Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing GDI Gauges Intermittent Fault

Maybe this will help in fault finding your issue Mark. Only 8 of the 26 VDO master gauge connections are used and have identified each one by pin number, cable colour, purpose and source/destination as below:

Pin 1 - purple/red - keep alive +12 volts from engine fuse 3
Pin 2 - black - ground connection - to grounding eyelet shared with six others.
Pin 3 - slate/red - CAN high - shared data feed to instruments from pin 89 on ECU via engine loom
Pin 4 - blue/red - CAN low- shared data feed to instruments from pin 97 on ECU via engine loom
Pin 8 - pink - Kline - also normally used for OBD2 data - appears to only go to pin 7 on diagnostics socket
Pin 16 - pink/red - instrument illumination fed from instrument dimming potentiometer
Pin 18 - white/green - ignition switched +12 volt feed from engine fuse 10
Pin 19 - brown/white - frequency signal (0-40khz) fed from pin 86 on ECU via engine loom

I would also check engine fuse 10 (as well as aforementioned fuse 3) therefore and, by way of a shot in the dark, change both fuel pump and engine relays for Durite ones (well worth doing if you haven't already). Doubt if the issue is attributable to the sealed ECU but could of course be the Speedo. Otherwise hope this info helps.

Correction: Pin 19 - brown/white - speed signal from sensor shared to pin 86 on ECU via engine loom

Finally note the three data connections run through the engine loom to/from ECU so worth checking the integrity of the two connectors involved.

A quick note to thank you all.

Tony, that manual is for the GDI Gauges! So we know that the Gauges are from the VDO CANCockpit Series, which unfortunately are no longer available and no direct replacement, there does seem to be an upgrade path to the SingleViu range via a conversion Harness.

I ran the diagnostic routine which worked as described but didn't bring up any errors.

Richard, thanks for pulling this info together, more things for me to check.

Regards

Hi Mark

Another thing you could try. If the CAN BUS is a high speed bus, two of the modules connected to the bus will have a 120 ohm termination resistor connected between CAN high and CAN low, my guess would be the ECU and BCU. The CAN BUS will likely go to pins 6 and 14 of the diagnostics socket but confirm this. If that's the case make sure everything is switched off and the ignition key is out and then check for zero volts between pin 6 and 14 of the diag socket. Then set the meter to ohms and check the reading between these two pins, if it's a high speed bus it should be close to 60 ohms (two 120 ohms in parallel ). If so whilst monitoring the resistance reading waggle the splice joints CAN high and low one at a time also waggle the connectors to the immobiliser, BCU and ECU and speedo to see if any cause the resistance value to change. If one does you're onto a winner!!! For high speed data the terminations are important to prevent data errors.

The system has CRC data error detection. According to the VDO CANcockpit manual if data for a particular gauge is in error the data is discarded and the gauge pointer is driven to 6 degrees below zero so this is a possible cause of the symptoms you observe.

For a more detailed instruction on this test and other things you can do, watch the video link in Luddite's post from about 4:30 to about 7:00

Hope this is of some help

Regards Tony

Tony, this is the topology published by MMC for the Roadster showing hookup between ECU, BCU, instrument cluster and diagnostic socket.



It shows high and medium speed CANBUS and confirms your mention of two terminator resistors across CAN high and low and on each speed, these to prevent reflected signals at termination causing data corruption when bounced back. Since the GDI +4 uses similar BCU, albeit with the VDO master gauge system for instruments and no medium speed CANBUS used for same, it seems reasonable to assume it has otherwise a similar hookup.

Hi Richard

That's interesting thanks.

I can find no mention in the VDO CANcockpit manual about terminating resistors fitted across either of the two CAN bus's in the master gauge but it may be configurable. Easy to check though by removing the master gauge 26 pin connector whilst monitoring the resistance across the CAN bus pins at the diag socket to see if it increases to about 120 ohm.

Rog mentioned in his comment on this thread that the BCU pins can get mucky or corroded. My thought was that if on this vehicle the BCU is one of the units with a terminating resistor, bad pin connection might lead to a bus term missing or high value and hence as you say due to reflections data corruption to the instruments.

Regards Tony

Hi Tony, yes exactly

Here's one of my terminators (R30) next to the CAN chip on my MFU. Most likely the GDI's BCU will be similar. The connectors on mine are not what you would particularly class as, ruggedized.

Wow...Zach, Richard & Roger, I'm in awe of your knowledge on this stuff

We do need experts around the place...................