would assume the wiper contacts on the sensor are worn off, or something else inside the tank.
Dropping the driveline is one of two things:
a) Extremely expensive (assuming you're paying someone to do it)
or
b) Extremely sucky to do unless you have a lift, a transmission jack, etc. Even if you do, it still sucks. Multiply the suckage by 2 if you're doing it on jackstands.
Last edited by spfautsch; Apr 8, 2024 at 07:39 PM.
Have you checked the voltage coming out of the senders AT THE TANKS on the signal wires? This tells you if the senders are working OK.
If they are OK, then I would check the voltage on the signal wires going INTO the PCM. This confirms the wiring from tanks to the PCM are OK.
Then check the voltage on the signal wires coming out of the PCM to the cluster for fuel level.
All of this can be done without dropping the drivetrain etc. You will need to do some digging to get to the PCM behind the passenger side fender though.
You can use a safety pin or sewing pin to probe into the wire and hook a voltmeter to it.
When I look at the voltage values on your drived side sender it is close to 5 volt indicating to me you have a broken circiut between C1:23 and C2:54 .
It could be the sender or some of the connection point .
Please verify/measure signals in the connectors shown on the hardness drawing below .
If you temporaly connect a variable resistor (potentiometer 0-1000 ohm ) in the C412 connector instead of the sender you should be able to simulate a sender signal and check out the wirings between the PCM and the sender when you observe the voltage readings on the Tech2
I'll have to try to dive into it this weekend. With it showing voltage from both sides, could the senders be ok? Like you suspect, a fault in the circuit?
Fuel Sender
full res here
