'94 Vandura: where is the speed/ABS sensor located?

[DmaxMaverick]

That ABS post applies to FRONT wheel sensors only. No relation to the rear, the speedo, or your problem.

Yes on the code reading. With a '94, you can use the ALDL (Assembly Line Diagnostic Link) to read the codes. You can find the process HERE, along with a list of the codes you might see.

Also, if you are in "limp mode", the tranny will stay in 2nd gear, if any forward gear is selected. It will not downshift to 1st, even if you select it. Unless you have 3.08 gears (doubtful) with tall tires, you can't get to 30 MPH in 1st, under power. This mode of limp mode will happen if the VSS signal is lost. The diagnostics for this circuit is not that difficult. Just ensure you have clean grounds and connections, then stay withing the circuit during your diagnostics. If you have no other symptoms, outside the intermittent loss of speedo and limp mode, the problem will be with the power or sensor return circuits (fuse, ign switch, connectors, sensor, VSSB). It could be a PCM issue, but only if all else has been eliminated. I suggest first cleaning connectors and grounds, and verify battery/alternator health. You can rule out speedo failure, as long as it isn't grounding the circuit, or feeding stray voltage back into the circuit (very rare).

[a5150nut]

When my transfer case was going south, it clogged the reluctor wheel with metal filings. Speedo problems and brake problems. You would be almost stopped then the brakes would go away. Lotsofun in stop and go traffic. Pull the sensor in the tail shaft to see if it is all fuzzy with metal filings. Just one more option that only costs time to check.

And welcome to TDP!