hondotexas

Hi, I have a 1999 4.0 4x4 and the gas gauge and speedometer quit at the same time (also low fuel lamp and trip), instrument panel self test ok, plugged into OBDII and have no signal from VSS, I can't see anything in common between gas gauge and VSS except sensor ground. Unplugged VSS and have 5.15 volts on pin 1, but when reading to ground (battery negative) on pin 2 for signal ground, circuit is open. What is normal for reading/how to test the signal ground on PCM? Haven't checked continuity from VSS connector to PCM connector yet (got dark). Is PCM signal ground supposed to be connected to chassis ground? Any ideas will be greatly appreciated.

Thanks

CCKen

The fuel gauge and the vehicle speed sensor share the same ground inside the PCM (PCM connector C1, pin A4). The ground circuit wires are spliced at splice S111. S111 is also the splice connnection for the downstream oxygen sensor. Splice S111 is located in the harness loom against the firewall, near where the fuel injector harness enters the loom. You may want to wiggle this loom/harness at this location and see if the Speedometer and Fuel Gauge come back to life. Note that there are several other sensors that grounds that splice in at S111.

The low fuel lamp is a function of the PCM. When it see a fuel quantity is around 1/8 tank it will put that light on through the CCD Data Bus.

Some sensors and relays that are grounded through the PCM, and/or have ground drivers in the PCM, are called hot grounds. If you went to pin 1 of the MAP sensor connector (Sensor ground at C1 A4) and usng a voltmeter, read from pin 1 to chassis ground with the key in off then run, you may read approximately .02 volts. Try it and see. If so, you should see .02 volts at pin 1 of the VSS connector. If not, these are not hot grounds [I haven't tried them]. I know the fuel pump relay pin 85 is a hot ground, so is the fan relay.

We'll go from here.