No lights on switch P38 4.0 AEB175

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slimrick
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No lights on switch P38 4.0 AEB175

#1 Post by slimrick » Tue Feb 26, 2019 8:46 am

Hello all,

I have a 1999 Range Rover P38 (4.0 V8 GEMS). It's fitted with an AEB175 system and has been playing up recently.

A few weeks ago the cut-over from petrol to LPG happened within a minute or so of starting. This then changed to around 10 minutes of running before switching over.
A couple of days ago, all lights on the switch would flash every 30 seconds or so, but no cut-over to LPG would take place.
Now, no lights at all show on the switch.

If I can find a manual for the AEB175 I can start to check the wiring, does anyone have a source for this? Alternatively, any other ideas what else might be causing the issue?

LPGC
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Re: No lights on switch P38 4.0 AEB175

#2 Post by LPGC » Tue Feb 26, 2019 9:56 am

AEB175s can use a reducer temp sensor (to allow automatic switching to gas when the reducer has warmed up a bit) but a reducer temp sensor is very seldom fitted on this type of system.

I use the term 'configured' below, by which I mean options that have been set in the AEB175 using a laptop, software and interface cable between the laptop and AEB175.

They can be configured to switch after X seconds / and or after a certain rpm threshold has been met (in acceleration or deceleration) / or set for full manual control (driver uses the switch to instantly switch between fuels including at engine start). They can be configured to switch to petrol when the LPG tank fuel level sender reflects low LPG level (nearly run out of gas) but they are seldom configured to do that (as tank level readings are haphazard so a likely outcome of using this setting would be the system would switch to petrol when there was still plenty of gas left in the tank).

They can be configured to flash lights on the switch if the unit doesn't see lambda voltage flick (if mixture isn't seen to be correct).

So, not switching to LPG automatically over varying amounts of time can be normal.. the system might be configured not to switch until some condition is met such as rpm switching threshold. And flashing lights can be normal (but would usually point to some tuning work being necessary).

No lights on the switch at all is likely to be unrelated to any of the above and points to an actual problem such as blown fuse, bad wiring, bad ECU.

When these ECUs get old they can forget configuration settings, the first occurrence of this is often when the vehicle battery has been disconnected or is flat, in the early stages of this ECU senility the ECU can usually be reset, re-configured and will work as normal for a good while but eventually the loss of configuration settings starts to occur even when the vehicle battery is good and constantly connected. Loss of configuration settings (and even worse an ECU gone really senile) can cause all sorts of effects including changing switching behaviour, and if configuration settings such as stepper motor position calibration and/or error reporting are affected could lead to the flashing lights.
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slimrick
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Re: No lights on switch P38 4.0 AEB175

#3 Post by slimrick » Tue Feb 26, 2019 1:27 pm

Thanks for the comprehensive reply. I suspect a power / feed issue, and although the fuses look ok I don't particularly trust the standard of work when it was fitted by the previous owner.

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Re: No lights on switch P38 4.0 AEB175

#4 Post by Brian_H » Tue Feb 26, 2019 6:57 pm

Its worth pulling the fuses out of the holders to check the holder hasn't started corroding where you can't see it.

You can find a wiring diagram from the Bigas Pegaso system - I believe this is the same across all of them, Simon can probably confirm. Its available on Tinley tech's website, but they have a typo in the link on the page, so use the link below to find it.

https://tinleytech.co.uk/download/5064/

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Re: No lights on switch P38 4.0 AEB175

#5 Post by LPGC » Tue Feb 26, 2019 7:22 pm

Yeh Bri the wiring is the same on all the AEB175 systems. The only differences between all of them are brand specific software must be used and there are slightly different options in software, nothing to affect wiring.

Just to clarify... Not even the red light comes on the switch when the ignition is turned on? If the red light comes on the switch for a moment when ignition is turned on it could point to lack of rpm signal or incorrect setting for rpm detection in software, the latter could be due to ECU senility.
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Gilbertd
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Re: No lights on switch P38 4.0 AEB175

#6 Post by Gilbertd » Thu Feb 28, 2019 9:57 am

I also have a P38 running an AEB175 Leo (well, two actually), and I've uploaded the manual to Google drive here https://drive.google.com/open?id=1T6Nuy ... hepjmONRJ5 (English starts from page 20).

Failure to switch could mean it has lost it's configuration or, coupled with the intermittent no lights on the switch, is more likely to be a faulty power supply. Check both, permanent (usually taken straight from the battery) and ignition switched (usually taken from the Brown/Yellow fuel injector feed at the engine ECU).
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.

slimrick
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Re: No lights on switch P38 4.0 AEB175

#7 Post by slimrick » Thu Feb 28, 2019 3:55 pm

Gilbertd wrote:
Thu Feb 28, 2019 9:57 am
I also have a P38 running an AEB175 Leo (well, two actually), and I've uploaded the manual to Google drive here https://drive.google.com/open?id=1T6Nuy ... hepjmONRJ5 (English starts from page 20).

Failure to switch could mean it has lost it's configuration or, coupled with the intermittent no lights on the switch, is more likely to be a faulty power supply. Check both, permanent (usually taken straight from the battery) and ignition switched (usually taken from the Brown/Yellow fuel injector feed at the engine ECU).
Superb - I've been trying to track a copy of that down, thank you very much.

I'll do some investigation work this weekend.

Gilbertd
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Re: No lights on switch P38 4.0 AEB175

#8 Post by Gilbertd » Thu Feb 28, 2019 5:39 pm

I have both of mine set to change over on deceleration at 1,200 rpm and leave the switch permanently on gas. Start the engine, blip the throttle and it changes over and runs fine on gas from stone cold. No temperature sensor fitted (in fact, I've never seen a Leonardo installation that had one fitted). If yours is taking longer then it probably has the rpm threshold set far too high, a P38 won't get to 2,000 rpm if driven gently, the box will change up before it gets that high. On my everyday car, a 98 4.0 litre P38, I keep around a quarter tank of petrol in it just in case I run out of LPG but it hasn't needed any petrol putting in it in over 8 months. Even then I only put £20 worth before a long trip on the Continent and wasn't sure I would be able to find somewhere to fill up.
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.

slimrick
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Posts: 4
Joined: Tue Feb 26, 2019 8:40 am

Re: No lights on switch P38 4.0 AEB175

#9 Post by slimrick » Thu Mar 07, 2019 8:50 am

Thanks for your help, and particular thanks to Gilbertd for the manual.

The issue was the ignition switched +12v. This was taken from the output from the heater fan relay in the fusebox. This relay had burned out and hence no +12v output.

Gilbertd
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Re: No lights on switch P38 4.0 AEB175

#10 Post by Gilbertd » Thu Mar 07, 2019 8:58 am

That's a particularly stupid place to take it from, the brown/yellow wire that feeds the common switched supply to the petrol injectors is a far more sensible place to pick it up from. The burnt blower relay(s) is the first sign that your fusebox is failing. Up to 97 they were almost a service item but after a redesign for 97-99 GEMS they are a lot better. Not only will one of your blowers not work but you'll have the chequebook symbol showing on the HEVAC and sooner or later other things will start to fail. Bunging a new fusebox in it is a very good bit of preventative maintenance and not that expensive either. Where in the country are you as I've got a Nanocom for the GEMS P38 and the software for the AEB175 if you need a hand.
'96 Saab 900XS, AEB Leo, sold
'93 Range Rover 4.2 LSE, Lovato LovEco, sold
'98 Ex-Police Range Rover 4.0, Singlepoint AEB Leo, my daily motor
'97 Range Rover 4.0SE, eGas multipoint, a project.....

Proud to be a member of the YCHJCYA2PDTHFH club.

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