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Discussion Starter #1
My last gasp to fix my faulty temp gauge ('02 P38 Thor) is the serial link from the BECM to cluster but I can't seem to find the right plug/wires from the BECM on Rave. Any help would be appreciated. For what it's worth my temp gauge only registers bottom of the blue. I've checked/replaced the temp sensor, swapped BECM's, swapped instrument clusters. And even rewired the sensor black ground and directly wired the green wire to the BECM with no luck. I can get a OBDII reading but nothing to the cluster gauge. I do get correct ohm reading from the sensor.
 

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on a D2 the temp gauge is driven by the ECU, not the BECM. Pin C0636-44. I recall the fixed frequency is around 180 Hz, but I can't find that in the manual.
Rave said:
Coolant temperature gauge signal The ECM controls the temperature gauge in the instrument cluster. The ECM sends a coolant temperature signal to the temperature gauge in the instrument cluster in the form of a PWM square wave signal. The frequency of the signal determines the level of the temperature gauge. Conditions The ECM operates the PWM signal under the following parameters: l -40 °C (-40 °F) = a pulse width of 768 µs. l 140 °C (284 °F) = a pulse width of 4848 µs
I don't know if the P38 is different, I can't see why it would be and the signal to the gauge cluster is linear, the gauge cluster does voodoo to the data and creates all the gauge deadbands
 

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Discussion Starter #3
I think it is slightly different on the P38 - 4 wires from the sensor, two go to the ECU, other two go to the BECM which then goes to the cluster via serial link. I can pull a temp reading from my OBDII port (which comes from the ECU). But zero reading on the gauge. I tried everything else. About ready to see if I can hook up the temp gauge directly to the sensor and bypass the BECM all together
 

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I used to have the engine ecu sids but my computer died and so did the document, according to the wiring the temp gauge is pulse with modulating signal thru the engine ecu not the becm. I think you can find the diagram on rave but the bosh sids is much more complete and in depth.
 

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The serial link goes over 4 wires - and to the instrument cluster they are doubled up aswell so there is redundancy.All of the message center communication, most of the fault lights, and also the fuel gauge all go over the serial link aswell - so if all of that is working fine, then the issue is not there. If the serial link to the cluster went down then I would expect to see more failures than just an under-reading temp gauge.The OBD II reading will be coming from the engine ECU I would imagine, which uses the other sensor in the housing. If you have access to a Nanocom or the likes which will talk to the BECM, then you can check the temperature that it thinks the engine is at in the BECM->INPUTS->ENGINE GEARBOX window.If you don't then - where did you check the resistance of the sensor that feeds the BECM? At the sensor end, or the BECM end? It could be that the sensor is OK, but the physical wire to the BECM has a problem in it so that it's not showing the proper resistance at the BECM end and that is causing the issue. I would use a multimeter on resistance setting to see what the resistance of the wire is from the sensor connector to the BECM. If this is high resistance (the wire goes through a connector under the coolant header tank!) then it will throw off the reading.Hope this helps,Marty
 

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Discussion Starter #6
The serial link goes over 4 wires - and to the instrument cluster they are doubled up aswell so there is redundancy.All of the message center communication, most of the fault lights, and also the fuel gauge all go over the serial link aswell - so if all of that is working fine, then the issue is not there. If the serial link to the cluster went down then I would expect to see more failures than just an under-reading temp gauge.The OBD II reading will be coming from the engine ECU I would imagine, which uses the other sensor in the housing. If you have access to a Nanocom or the likes which will talk to the BECM, then you can check the temperature that it thinks the engine is at in the BECM->INPUTS->ENGINE GEARBOX window.If you don't then - where did you check the resistance of the sensor that feeds the BECM? At the sensor end, or the BECM end? It could be that the sensor is OK, but the physical wire to the BECM has a problem in it so that it's not showing the proper resistance at the BECM end and that is causing the issue. I would use a multimeter on resistance setting to see what the resistance of the wire is from the sensor connector to the BECM. If this is high resistance (the wire goes through a connector under the coolant header tank!) then it will throw off the reading.Hope this helps,Marty
Thanks. I replaced the wires from the sensor to the BECM and still no luck. I did check the ohm reading before as well from the sensor to BECM (green wire) and it was where it should be reading.
 

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That is somewhat strange then. What resistance are you getting at the BECM, out of interest, and at what temperature you read on OBD II diagnostics? If you can give me the resistance, I'll cross check it with my 2001 and just see if they are inline. As I mentioned - I doubt it's the serial link which is causing it, as these wires are all doubled-up for redundancy, and also other functions wouldn't be working properly. But if you want to check them, then the wire colours are: Black/Green, Red/Green, Orange/Green, and Light Green. There will be 2 of each colour at both the instrument cluster and BECM ends.If it had just been that BECM that was giving an issue, then I would have said to check the engine type - as I've seen before that if you set a BECM to 'Late EDC' then it will start/run a Thor vehicle (as the immobilisation strategies are the same) but the temperature gauge reads different, as the resistance on the sensor is different between petrol/diesel vehicles. I know this isn't as much of a likelihood in the state as you don't have diesel P38's - but it's something that could have been toyed with by someone previous and you wouldn't actually notice any difference in vehicle running. That idea is out the window anyway, given that it did the same on a different BECM. If you can get the resistance and temperature for me, I'll do a check on it against my Thor and see how they compare...
 

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Discussion Starter #8
I wonder if I am pulling ohm from the wrong wire on the green plug (note pic) as not I get no ohm reading (temp was at 157 F).

IMG_9098.JPG

Not sure the pic is working. Here's a link to it...

https://ibb.co/h3kqCT
 

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I can't see the image - there is an issue with the forum displaying them, I think.

The wire should be the Green one on Pin 19 of C1289. I think you will probably need to pull the connector from the BECM to read it accurately, and some multimeter probes are too fat to make good contact with the pins, so I usually use a piece of thin wire to stick into the pin hole and then probe that. You should get a reading between that pin and any ground point - the one at the back of the BECM would be the best one to use as that will be what the BECM references from.

At 157F, I would be expecting to see (if it's a 10K NTC thermistor - which seem to be the most common) between 1.7 and 2.1K ohms
 

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Discussion Starter #10
I may have found the issue. I did have the correct wire/pin on the plug to the BECM and I got no reading. I shaved off the green wire a bit on the plug to the temp sensor and I got no reading. The sensor is new (previous one had the same issue). I think the wire harness to the plug is the issue. I think I was pulling an ohm reading from the wrong wire on the plug to begin with (the one going to the ECU).
 

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That is most likely to be the issue - you can check it at the connector under the coolant tank - pin 12 on the big round connector. If you check it from the BECM to that connector, and then the other side of the connector to the sensor connector will tell you which half of the loom the issue resides in.

If it's on the sensor end of the loom, then I'd be looking at the end towards the sensor connector as they can get coolant on there and it can corrode the wiring. Also, the connector under the coolant tank can get coolant into it if it's ever spilled over it can get in there and give issues.

It could also be an issue with the grounding wire to the sensor (for the BECM side), but you should be able to check the continuity of black wire in the connector to ground.

Marty
 

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No wish to hijack the thread here but my enquiry is slightly relevant to some of the content. Particularly for @marty_nz, @robertf, and @95classiclwb; do you have any detail on the serial comms between the BECM and instrument cluster? Data rate, parity, stop bits etc...

I'm also interested in the comms detail between the engine ECU (all models) and BECM, and data comms from the OBD2 port to BECM. Although I've looked for this sort of stuff over the years, and have a small library on it, I've never really got to the 'holy grail' of information that has been tantalisingly referenced on several occasions...

Thanks, and well done on the fault-finding @Rover-ABQ,
 

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No wish to hijack the thread here but my enquiry is slightly relevant to some of the content. Particularly for @marty_nz, @robertf, and @95classiclwb; do you have any detail on the serial comms between the BECM and instrument cluster? Data rate, parity, stop bits etc...

I'm also interested in the comms detail between the engine ECU (all models) and BECM, and data comms from the OBD2 port to BECM. Although I've looked for this sort of stuff over the years, and have a small library on it, I've never really got to the 'holy grail' of information that has been tantalisingly referenced on several occasions...

Thanks, and well done on the fault-finding @Rover-ABQ,

..you can do that with serial data sniffer tools, record whole signal transfer with same timestamp and analyze recorded data streams/extract needed info..i did that some time back with EAS (issues with driver)...
 

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..most direct approach to do this would be use of oscilloscope where you can directly observe baud rate and voltage of signal(modern oscilloscopes and even multimeters offer automatic determining of baud rate). But in case one you have doesn't, just do it manually, but measuring period of carrier wave, seen by oscilloscope..cant go wrong with that..
 

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No wish to hijack the thread here but my enquiry is slightly relevant to some of the content. Particularly for @marty_nz, @robertf, and @95classiclwb; do you have any detail on the serial comms between the BECM and instrument cluster? Data rate, parity, stop bits etc...

I'm also interested in the comms detail between the engine ECU (all models) and BECM, and data comms from the OBD2 port to BECM. Although I've looked for this sort of stuff over the years, and have a small library on it, I've never really got to the 'holy grail' of information that has been tantalisingly referenced on several occasions...

Thanks, and well done on the fault-finding @Rover-ABQ,

No, but a logic analyzer and some time swapping fixed resistors to identify what data is what sensor would knock it out quickly. Saleae is the cheap go to these days.
 

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Thanks for the followup guys, I was particularly interested in anything anyone had come across or knew off-hand but still it would seem the detail remains elusive :)

Although I have all of these tools and more I was trying to avoid all the probably unnecessary work in reinventing the wheel, and would rather have concentrated on other (Land Rover) things that I may be better suited to. Never mind, I'll keep up the hunt and/or when I can find time will get the gear out to have a look at what's going on.

@Ecco Thanks for your note; I did start looking at EAS comms in the weekend but it's still early in that research so it's good to know someone else has done it successfully.
 

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@private_user

issue i have had was 'dancing' eas, where car acted like randomly going up/down on each corner so it looks like its rigged for some sort of dance..it turned out to be an driver so i used that opportunity to scan all control signals coming in/out on signal analyzer...it appears to be very simple 10V signal followed by quadrature drive signal for each valve block coil where initial drive signal has 50ms pause then quadrature signal goes some 25ms 10V pulse, if i remember properly..very easy to build with power mosfets..original idea was to actually record complete communication between BECM and each of ECU units and basically redesign becm, but i just barely started as without donor vehicle which can be hooked to instruments, its hard to do on a truck i use every day...maybe some time january when i may obtain one, quite literally, brand new P38, i may just continue.. :)
 

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@Ecco Thanks for the headsup. I've done what you're wanting to do insofar as I've got a development machine I can toy with, without disturbing the daily driver.

At this stage I'm more interested in the EAS control ECU, and the BECM (incl control data), rather than the valve driverset. I'd vaguely thought about SS relays should it be necessary, but haven't got anywhere near that stage - it's simply been signal level stuff I've been working on as I see this being much the more complex item than something to simply drive solenoids. Your comments appear to confirm this view :)

I envy you the new P38, hopefully that comes off ok!
 

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I have **exactly** the problem described in the OP's first post.

Ignition off, the temp gauge needle sits slightly below cold. Apply power via the ignition key and it will rise to the bottom of the blue part of the gauge.

Using Nanocom, once warmed up I see a constant 82-86 degrees C. Any fluctuation can be accounted for by thermostat opening/closing or ambient conditions.

I've checked as much wiring and as many connectors as possible but no joy.

I've read through the thread but don't have an oscilloscope, and may lack the knowledge to investigate further in that direction.

Was there a definitive solution found? (Fingers are firmly crossed here!)
 
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