2001 Accord, V6, 4-door.
Tachometer is basically dead.
I know it receives it's electrical signal from the ECU.
FWIW, the Tach needle does move slightly when the vehicle is initially started so the problem cannot be a complete open circuit between ECU and gauge.
I'm electrical engineer and can test almost anything if I know what I'm looking at. However, after a lot of searching, I cannot find any information on the net, or in the shop manual, noting if the tach signal is based on frequency, voltage or current-loop. Short of substituting a known good gauge in the dash, does anybody know how to test the physical tachometer dash gauge or the ECU output signal? I'd hate to buy a replacement dash gauge only to find the root-problem is a bad ECU or something else.

Thx in advance for any possible assistance.

 

I have attached the wiring diagram for gauge panel. Signal is from PCM so must be digital, likely a 5V square wave input. An oscilloscope is necessary to discern the signal. You can backprobe w/ a T-pin at the gauge panel or at the PCM. Signal could be interrupted between PCM and gauge panel.

Usual fault is gauge panel. Check car-part.com and ebay for used options.

good luck

 

There is also the test tach connector in the engine compartment.

Signal: With engine running, pulses.

 

I have a Tektronix scope plus a high-end Fluke DVM that measures frequency.
Should be able to determine what is bad from info provided.
Thx

 

Solved by disconnecting battery for several minutes.
I forgot I have an OBDII device that will display running engine RPM.
When I plugged in, it correctly displayed engine RPM. That meant everything between the distributor and the ECM had to be working properly. Before I started digging into the electrical system further, I located another forum thread in which the poster noted that dropping ECM power (disconnecting battery) for several minutes basically re-booted the computer and THAT poster noted his tach began working again. Since it couldn't hurt, I tried it on my vehicle and it likewise fixed my problem.......tach now works properly. Essentially, I did a Ctrl-Alt-Del reboot on the ECM. I need to reset all my radio stations, but that's a small price to pay.

Thanks for the info provided. I'll certainly keep it around in case I need to dig further into the issue sometime in the future.