Fuel Gauge Empty & Low Fuel Warning Light Permanently On – Electrical Test Results Included

[tyclyd]

I'm hoping for some hive mind technical input from anyone familiar with the R1150GS Adventure fuel sender and warning light system. The bike is a 2002 R1150GSA with approximately 250,000–260,000 miles on the clock and after a run went to start today and ... bingo...

The original fuel sender / pump plate assembly failed in around 2012 after approximately 110,000 miles and was replaced with a genuine BMW pump plate and sender assembly. The current assembly is therefore around 14 years old and has covered approximately 140,000–150,000 miles.

Symptoms

• Fuel gauge displays no bars from the moment the ignition is switched on.
• Amber low-fuel warning light is permanently illuminated.
• Tank currently contains approximately 20 litres of fuel.
• Bike starts, runs and rides perfectly.
• Fuel pump primes and operates normally.
• No fuel leaks.
• Rocking the bike makes no difference to the gauge reading.
• When the bike is rocked, movement can be heard from within the tank, suggesting the float mechanism is not completely seized.
• Original RID is still fitted.
• The RID appears to be functioning because the temperature gauge works normally and the low-fuel lamp is being driven.

Electrical Tests

The following resistance readings were taken on the 'tank side' of the four-pin connector with the ignition switched off. Tank Side Resistance Measurements

| Pins | Resistance
| Pin 1 to Pin 2 | 0.6 Ω
| Pin 1 to Pin 3 | 6.56 Ω
| Pin 1 to Pin 4 | 0.50 Ω
| Pin 2 to Pin 3 | 5.52 Ω, slowly falling
| Pin 2 to Pin 4 | 1.0 Ω
| Pin 3 to Pin 4 | 4.2 Ω

Bike Side Resistance to Ground

| Pin | Resistance
| Pin 1 to Ground | 1.0 Ω
| Pin 2 to Ground | 1.1 Ω
| Pin 3 to Ground | 6.88 Ω
| Pin 4 to Ground | 1.1 Ω

Bike Side Voltage to Ground (Ignition On)

| Pin | Voltage |
| Pin 1 to Ground | 0 V
| Pin 2 to Ground | 0.9 V
| Pin 3 to Ground | 7.9 V
| Pin 4 to Ground | 12.2 V

Additional Information

One of the pump plate retaining bolts is already loose, which makes me reluctant to disturb the assembly unnecessarily. She is not leaking and i don't want her to start...

At present she runs perfectly, the fuel pump is operating normally and there are no fuel leaks. Given the age of the pump plate assembly and the condition of the retaining hardware, I do not want to risk damaging the seal or creating a fuel leak where none currently exists - the plate repair and bolt replacement can wait until its snowing and cold up here...

I can quite happily live without the fuel gauge and simply use the trip meter, so I am not looking for a reason to dismantle the tank. Rather, I am looking for any advice from those familiar with the R1150GS Adventure fuel sender system to ensure that I have not overlooked something obvious in the electrical testing.

So... my question is

Based on the resistance and voltage readings above, does anything stand out as a known fault pattern on the R1150GS Adventure?

In particular, do the readings suggest:

A failed fuel level sender?
A failed low-fuel warning circuit?
An internal pump plate wiring fault?
An earth/ground fault?
Something else entirely?

Any technical interpretation of the readings would be greatly appreciated before I consider disturbing the pump plate assembly.

Ta

 

[Ian J Hartley]

Try pulling the fuel level damping module from the fuse box.

 

[Ian J Hartley]

Tank connector

| Pins | Resistance
| Pin 1 to Pin 2 | 0.6 Ω resistance across the motor (not relevant ignore)

| Pin 1 to Pin 3 | 6.56 Ω maximum resistance across the sender. This looks about right.

| Pin 1 to Pin 4 | 0.50 Ω resistance across the low level switch which only closes when tank near empty.
This value is wrong it should be showing an open circuit

| Pin 2 to Pin 3 | 5.52 Ω, slowly falling. Measurement across motor and fuel sender unit (ignore)

| Pin 2 to Pin 4 | 1.0 Ω measurement across motor and low level switch (not relevant ignore)

| Pin 3 to Pin 4 | 4.2 Ω measurement of fuel sender wiper across switch this measurement is also
wrong, it Should be Open circuit.

All the indications are that your tank is empty so based on your values it looks like either your float is stuck down at empty position, or the float is no longer floating.

Pulling the fuel level damping unit should put the low fuel warning light out, and it should no longer operate.

 

[tyclyd]

Thank you for that. I have done as suggested. The module is:

• BMW 61 35 2 306 365
• VDO 2800245

Prior to removal:

• Fuel gauge displayed no bars.
• Amber low-fuel warning light was permanently illuminated.

With the module removed:

• The amber low-fuel warning light extinguished immediately.
• The RID fuel display remained unchanged with no bars displayed.

After refitting the module:

• The amber low-fuel warning light remained off.
• The RID fuel display still showed no bars.
• The temperature display on the RID continues to function normally.

The bike has now been through several ignition cycles and the low-fuel warning light remains extinguished.

This seems to suggest that the damping module is influencing the warning lamp behaviour, although the RID is still not receiving (or displaying) a valid fuel level signal.

Does this additional information alter anyone's interpretation of the resistance and voltage readings posted earlier?

In particular, would a faulty damping module be capable of producing a permanently empty fuel gauge display, or does the fact that the RID still shows no bars point more strongly towards the sender/pump plate side of the circuit?

 

[Steptoe]

There have been similar problems posted in the past…
Some of them were cured by wiping clean the rheostat which the float arm operates on ..

 

[Ian J Hartley]

The damping unit does control the low fuel light. Without it, the fuel light will be flashing on and off with the movement of the bike as fuel sloshing around in the tank. This would be distracting to the rider, so the damping unit will only display the low fuel light after it senses a sustained period of low fuel.

The fuel level damping has no effect on the RID fuel bars displayed. That is direct from the resistance value of the sender unit.

I’m still leaning towards your sender unit.

Disconnect the fuel tank connected, and on the bike side of the connection if you short pins 1 and 3 you should see full fuel bars on your RID.

 

[tyclyd]

There have been similar problems posted in the past…
Some of them were cured by wiping clean the rheostat which the float arm operates on ..

Cheers Steptoe, yes, that was my initial thought but I cant get into the tank at the moment. Tank off, plate out, clean and repair of the tank bolts will be on the cards for the winter... at the moment I am fuel tight with 5 working bolts holding on the pump plate

 

[Steptoe]

Cheers Steptoe, yes, that was my initial thought but I cant get into the tank at the moment. Tank off, plate out, clean and repair of the tank bolts will be on the cards for the winter... at the moment I am fuel tight with 5 working bolts holding on the pump plate

Believe me there are many many bikes riding around with only 5 nuts/bolts holding the plate onto the tank.
I personally know of two leak free (for now) fuel tanks with only 4 bolts, but the broken studs are opposite each other, which helps

 

[tyclyd]

Tank connector

| Pins | Resistance
| Pin 1 to Pin 2 | 0.6 Ω resistance across the motor (not relevant ignore)

| Pin 1 to Pin 3 | 6.56 Ω maximum resistance across the sender. This looks about right.

| Pin 1 to Pin 4 | 0.50 Ω resistance across the low level switch which only closes when tank near empty.
This value is wrong it should be showing an open circuit

| Pin 2 to Pin 3 | 5.52 Ω, slowly falling. Measurement across motor and fuel sender unit (ignore)

| Pin 2 to Pin 4 | 1.0 Ω measurement across motor and low level switch (not relevant ignore)

| Pin 3 to Pin 4 | 4.2 Ω measurement of fuel sender wiper across switch this measurement is also
wrong, it Should be Open circuit.

All the indications are that your tank is empty so based on your values it looks like either your float is stuck down at empty position, or the float is no longer floating.

Pulling the fuel level damping unit should put the low fuel warning light out, and it should no longer operate.

Thank you Ian, further update, I disconnected the tank connector and briefly shorted pins 1 and 3 on the bike side of the loom with the ignition on. The RID immediately displayed a full tank indication. This would appear to confirm that the RID, associated wiring and fuel gauge display circuitry are functioning correctly, and that the fault lies on the tank side of the connector. Given Ian's interpretation of the resistance measurements, I'm now leaning towards a sender, low-level switch or float-related fault within the pump plate assembly.

 

[tyclyd]

Further Update

Following Ian's suggestion, I disconnected the tank connector and briefly shorted pins 1 and 3 on the bike side of the loom with the ignition on.

The RID immediately displayed a full tank indication.

To me, that would appear to confirm that:

• The fuel gauge section of the RID is functioning.
• The wiring between the tank connector and the RID is functioning.
• The fuel gauge is capable of displaying fuel level information when presented with a valid signal.

I have also removed the fuel level damping module (BMW 61 35 2 306 365 / VDO 2800245). With the module removed the low-fuel warning lamp is extinguished, although the RID still displays no fuel bars.

My understanding from the comments above is that the damping module controls the low-fuel warning lamp behaviour but has no influence on the RID fuel bar display.

Question 1

Is there any reason not to continue riding the bike with the damping module removed while I continue fault-finding, or does it serve any other function beyond warning lamp damping?

Question 2

As a further test, I am considering substituting a range of known resistances between pins 1 and 3 on the bike side of the connector to see how the RID responds.

My thinking is that if:

• 0 Ω (direct short) = Full tank
• 1 Ω, 2.2 Ω, 3.3 Ω, 4.7 Ω, 6.8 Ω etc. progressively reduce the displayed fuel level

then that would further confirm that the RID and bike-side wiring are operating correctly and that the fault lies entirely on the tank side of the connector, whether that be the sender, rheostat track, float, low-level switch or associated wiring.

Does that sound like a valid diagnostic approach, or am I overlooking something obvious?

Many thanks for all the help so far.

 

[Ian J Hartley]

Further Update

Following Ian's suggestion, I disconnected the tank connector and briefly shorted pins 1 and 3 on the bike side of the loom with the ignition on.

The RID immediately displayed a full tank indication.

To me, that would appear to confirm that:

• The fuel gauge section of the RID is functioning.
• The wiring between the tank connector and the RID is functioning.
• The fuel gauge is capable of displaying fuel level information when presented with a valid signal.

I have also removed the fuel level damping module (BMW 61 35 2 306 365 / VDO 2800245). With the module removed the low-fuel warning lamp is extinguished, although the RID still displays no fuel bars.

My understanding from the comments above is that the damping module controls the low-fuel warning lamp behaviour but has no influence on the RID fuel bar display.

Question 1

Is there any reason not to continue riding the bike with the damping module removed while I continue fault-finding, or does it serve any other function beyond warning lamp damping?

Question 2

As a further test, I am considering substituting a range of known resistances between pins 1 and 3 on the bike side of the connector to see how the RID responds.

My thinking is that if:

• 0 Ω (direct short) = Full tank
• 1 Ω, 2.2 Ω, 3.3 Ω, 4.7 Ω, 6.8 Ω etc. progressively reduce the displayed fuel level

then that would further confirm that the RID and bike-side wiring are operating correctly and that the fault lies entirely on the tank side of the connector, whether that be the sender, rheostat track, float, low-level switch or associated wiring.

Does that sound like a valid diagnostic approach, or am I overlooking something obvious?

Many thanks for all the help so far

Question 1
I can see no reason for not removing the fuel damping unit. As I’ve already mentioned, it only controls the fuel warning light and is there to prevent fuel light flashing when the low fuel sloshing around the tank

Question 2
Nothing wrong with what you propose, varying the resistances across pins 1 and 3 will alter the number of bars displayed. But as you will have power on the bike for your testing, Just be careful not to accidentally touch pin 2 which will go live for the few seconds after ignition turned on (fuel pump/fuel rail priming). To be safe I would pull fuse 6 which controls the fuel pump relay.

The low level switch on your bike is built into the fuel sender unit, it’s at the end of the track and is not a separate switch as those fitted to the R series.