1990s change display to metric

[Terry Griffin - CLC#20149]

My 1993 Sedan deVille fuel and aircon display is displaying Fahrenheit and Miles per Gallon.  I'd like to switch it to Metric.  I believe it can be done, but am unsure of how to do it.  I vaguely remember grounding pin M on the OBD1 connector would do it, but am very wary of messing with it in case it takes out the ECU.  Has anyone done this, and if so how please?  I do not have a digital dash.

[V63]

The best is to refer to the factory service manual or even owners manual

That said,  I believe it's done through the climate control panel, diagnostics initiated by pressing OFF and WARMER simultaneously.

[Terry Griffin - CLC#20149]

  Thanks to V63 for his input.

I've had a somewhat detailed read of the 1992/93 Deville/Fleetwood/Sixty Special service manual, and it would appear that on page 8D2-5 and several other circuit diagrams, the BCM can be switched from English (Imperial) to Metric simply by earthing BCM connector C2 (wire 811 Light Blue) for Metric and leaving it open circuit for English.  The 1993 Seville has such a switch on the top left of the digital cluster, but the analogue speedo cluster on mine does not have it.

Again, on page 8A-80-8 on the top right of the diagram, there is a section which specifies CANADIAN VEHICLES ONLY which shows the BCM connector C2 as permanently earthed.  Being an Aussie, I can only assume that Canada requires Metric displays rather the English/Imperial displays.  It does not appear possible to change the English/Metric parameter using the diagnostic system. Apart from output cycling, it can only be used for testing/diagnosis and displaying fault codes and clearing them.  It would appear there is no 'human' writeable memory in the BCM, unlike later versions with the OBD2 system.

The 1984 Sedan deVille I had some years ago used a similar OBD1 system and diagnostic entry method.

I'd be really pleased to see what others have discovered here.