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SPEEDOMETER - TROUBLESHOOTING
August 2015. After taking out the instument panel, cleaning gauges and replacing the panel bulbs, for some reason the speedomter stopped working when everything was re-installed.
Perhaps it was static electricity or a loose connection, I'm not sure and apparently I'm not alone. Searching for how to troubleshoot the speedometer for a 1990 Suburban turned up
a whole lot of results but nothing concrete. To prepare, I had downloaded all the schematics and wiring diagrams I could find.
I happened to find a used 1990 Suburban (over 400,000km on it), it still had it's instrument cluster, so I purchaed it from the owner for $75 and for another $50 he threw in the
DRAC (Digital Ratio Adapter Controller) and the ECM (Electronic Control Module) just in case it was not the odometer itself.
The easiest and quickest thing to try was swap out the entire cluster with mine. Of course you have to remove the bezel and cluster, but there is only 1 connector (C203), and two bulbs with wires attached.
After swapping it, low and behold, the speedomter worked! So I knew the issue was isolated to the cluster. Still feeling like it was a fried odometer, I was prepared to just swap the working
odometer in my cluster.
To remove that connector, here is what I did. First, position the odometer like shown below, use the screw that secures both the odometer and fuel guage to act as a stop to
keep the odometer from moving to the right as you will be pullin on the connector in that direction. This will help hold the odometer from moving.
With a small flat head screwdriver, press the brass looking part inside the connector straigh down while pulling the connector off. It will take some force! I had rested the cluster
between my chest and a table lengthwise, screwdriver in one hand and the other hand pulling on the connector from the underside.
After getting the connector off, I had another look at the connector inside and it appeared when I repaired it and put the ribbon back in, it missed the mark and somehow wasn't
sitting in the right position to make contact. So instead of trying to repair something I already repaired and risk making things worse, I figured it was just easier to swap out
the entire printed circuit with the connector attached.
All the bulbs have to be removed as well as the metal retainers that hold the guages in (11 in total). Pinch them together with a pair of pliers from the top side and
they should drop out the back.
Once the printed circuit was removed, I had to remove some oxidization and corrosion on the conpper where the bulbs connected. I used a mixture of vinegar and salt, then after
cleaning the copper, I neutralized it with a mixture of baking soda and water.
I know this is not going to help a lot of you troubleshoot your odometer problems as you probably have a faulty odometer, DRAC / ECM or maybe a loose connection or broken wire,
but, hopefully this will help you get your odometer out in one piece. I do have a spare DRAC, ECM and cluster if you would like to purchase it from me. The ones on Ebay are going for $250+.