speedometer died

[BobS]

at 360,000+ miles my speedometer and tach both died at once. (12 valve, 1996) Is this a PCM issue?

 

[GAmes]

Check the grounds. One of them is common to both gauges. Off the top of my head I don't recall which one.

 

[BigPapa]

Looks like two grounds for the cluster.

 

[BobS]

update, the temp gauge, voltmeter both work. Seems from the diagram they also share the ground with the dead tach and speedometer. Looks like I need to pull out the instrument cluster to check this wiring.

Since the tach is dead, the alternator does not put out any additional voltage 11.8 with the engine off, 11,8 with the engine running at various rpm. Is my reasoning correct?

 

[GAmes]

The PCM will not energize the alternator if it isn't receiving an RPM signal. Many times that is a case of a faulty ESS or a broken/chaffing ESS wire. However, a faulty ESS won't affect the speedometer. The PCM shares a ground with the ESS on top of the engine. You could look there too.

 

[BobS]

Resolution. After taking apart the dashboard, searching for any missing ground, I could not find the black/white ground wire under the dash, even though it is shown in the factory service manual. There is a black white ground attached to the top of the engine as GAmes mentioned and it was solid. After searching many previous posts on this, I disconnected the ESS at the connector and the speedometer came back to life. Geno's hooked me up with a ESS and all is working again. Kind of a pain to install without taking off the upper radiator hose. Thanks to all for their ideas.