84 300SD W126 outside temp LCD
 

I am trying to fix my outside temp LCD. I've read all the posts, but can't find an answer. So I thought my capacitor was bad. So I got it out and I have a 4 pin not the 5 pin. I only see two tantalum capacitors, can I replace those with aluminum ones? The backlight works and the screen is clear, no blackening or bleeding. The fuse is good. What else can I test?

It looks like you have 4 capacitors on that board, the yellow cylinder, 2 green blobs, and the blue can in the top right corner. The latter being the only one that should have issues (if you're replacing a capacitor, start there). Tantalum and ceramic capacitors rarely ever fail or drift in tolerance. They last for tens of thousands of hours.

What exactly is the unit doing? Lights on but nobody home? It's possible it's simply failed or the sensor doesn't have a good connection.

Thanks for the reply. I didn't even notice the blue one. No reading shows up "no ones home". I've checked all the connections, the sensor looks good, however I have not put a multimeter on it.

You need to check your sensor circuit with an ohmmeter. Check the resistance between pins 2 and 3 (brown and green). Post the resistance measured and approx. temperature.

Also check that you have 12 volts at the connector with a voltmeter with key on. Pin 1 +12 volt, pin 2 ground.

If you manage to get it running the default displayed value for open sensor is -36F. At -40 F and C are the same value, so the display will probably show something close to -40C.

Your bumper sensor should read as a rule of thumb when measuring it with an ohm meter
About 10k if it is cold (near 0 C or 32 F)
About 4k if it is pleasant (near 20 C or 68 F)
About 1.5k if it is hot (near 40C or 100 F)

Not true for all readouts. I've got one in front of me from a W126 and it goes blank when the sensor is removed. Mine however is not exactly the same as the OP's as it is a SWF instead of a VDO.

Thanks for the suggestions. I'll check the sensor tomorrow.

So I checked the resistance at the connector and got nothing. Checked the connector under the fuse box and got nothing. So pulled the sensor from the front and took a pic. Safe to assume it's no good?

Looks like you have found your problem.

When I checked the sensor the first time. I just stuck my head underneath around dusk. I thought it looked good.:eek:

But thanks to your other posts, I fixed my clock and odometer.

New sensor from peach parts and everything is working beautifully. Did the clock caps and new odometer gears.

any new fix for a black screen?

Yard had 3 Mercedes 300 cars listed and I packed tools. Checked site and they're gone. Too bad.