Thread: Reverse Reading on Fuel Pump Module - In-tank Pump

Originally Posted by Lionelgee

Hello All,

Just wondering whether there is some way to reverse the resistance reading coming from the fuel tank sender and its connection to the fuel gauge? I had to replace the fuel pump in my daily driver - sorry its a VY Commodore.

Instead of reading 1/4 of a tank the new sender is putting out a reading that is more than full. I read a comment posted on an online shop that a similar thing happened to another bloke. The new fuel module he bought did the same as my replacement module does - read over full when it should be just a 1/4 tank. The bloke wrote that the polarity of the resistance in the fuel sender unit was reversed when it sent a signal to the fuel gauge. He still had his old fuel module and took the sender off that unit and fitted it to the new fuel module and the fuel gauge was accurate. Problem solved! Well for him....

I have received a replacement fuel new pump module under warranty because I thought the previous new pump module was faulty. I thought why should I fit an old sender to a new fuel pump! What I bought should be fit for purpose out of the box. Anyway - today the newly exchanged and installed fuel pump module repeated the same issue - instead of reading 1/4 it is bending the needle at the full stop pin on the gauge!!!

Today's effort was the third time I dropped the tank and fitted it again. To be able to try the technique of fitting the old sensor to a new pump module that solved a bloke's similar issue with his tank it means dropping the tank for a forth time.

In case you are wondering - I dropped the tank to take the old fuel module out and fitted the new fuel module - tank drop Number 1. When I noticed that the fuel gauge was faulty I dropped the tank again just to make sure that I had not incorrectly fitted anything. This was before reading the post from the bloke who fitted an old sender to a new fuel module - so that made tank drop Number 2. Then when the replacement fuel module arrived I dropped the tank again today, for tank drop Number 3. I really do not want to make it Tank 4.

I ordered a 2004 VY Commodore fuel module. My Commordore was made in October and is a Series II. I have the feeling that maybe I have been sent a Series I before October 2004 module and the fuel sender works differently Between a Series I and Series II?

It has me rather annoyed - as it is another day wasted with very unsatisfactory results - again!

It would be good if there is some electronic way of tapping into the wiring circuit and tricking the sender to be able to send an accurate signal to the fuel gauge by tapping into the wiring somewhere. This would eliminate the need for tank drop Number 4 from happening.


Kinds regards
Lionel

I've never delved into the vehicle wiring setups of such systems, but with industrial control these type of things are usually just a variable resister with a center tap sending off the analog signal to god knows where.

If it's backwards - changing the polarity of the supply wires will fix it for you.
If the unit is earthed internally, too bad, you're stuffed. If the plug wiring has three wires you could be in luck. depin and swap the voltage supply wires. this should fix the issue.

It's better to fix it on the pump, so any pump swaps by future owners they won't have to go through this again.
But it's a VY commodore, the ECU will be long dead by then and write the car off anyway. Don't ask me how I know this.

Hello All,

After fitting the replacement fuel pump assembly that was covered under warranty I found the new unit caused the same incorrect reading in the fuel gauge. The needle tries to bend the little pin at the furthest reach of the gauge showing full when it should be reading only 1/4. So I revisited the online supplier and rechecked with their "Suitability" checker and it said that the fuel assembly was suitable for my car.

With the gauge reading incorrectly on both units I sought out a new source of information and I contacted the manufacturer by email. My email included the Commodore's VIN. A couple of hours later I received an email back stating that the parts that I was sent are not the correct ones for the car. I was given the correct product code and also informed that the company will not be producing any more of those units until next year!

I went back to the supplier's website and typed in the correct product number. The result came back as 'out of stock'. Luckily, there were other suppliers who did have the manufacturer-specified correct fuel assembly in stock. I was then contacted by the supplier and I was asked to return the two incorrect fuel assemblies to them. I wrote back to them to say that I needed to keep one unit in the car because it needs a fuel pump to be able to drive. Some days after I posted the unit back the supplier informed me that they will send the correct replacement unit once the part I sent arrives at their location. Having already checked their inventory and finding that the part was shown as 'out of stock" I got the company to check. An email arrived stating that the part is available in their stock. Speed forward two more days - an email arrives - our apologies there was an incorrect count taken and we now cannot provide your with the correct part. I will be sent a refund instead once the part that I have sent arrives.

If I had gone ahead and ordered the correct part from another company it would now either be on its way to me or already been installed in my car and I would know how much fuel is in the tank. Remember that it was the company's 'Suitability Checker' that said that the part I ordered was suitable for my car - when it really was not.

Well - the new correct part is ordered from another company and it is on its way. Fingers crossed that it will be forth time dropping the fuel tank is the lucky time.

Kind regards
Lionel

Hello All,

Well for something that started with me ordering what the online retailer stated in their "parts suitability' checker was the suitable fuel assembly back on the 12 May, 2022, today I fitted the third replacement fuel pump assembly. This worked out to involve my dropping the Commodore's fuel tank four times. I dropped it the second time to make sure I had not created the problem with the inaccurate fuel gauge reading by accidentally connecting the pipes and wires to the incorrect outlets. It turns out I had not connected anything incorrectly - at least this possibility was eliminated from my check-list.

Well, after fitting the third fuel assembly which the manufacturer's stated was the correct one for the Commodore's VIN I was greeted by two things on the instrument cluster I have not seen since May...

Those two parts of the instrument cluster are working perfectly. The new fuel pump sings along. The fuel pump was faulty back in May and needed to be replaced. Until its removal the original fuel pump assembly and fuel level arm were the most the most accurate I have had on any car that I have owned. The supposedly "suitable" parts had a different fuel level arm unit that reversed the reading of what fuel was in the tank. Now I have a fuel pump that is functioning properly and an accurate fuel gauge and kilometres to empty notification. Hooray!

Kind regards
Lionel