Webasto Airtop2000 st problem

[Sam J]

Hi All,

I have a puzzling issue with my AT2000 st.

The crux of the problem is that the fuel pump will not run and throws the 1 flash failure to start code.

If I tap 12v to the pump directly it will work.

If I connect the switching contacts of a relay to the fuel pump wiring, the relay clicks.

If I connect a 12v battery to the switched contacts of the relay and then to the pump it runs and the heater works.

I have replaced the pump ecu with a second hand unit - still not working.

I have replaced the rest of the heater with a second hand unit - still not working.

I have wired the heater directly to a battery with fresh cables - still not working

I am very much out of ideas at this point. The only items that I have not changed are the rheostat, the pump and the wiring loom.

Has anyone else had a similar experience or can offer some direction?

Best regards

Sam

 

[oldiebut goodie]

The fault is not the fuel pump! It is a safety feature that it will not run if the start up conditions are not correct.
I don't know what you mean by "pump ecu" as pumps do not have an ecu.
Rest of the heater has been replaced - exactly what has been replaced?

Check:
• Corrosion on plugs
• Loose plug contacts
• Poor crimp contacts on plugs
• Corroded cables and fuses
• Corroded battery terminals
• Chafed wiring

Then:
Check the voltage as close to the heater as possible AT STARTUP.
Check glow pin resistance against values in the workshop manual.
Check overheating sensor resistance against chart in the manual.

Failing that you will need diagnosis with Webasto software on a PC.

 

[Sam J]

The fault is not the fuel pump! It is a safety feature that it will not run if the start up conditions are not correct.
I don't know what you mean by "pump ecu" as pumps do not have an ecu.

I meant the heater ecu / control unit.

Does the safety feature reduce the voltage to the pump or cut the feed entirely? As I estimate that I am getting around 9v or slightly more at the pump plug.

Rest of the heater has been replaced - exactly what has been replaced?

The whole heater apart from the rheostat, pump and wiring loom. I have fitted a working second hand unit which points to a loom, pump or stat issue.

Check:
• Corrosion on plugs
• Loose plug contacts
• Poor crimp contacts on plugs
• Corroded cables and fuses
• Corroded battery terminals
• Chafed wiring

Then:
Check the voltage as close to the heater as possible AT STARTUP.
Check glow pin resistance against values in the workshop manual.
Check overheating sensor resistance against chart in the manual.

Failing that you will need diagnosis with Webasto software on a PC.

 

[oldiebut goodie]

Does the safety feature reduce the voltage to the pump or cut the feed entirely? As I estimate that I am getting around 9v or slightly more at the pump plug.

Pointing to power supply issue.

Check:
• Corrosion on plugs
• Loose plug contacts
• Poor crimp contacts on plugs
• Corroded cables and fuses
• Corroded battery terminals
• Chafed wiring

Then:
Check the voltage as close to the heater as possible AT STARTUP.
Check glow pin resistance against values in the workshop manual.
Check overheating sensor resistance against chart in the manual.

Failing that you will need diagnosis with Webasto software on a PC.

 

[Sam J]

Check:
• Corrosion on plugs
• Loose plug contacts
• Poor crimp contacts on plugs
• Corroded cables and fuses
• Corroded battery terminals
• Chafed wiring

Then:
Check the voltage as close to the heater as possible AT STARTUP.
Check glow pin resistance against values in the workshop manual.
Check overheating sensor resistance against chart in the manual.

Failing that you will need diagnosis with Webasto software on a PC.

I agree, it does look like a power supply issue.

I removed the live and earth from the main heater plug and made up some fresh cables then connected these to a battery so I know I have a good feed to the heater.

12.7v before the heater starts and drops to 12.5v on startup.

I have no resistance on any of the control wires from the rheostat.

I could have issues with chaffed wiring but I need to dismantle the front of the van to get at it so that will have to wait.

Thanks for your help

 

[oldiebut goodie]

Where is the voltage being measured?
You should have around 1.24KΩ across the blue and white wires from the rheostat. It is virtually impossible for this part to fail.
Where is the heater mounted if you have to dismantle the front of the van? The heater should be mounted in such a position that it can be removed/serviced when required.

 

[Sam J]

Where is the voltage being measured?
You should have around 1.24KΩ across the blue and white wires from the rheostat. It is virtually impossible for this part to fail.
Where is the heater mounted if you have to dismantle the front of the van? The heater should be mounted in such a position that it can be removed/serviced when required.

Voltage is measured at the plug on the heater.

I will check the resistance between the blue and white just to check.

The heater is under the passenger seat and easily accessible but the wiring loom runs under the carpet.

 

[Sam J]

I have spent a little time today setting both of my 2, airtop 2000 st’s up on the bench.

Rewired them to remove the possibility of the loom being at fault and connected them up to a 2 month old battery which was also connected to a charger.

Exactly the same issue as when they’re in the van. The fuel pump wiring will run a relay, bulb and even an injector from a fiesta. But not the Webasto fuel pump.

Does anyone know what the output voltage to the fuel pump from the ecu is supposed to be?

 

[oldiebut goodie]

Check the resistance of the fuel pump - it should be around 5Ω

 

[Sam J]

Check the resistance of the fuel pump - it should be around 5Ω

0.7 ohms

 

[oldiebut goodie]

With that reading you have likely burnt out the pump windings, probably by putting a continuous 12v through it, or if you have backfed 12v to the ecu also blown the ecu. First is the more likely especially if you haven't applied 12v to the pump whilst connected. Pumps work by pulses of 1 to 2.5Hz not continuous voltage.
With a new pump you may well be back to looking for an original fault.

These chinese pumps work OK with the Webastos Heater Fuel Pump 12V 65ml/ For Webasto DP30 86115A 86115B 85106B Quality | eBay

 

[Sam J]

Turns out it was the pump. Ordered an equivalent of the pump listed above (faster delivery) and it fired straight up.

Thanks again