Power Supply Distribution Box/Gateway Module - Eco Stop/Start - Help Understanding

jlglr4

Full Access Member
Joined
Mar 19, 2019
Posts
821
Reaction score
421
Location
Northern California
After three years of no eco stop, no warning light bliss, my light finally turned on. Battery is shot - 10.6v - pretty sure that’s what caused the light. So now I’m trying to get a good understanding of how the Gateway Module and Power Supply Distribution Module (PSDM) works, and looking for a little help. I did read through @Michael Gain ’s helpful post on the traxide system, but I’m still looking for some clarity on a couple of points. Hopefully some of you are better at reading circuits than I am.

Attached is the circuit diagram for the starting system. On the PSDM, there are two battery terminals (Battery 1 and 2), one Load terminal, ground, and then VBatt2, FET diagnostics/Bsense, and LIN. I understand that the LIN is a comm terminal that turns the two mosfets on/off to switch the load between Batt 1 and Batt 2. I’m confused on the FET diagnostics and VBatt2 terminals.

I removed my aux battery, and when my engine is off, I have battery voltage at all three of Batt1, Batt2, and Load terminals. So, with key off, the mosfets must be connecting both Batt1 and Batt2 to the load - that’s the only way I see that I’d have 12v at Batt2. When I turn the key on/engine off or key on/engine on, I have battery voltage only at Batt1 and Load, so the mosfets are isolating the second battery with key on.

I originally thought VBatt2 must be powering the gateway module and FET diagnostics/Bsense was sensing Battery 2 health. But looking at the circuit, the gateway module would have no power with the second battery removed and the ignition on (battery 2 isolated). So, maybe VBatt2 is the sensing circuit and FET diagnostics is something else. But how, then, is power delivered to the gateway module - over the LIN circuits? Can they provide power and comm?

My second question is - how does it charge the second battery? I assume it just switches the mosfets to connect Batt2 to the load when the alternator is running, but not sure.

I find it strange that the car connects the second battery to the main battery/loads when the car is off. Seems like a bad second battery would bring down the main battery. But, I also suspect my PSDS might be faulty, and part of this excercise is trying to figure what might be wrong with it.
 

Michael Gain

Full Access Member
Joined
Dec 8, 2018
Posts
610
Reaction score
279
Location
Clarksville, TN
After three years of no eco stop, no warning light bliss, my light finally turned on. Battery is shot - 10.6v - pretty sure that’s what caused the light. So now I’m trying to get a good understanding of how the Gateway Module and Power Supply Distribution Module (PSDM) works, and looking for a little help. I did read through @Michael Gain ’s helpful post on the traxide system, but I’m still looking for some clarity on a couple of points. Hopefully some of you are better at reading circuits than I am.

Attached is the circuit diagram for the starting system. On the PSDM, there are two battery terminals (Battery 1 and 2), one Load terminal, ground, and then VBatt2, FET diagnostics/Bsense, and LIN. I understand that the LIN is a comm terminal that turns the two mosfets on/off to switch the load between Batt 1 and Batt 2. I’m confused on the FET diagnostics and VBatt2 terminals.

I removed my aux battery, and when my engine is off, I have battery voltage at all three of Batt1, Batt2, and Load terminals. So, with key off, the mosfets must be connecting both Batt1 and Batt2 to the load - that’s the only way I see that I’d have 12v at Batt2. When I turn the key on/engine off or key on/engine on, I have battery voltage only at Batt1 and Load, so the mosfets are isolating the second battery with key on.

I originally thought VBatt2 must be powering the gateway module and FET diagnostics/Bsense was sensing Battery 2 health. But looking at the circuit, the gateway module would have no power with the second battery removed and the ignition on (battery 2 isolated). So, maybe VBatt2 is the sensing circuit and FET diagnostics is something else. But how, then, is power delivered to the gateway module - over the LIN circuits? Can they provide power and comm?

My second question is - how does it charge the second battery? I assume it just switches the mosfets to connect Batt2 to the load when the alternator is running, but not sure.

I find it strange that the car connects the second battery to the main battery/loads when the car is off. Seems like a bad second battery would bring down the main battery. But, I also suspect my PSDS might be faulty, and part of this excercise is trying to figure what might be wrong with it.

Haha dredging up fun memories.

Looking at the diagram again, both batteries and loads are connected by the MOSFETs. Loads lead directly to the fuse box, so batt1 to loads should always be open upon initial start up/ key on.

Batt2 is only connected to batt1 during charging, but it powers loads when start stop is engaged--i.e. at a traffic light with the engine stopped, your accessories are powered by the second battery.

Now, vbatt2 monitors the voltage of battery 2. If it is low, the vehicle disables start stop and powers accessories from batt1.

FET diagnostics only monitors the operation of the MOSFET gates. If one is stuck open or closed/ burns out, the system should default to allow batt1 to power everything, and your start stop light will illuminate.

Now, that I think through this more, the LIN should be a two way communication link. It reports information to the gateway module, but also receives commands to open and close MOSFETs accordingly.

The gateway module receives it's power from the battery 1 either directly or through another module ( I think), but not from the psdb.

Hope that helps!
 

jlglr4

Full Access Member
Joined
Mar 19, 2019
Posts
821
Reaction score
421
Location
Northern California
Thanks. Looks like one pin on the PSDB was not drawn on the diagram - PIN 1, appears to connect to the central junction box, so that must power the gateway module.

I’m still perplexed about seeing 12v on the Batt2 terminal when the engine is off and auxiliary battery removed. Seems like the Batt2 terminal should be isolated when the engine is off. Maybe this is a mode of failure of the PSDB.

Not sure what I’m going to do with all this info yet. For now, probably just hook up a less expensive motorcycle battery and see what happens.
 

cannondale900

Active Member
Joined
Nov 13, 2019
Posts
29
Reaction score
10
Location
Chicagoland
Thanks. Looks like one pin on the PSDB was not drawn on the diagram - PIN 1, appears to connect to the central junction box, so that must power the gateway module.

I’m still perplexed about seeing 12v on the Batt2 terminal when the engine is off and auxiliary battery removed. Seems like the Batt2 terminal should be isolated when the engine is off. Maybe this is a mode of failure of the PSDB.

Not sure what I’m going to do with all this info yet. For now, probably just hook up a less expensive motorcycle battery and see what happens.
I know you are on a fact finding expedition regarding the PSDS but I had this Exide EK151 arrive from this European seller within a week of purchasing. The unit that showed up at my house was manufactured Dec 2020 mfr date and within 30 mins of driving the start/stop and auxiliary systems were functioning normal again along with secondary battery system readings, etc that I could see per GAP tool.

https://www.ebay.com/itm/152872413814?epid=1244502397&hash=item2397e7ea76:g:M0YAAOSw2tFaYckz
 

Michael Gain

Full Access Member
Joined
Dec 8, 2018
Posts
610
Reaction score
279
Location
Clarksville, TN
Thanks. Looks like one pin on the PSDB was not drawn on the diagram - PIN 1, appears to connect to the central junction box, so that must power the gateway module.

I’m still perplexed about seeing 12v on the Batt2 terminal when the engine is off and auxiliary battery removed. Seems like the Batt2 terminal should be isolated when the engine is off. Maybe this is a mode of failure of the PSDB.

Not sure what I’m going to do with all this info yet. For now, probably just hook up a less expensive motorcycle battery and see what happens.

Are you seeing 12v with ignition off and engine off? Or ignition on and engine off? If the former, that is worrisome. If the latter, it makes sense as the MOSFET is opening in preparation for the alternator to charge batt 2.
 

greiswig

Full Access Member
Joined
Mar 1, 2021
Posts
480
Reaction score
165
Location
Oregon
I know some circuits will show voltage at a terminal when using a high-impedance voltmeter, but in reality there's no current there to speak of. Possibly a measurement issue? Or can you actually power a test bulb at both terminals with the engine off?
 

jlglr4

Full Access Member
Joined
Mar 19, 2019
Posts
821
Reaction score
421
Location
Northern California
I know you are on a fact finding expedition regarding the PSDS but I had this Exide EK151 arrive from this European seller within a week of purchasing. The unit that showed up at my house was manufactured Dec 2020 mfr date and within 30 mins of driving the start/stop and auxiliary systems were functioning normal again along with secondary battery system readings, etc that I could see per GAP tool.

https://www.ebay.com/itm/152872413814?epid=1244502397&hash=item2397e7ea76:g:M0YAAOSw2tFaYckz
Thanks - that’s a good price. From Latvia…think it’s real? Probably is - that Exide is probably the same as other batteries sold here for motorcyles - just without the terminal modifications (you can see several of the motorcycle batteries are made with the round terminals and then square terminals are soldered on top).


Are you seeing 12v with ignition off and engine off? Or ignition on and engine off? If the former, that is worrisome. If the latter, it makes sense as the MOSFET is opening in preparation for the alternator to charge batt 2.
I’m seeing 12v (actually 12.6v) with ignition and engine off. As soon as I hit the ignition, it drops to zero. Engine on - still at zero. Engine off - stays at zero for about 2-3 minutes, then back to 12v.

When I first pop the hood, I’m getting zero volts at batt2 and I can see a drop in battery voltage - probably some circuits coming alive when the hood sensor triggers. When the voltage recovers (things going back to sleep), the voltage appears again at Batt2.

So, maybe its more accurate to say that Batt2 has voltage with no second battery when the car is asleep. Any other time, it appears to have no voltage.

I know some circuits will show voltage at a terminal when using a high-impedance voltmeter, but in reality there's no current there to speak of. Possibly a measurement issue? Or can you actually power a test bulb at both terminals with the engine off?

Hmmm….I don’t know. The voltage is slightly less than battery voltage, like 12.4 vs 12.6. It will not power a test bulb - so not much amperage (although, in retrospect, I probably should not have done that - not sure if drawing amps at the wrong time can cause damage - still getting voltage, so didn’t seem to fry anything). Wondering if I’m measuring some kind of reference voltage being applied from the monitoring circuit?
 

cannondale900

Active Member
Joined
Nov 13, 2019
Posts
29
Reaction score
10
Location
Chicagoland
Thanks - that’s a good price. From Latvia…think it’s real? Probably is - that Exide is probably the same as other batteries sold here for motorcyles - just without the terminal modifications (you can see several of the motorcycle batteries are made with the round terminals and then square terminals are soldered on top).

It is real indeed. Others on this site and Jaguar forums have purchased from this seller without issue and it arrives quickly considering it is coming from Eastern Europe. The secondary battery in our cars is, in fact, the Exide EK151 with a JLR label on it. I checked out the regular website of this Ebay seller and they are a legit auto parts retailer. I didn't really feel like messing with the terminals on a more readily available equivalent battery, nor re-terminating the leads in the car.
 

jlglr4

Full Access Member
Joined
Mar 19, 2019
Posts
821
Reaction score
421
Location
Northern California
@cannondale900 Thanks for the info. Your right - better than messing around with the terminals. I’ll give it a try. I don’t expect it will make my eco work, as that hasn’t worked for a long time - even when the last battery was new. I like it that way. But, who knows with this car.
 

jlglr4

Full Access Member
Joined
Mar 19, 2019
Posts
821
Reaction score
421
Location
Northern California
Just reporting back - bought that Exide battery cannondale900 recommended on ebay (link above). Arrived quickly and appears to be brand new and in good health. Installed, my light is now off and my eco start/stop remains non-functional - which is a win. Wish I could tell others how to disable it, but it remains a mystery to me.

Interesting bit though: when I installed the new battery, the clock immediately switched to 24 hr time. The mysterious switching of time formats has been noticed by many for no obvious reason. I have had it happen once before out of the blue. Not sure why installing the new battery triggered it, or what it means, just thought I’d mention.
 

Latest posts

Forum statistics

Threads
35,624
Posts
210,390
Members
29,902
Latest member
saopesoko
Top